Pixel image standards. Image resolution and print quality. How to calculate dimensions for high resolution
Many of us love to take photographs. The variety and availability of digital cameras make photography a popular pleasure, allowing us to capture the bright, colorful moments of our lives. Wherein high quality the resulting photographs does not guarantee the same quality when printing digital photographs on standard roll photo paper. In this material, I will tell you what sizes of photographs there are for printing, provide tables of available formats, and also give a number of examples that will allow you to clearly understand the features of different photo sizes.
To understand what sizes of photographs there are for printing and what their specifics are, we need, first of all, to understand the basic concepts necessary to understand the digital printing process.
Linear photo size– photo dimensions in millimeters (width-height).
Photo parameters in pixels– the dimensions of your photo, expressed in the number of pixels (width-height).
Pixel– the smallest element of the image, usually a rectangular or circular point, and a certain color. An image consists of hundreds and thousands of such pixels, which are counted both horizontally (width) and vertically (height). For example, an image size of 1181x1772 (usually the standard photo size of 10x15) is 1181 pixels wide by 1772 pixels high.
Moreover, the more such pixels in your image, the higher quality it usually is, with better detail and rendering of objects.
Aspect proportions– aspect ratio of the photograph (for example, 1:1, 2:3, 3:4, and so on). The parameter shows how much shorter or longer one side is than the other.
Raster image (raster)– an image consisting of such pixels.
DPI– (an abbreviation for “dots per inch” - dots per inch) is a parameter used to characterize the resolution of photo printing, that is, the number of dots per inch (an inch is 2.54 cm). The basic printing standard is 150 dpi, the optimal is 300 dpi. Accordingly, the higher the DPI, the higher the print quality of the existing digital photo.
Standard (format) photo- this is a template aspect ratio of a photograph, which is important to adhere to in order to obtain the final image on paper.
Why is it important to consider standard photo sizes?
In the vast majority of cases, the digital photographs you receive will be printed on photo paper of standard sizes. If the proportions of digital photographs and the selected photo paper sizes do not match, the photographs may come out stretched, not clear, lose image quality, and have other undesirable consequences for you.
Therefore, it is important to compare the standard photo sizes for printing and the pixel sizes of the digital photos you have to choose the optimal printing format.
Popular photo sizes for printing with format table
The generally accepted standard photo is 10 by 15 cm in size. However, the size of a commensurate digital photo is usually slightly larger (for example, 10.2 by 15.2 cm), and the size in pixels of this photo will be 1205 by 1795 pixels.
Other formats are shown in the table below:
If you plan to work with large-format printing, then it has quite broad requirements for digital images:
If you know the dpi parameter and the number of pixels of your photo, then using the formula below, you can calculate required dimensions sides of your photo:
In this formula:
x is the required size of one side of the photograph in centimeters;
r – photo side resolution in pixels;
d - 2.54 cm (standard inch);
dpi – usually 300 (less often – 150).
For example, let the image width be 1772 pixels and dpi=300.
Then 1772*2.54/300=15.00 cm in print width.
Popular photo formats
In addition to the classic size 10 by 15 (A6 format) that I have already mentioned, there are other popular photo sizes for printing. Among them I would highlight the following:
Conclusion
This article provided standard photo sizes for printing, popular photo formats, as well as a convenient formula for calculating the optimal size of the sides of a photo. I recommend sticking to the formats I have given, this guarantees the quality of the printed photographs, and therefore the visual pleasure of viewing them.
Size, resolution and formats... What happens to the pixels? Are you buying a camera based on the megapixel count? Do you have problems posting photos online? Are your photos printed in poor quality even though they look great on screen? There seems to be some confusion between pixels and bytes (image size and file size), quality and quantity, size and resolution. In this lesson we will look at this extremely important information for any photographer.
So let's look at some basic concepts to make your life easier, your workflow more efficient, and your images will have right size for intended use.
This image is 750 × 500 pixels with a resolution of 72 dpi, saved in compressed JPG format, which is 174kb. Let's figure out what this all means.
Are resolution and size the same thing?
One of the biggest misunderstandings comes from the concept of resolution. If this is your case, trust me that you are not alone.
The problem is that permission can refer to many things, two of which can be problematic. I'll explain these two concepts of resolution next, but they have one thing in common that I need to clarify first. They both have to do with pixels.
You've probably heard a lot about pixels, at least when you bought your camera. This is one of the clearest and most "essential" specs on the market, so I'll start there.
What is a pixel?
Digital photography is not one inseparable thing. If you zoom in far enough, you'll see that the image looks like a mosaic made up of small tiles, called pixels in photography.
The number of these pixels and the way they are distributed are two factors that need to be considered to understand what resolution is.
Number of pixels
The first type of resolution refers to the number of pixels that form your photo. To calculate this resolution, you simply use the same formula you would use for the area of any rectangle; multiply the length by the height. For example, if you have a photo with 4500 pixels on the horizontal side and 3000 on the vertical side, it gives you 13,500,000. Since this number is very impractical, you can simply divide it by a million to convert it to megapixels. So 13,500,000/1,000,000 = 13.5 megapixels.
Pixel Density
Another resolution is how you distribute the total number of pixels available, which is commonly called pixel density.
Resolution is now expressed in dpi (or ppi), which is an abbreviation for dots (or pixels) per inch, and yes, per inch, it just so happens that in metric system it wasn't translated. So, if you see 72 dpi, that means the image will have a density of 72 pixels per inch; if you see 300 dpi, that's 300 pixels per inch, etc.
The final size of your image depends on the resolution you choose. If an image is 4500 x 3000 pixels, that means it will print at 15 x 10 inches if you set the resolution to 300 dpi, but at 72 dpi it will be 62.5 x 41.6 inches. Although the print size changes, you are not changing the size of your photo (the image file), you are simply changing the organization of the existing pixels.
Imagine a rubber band, you can stretch it or compress it, but you don't change the amount of tape, you don't add or cut it.
So resolution and size are not the same thing, but they are related.
So does quantity mean quality?
Because of the aforementioned relationship between size and resolution, many people think that megapixels mean quality. And in a sense, this is because the more pixels you have, the higher their density.
However, aside from the quantity, you also have to consider the pixel depth, this is what determines the amount of tonal values your image contains. In other words, it is the number of colors per pixel. For example, a 2-bit depth can only store black, white, and two shades of gray, but a more common value is 8 bits. The values grow exponentially, for example with an 8-bit photo (2 to 8 = 256), you would have 256 shades of green, 256 shades of blue and 256 shades of red, which means about 16 million colors.
This is already more than the eye can distinguish, which means that 16-bit or 32-bit will look relatively the same to us. Of course, this means that your image will be heavier even if the size is the same, because each pixel contains more information. This is why quality and quantity are not necessarily identical.
So quantity matters, but the size and depth of each pixel also determines quality. That's why you should look at all the specs of the camera and its sensor, not just the megapixel count. After all, there is a limit to the size you can print or view, what's more, it will only result in additional file size (megabytes) and will not affect the image size (megapixels) or quality.
How to select and control image size and file size?
First of all, you need to decide what maximum density you need. If you post your image online, you can do just fine with just 72 dpi, but that's too low to print the photo. If you're going to print, you'll want between 300 and 350 dpi.
Of course, we're speaking in general because every monitor and every printer will have slightly different resolutions. For example, if you want to print a photo to 8×10 inches, you'll need the image to be 300 dpi x 8" = 2400 pixels and 300 dpi x 10" = 3000 pixels (so 2400 x 3000 for an 8×10 print at 300 dpi). Anything larger will only take up space on your hard drive.
How to resize inPhotoshop
Open the Image Size menu and in the pop-up window you need to check the “resample” box. If you don't enable "resample" you will be redistributing pixels as I explained at the beginning of the article.
You can also select the Proportion checkbox if you want the settings to be adjusted according to your changes. So the width changes when the height changes and vice versa.
8x10 inches at 300ppi, this is the size needed for an 8×10 print. Note the 3000 pixel sizex 2400.
750x500 pixels at 72ppi. This is web permission and this is Exact size all images in this article. Inch size doesn't matter when publishing online - only pixel size matters.
At the top of the window you will also see the file size changing. This is the uncompressed version of your image, which is the direct connection I talked about in the first part of the article: fewer pixels means less information.
Now, if you still want to resize the file without resizing, then you can do so when you save the image. Before saving the photo, you can select the desired format:
If you don't want to lose any information, you need to keep the uncompressed format. The most common is TIFF.
If you don't mind losing a little information and having a lighter file, go to JPEG and choose how small you want it to be. Obviously, the lower the value you set, the more information you will lose. Luckily, it has a preview button so you can see the impact of your compression.
JPG high quality.
JPG low quality. Notice how it's pixelated and broken up? If you choose a very low quality, you risk degrading the image too much.
Conclusion
So that's what quality, quantity, size and resolution mean, and they all relate to pixels as they are the basic units that make up an image. Now that you know how to make the best choices for printing, sharing, and storing your photos. All this information is laid out in more detail in the video course: “Secrets of creative photo processing for a beginner”; to read the course description, click on the picture below.
To watch the video, click on the picture.
You will learn:
- What is image resolution and what file formats are there?
- How to change the size and resolution in the Image Size window.
- What are the types of interpolation algorithms?
- How to prepare an image for posting on the Internet using
- Save for Web window.
- How to get the minimum file weight when saving as JPG and GIF.
- How to save as PNG, PNG-24, TIFF, PDF and PSD.
The lesson consists of the following sections:
1. Training video.
2. How does Resolution affect the quality of the image.4. Increase in size without loss of quality.
5. Plugins for resizing images.
6. Prepare the image for posting on the Internet.
7. Save for Web.
8. Saving in JPG format.
9. Save to GIF format.
10. Save in PNG format.12. Saving in PDF format.
13. Save to PSD format.
14. Questions.
15. Homework.
How does Resolution affect image quality?
We have already mastered the basics of the program, made our own works and now we want to show them to others. This section will talk about how to do it correctly. The quality of a photograph depends on many factors. One of the most important is resolution.
Resolution is the number of pixels that make up a raster image. Many of you have encountered a situation where the resolution of the camera was deliberately reduced (more photos will fit on the memory card, but they look good on a small display). Remember the first cameras in mobile phones with a resolution of 0.3 MP. And then, transferring the photographs
into a computer onto a large monitor, we were disappointed with the quality, which was irretrievably lost at the time of shooting. When you enlarge those photos in a graphics editor, the result becomes even worse. Slanted lines become jagged and the photo appears blurry. Pixels determine how sharp an image appears to us, and their number is responsible for the maximum print size without loss of quality.
At the bottom left edge of the program window is the Status Bar.
Here you can change the display scale. Next to the scale column is information about the document. By clicking on the arrow, you will be taken to an additional menu. Select the commands that you consider necessary to provide information.
This field is convenient, but does not allow us to resize it to suit our needs.
To change the resolution or size, select from the menu Image(Image) -ImageSize(Image size). Or clickAlt + Ctrl + I.
From the Width and Height drop-down menus located in the Document Size group, select the units of measurement. Percentage, inches, cm, mm, points, pcs, columns.
dpi – dots per inch (dots per inch) – Units for measuring print resolution.
ppi – pixels per inch (pixels per inch) – Units of resolution for computer monitors.
Resolution(Resolution) – the number of pixels in 1 inch or centimeter. Which resolution should I choose?
72 ppi is quite enough to display photos on a monitor screen. This is also sufficient for Web graphics. When you zoom in on such images, you will not be able to see small details, because they are not there.
300 ppi – it is advisable to set it for photographs that you want to put up for sale or print on a printer. Although for printing the average value is 267 ppi. In high-resolution images, when you zoom in, you can see fine details.
For units of measurement, select pixels / inch (pixels per inch), rather than pixels /cm. We, who are not used to measuring in inches, need to be especially careful not to choose pixels / cm just because we like centimeters better. The difference of 2.54 times will immediately affect your resolution. The files will become gigantic. So when working in this window and when creating a new document, make sure that pixels per inch are selected.
ScaleStyles(Scale styles)– allows you to scale the styles specified in the Layers palette along with the selected layer.
ConstrainProportions(Keep proportions)– link height and width, so that when one parameter changes, the other also changes. The most common mistake made by beginners is the absence of this checkbox. As a result, the image is flattened or stretched.
Resample Image (Interpolation/Track changes). If you check this box, changing the image resolution (pixels per inch) will resize the image while maintaining the original resolution. If you uncheck the box, increasing the image resolution (for example, from 72 to 300) will lead to a decrease in the geometric dimensions of the image when printed. Be careful not to end up with a postage stamp sized print.
Interpolation algorithms can be selected in the drop-down list. Depending on this choice, the result is different. It's worth spending a little time to test them in action.
When reducing the resolution, problems usually do not arise, since the graphic information is simply discarded. But to enlarge the image, the program has to generate new pixels based on an analysis of their neighbors. When adding new pixels, the program does not always produce a result that would satisfy us.
Resampling is always accompanied by losses in quality. Except for interpolation with a reduction in the number of pixels to eliminate scanning defects and increased image grain. When scanning, select a resolution that is significantly higher than necessary. Resample with reduction in several stages. Grain and other artifacts will be eliminated.
Nearest Neighbor (By neighboring pixels). Maintains crisp edges. The simplest algorithm
as a result of which the edges have characteristic jagged edges.
Bilinear. The average value is calculated based on the analysis of neighboring pixels horizontally and vertically.
Bicubic. Best for smooth gradients. The average value is calculated based on the analysis of neighboring pixels not only horizontally and vertically, but also diagonally. This interpolation method works with big amount adjacent pixels, makes serious calculations of the values of these elements and creates new pixels that should be in this place. For small photo enlargements, this method is quite suitable.
From CS onwards, two new interpolation algorithms have appeared. I recommend using these:
Bicubic Smoother Best for enlargement.
Bicubic Sharper (Bicubic sharper). Best for reduction. If you resize images most often, set this algorithm as your default. To do this, select it in Edit – Preferences – General. The changes will take effect after you restart Photoshop.
Increase in size without loss of quality
I found on the Internet a simple way to increase the size of an image with a slight loss of quality and decided to check if this was true. I took a small picture measuring 5 by 5 cm and enlarged it 2 times using Bicubic Smoother interpolation. To the right of the Width and Height fields, select %. Enter 110 in these fields to increase the image size by 10%.
Increasing the image size by 10% does not reduce its quality! To enlarge a small image many times, you need to increase its size by 10% several times (I had to run this command 8 times).
Then I decided to record an Action to gradually enlarge the image, in the hope that the quality would be better and I could use this formula at the next enlargements.
By the way, this is very easy to do: open the Action palette (Operations/Scripts). It is located next to the History palette. Click on the create a new operation button. A window will appear in which you need to enter the name of the operation (for example, increase by 2 times 10). The circle at the bottom of the palette will turn red, which means recording has started. Change the Image Size as mentioned below 8 times and click on the leftmost "Stop" box. All! Now, to perform this operation, just mark it with the cursor and press the Play button. You will find detailed information about Action (Operations) in the automation lesson.
The results of the experiment are presented below. Do you see the difference? Me not. But maybe my eyesight is failing me. It seems to me that both results have become noticeably worse compared to the small source.
So is the game worth the trouble if the difference is barely perceptible? And did people really come up with this algorithm in vain? No, not in vain. There really is a difference, but it is noticeable only at very high magnification (300% and above). The blurriness of the image after Resample Image will be visible only when printing the image, on the screen it
When using the transformation tools (Ctrl+T), the image size also changes. Moreover, this happens so quickly that we don’t even have time to think about how much the quality will suffer. Interpolation algorithms mercilessly eat pixels when decreasing and add new ones when increasing.
Plugins for resizing images.
Photoshop has plenty of options for resizing an image. However, other manufacturers cannot be ignored.
- Alien Skin – BlowUp v1.0 plug-in for Adobe Photoshop. Better than bicubic interpolation. The plugin maintains smooth, crisp edges and lines when resizing the image, and creates four times (1600%) magnification without the appearance of aliasing artifacts or glows. In some cases, Blow Up allows you to enlarge an image up to six times without visible artifacts.
- SizeFixer SLR – Allows you to enlarge images up to A1 format
- SizeFixer XL. – Unlimited increase.
- PXL SMARTSCALE – Enlarges up to 1600% without losing print quality.
If you set yourself a task, you can find others worthy representatives. I won't recommend anything. Personally, I find it convenient to use one program, Photoshop. But time goes by quickly, perhaps when you read this text a new super plugin or software will appear that I don’t know about yet. Well, we will continue to change sizes and resolutions using Photoshop.
We will prepare an image for posting on the Internet.
The usual Save (Save) Ctrl+S and Save as... (Save as...) Shift+Ctrl+S do not allow you to control the result, and the file weight is large.
Despite the fact that in the save window there is a slider that regulates the compression quality, the file size obtained at maximum quality is still larger than when choosing another command Save for Web.
Select from menu File(File) – SaveforWeb(Save forWeb). Key combination Alt + Shift + Ctrl + S. In this window we can observe how the quality changes when the image is compressed. You can also control the weight of the file and its download speed. It is most convenient to work with tab 2 - Up (2 options), because you can compare how much the quality will suffer for the sake of low weight (it is important that the images on the site load quickly). Below the image there are comments: compression format, file size after optimization and loading time.
The right side of the window contains all the main optimization settings.
There are five saving formats for the Web: GIF, JPG, PNG-8, PNG-24 and WBMP. The latter is practically not used.
IN JPG It is best to store large files of website backgrounds and photographs for publications in GIF, PNG-8 and PNG-24 - design elements that have a small volume and a limited number of colors. Unfortunately, PNG-24 is not supported by Internet Explorer 6, but the number of IE6 users is rapidly decreasing and, therefore, the risk that the PNG-24 format will not open on someone's computer is decreasing.
GIF and PNG-8 files retain transparency (but not the alpha channel). To maintain transparency, you need to check the Transparency checkbox. WBMP is a raster format for mobile phones.
Once you click "Save" and enter a file name, this window will appear. It is only needed to remind you that it is better to write the file name when saving in English letters, without spaces or capital letters. If you don’t want to see it in the future, check the box “ Don't show it again."
Saving in JPG format.
JPG – the most common format for storing photos. The advantage is the relatively small file size. The main disadvantage is lossy compression. Small details are lost, stains and moire appear. Repeated rewriting causes gradual distortion of details, leading to a significant loss of quality.
The settings for the JPG format consist mainly of adjusting the image quality (aka compression) in percentage. To save big piece background blur can be increased.
To control the image size, Save for Web has a section called Image Size. The dimensions of your image should not exceed 800 by 600 pixels. Or an impatient user will close the browser window without waiting for the image to load completely.
Open the file boat.jpg. Select Save for Web from the File menu. Select 2-Up mode. In the Image Size section, reduce the image size to 450*600. You can do this first by selecting Image – Image Size from the menu, or by pressing Alt + Ctrl + I.
In the list on the right side of the window, select the JPEG saving format.
List Compression quality offers several values - from Low (Low) to Maximum (Best). More precise adjustment is made using the Quality slider located to the right. To start, set it to 100%. At such a high value the image
on the right side of the viewing area (optimized) is practically no different from the original
on the left side. Take a look at the information fields in the corresponding parts of the viewport. The original (uncompressed image) takes up 625 KB, and the compressed image takes up 139.5 KB. Even with such a low compression ratio there is a significant benefit in file size. The loading time for a compressed image is 26 seconds - this is too much, many may lose patience and leave
from your page.
Set the Quality slider in the middle, about 50%. Do you see the difference between the two images? No? Then you can reduce the Quality a little more. Let's stop at 35%. Below 30 there will already be a noticeable deterioration. The weight became 23 kb, and the speed was 5 seconds. Sometimes the Blur option can save you an extra second or two. But in our case, it will not give a noticeable result, because We have already compressed the image quite strongly.
Progressive sets the progressive scan of the image when loading in the browser. This option allows you to load the image gradually. From the very beginning of the download, you will see part of the image.
Optimized includes additional optimizations to the internal structure of JPEGs, sometimes reducing file size even further.
ICC Profile (Built-in Profile/ICC Profile) allows you to embed a color profile into an image file. The embedded profile increases the file size. Check this box only if you think it is necessary for others to know what your color profile is.
Click on the preview button and you will see how your image will open in the browser. You can choose to view any of the browsers installed on your computer.
Save your settings if you need to process many images. To do this, click on the optimization menu icon and select Save Settings. Enter a name in the File name field and click the Save button.
The name you entered will now appear in the Settings list. When processing the next file, it will be enough to select this name from the list.
Saving as GIF
To place images with transparent areas on a Web page, the format is used GIF, which only supports indexed colors.
The number of colors in its palette is specified in the field Colors and should create a relationship between quality and weight.
In the list of algorithms for generating an indexed image palette, the default option is Selective, which gives the best results for images.
The following dropdown list is the default option Diffusion (Diffusion/Random) best used for photographs, a Noise– for background textures and gradients. Pattern creates a repeating pattern.
Interlaced– for gradual loading of the image.
The degree of smoothing is set with the slider Dither (Dithering/Smoothing). The higher the smoothing, the larger size file.
List Matte (Matte/Border) Creates a transition between the edge of an image and the background color of the page. Typically the edge is semi-transparent, which is not supported by the GIF format.
As a result, characteristic noise occurs during export. To avoid its appearance, set the background color of the Web page in the list. Translucent pixels will be colored this color. If you uncheck Transparency, the color specified in the Matte list will be considered the background and fill the transparent areas of the image.
Colors are transferred to the Web palette using a slider Web Snap (Web colors). Observe how the colors of the image change depending on the position of the slider. Changes that occur are displayed in the image palette. White diamonds appear on some colors of the palette.
Color Table useful for more than just observation. It allows you to control individual colors in an image.
Clicking on the icon will open an additional list.
If you want to avoid significant color shifts in all browsers, but do not want to bring all colors to the Web palette, you can do this selectively. Set the sort mode to Sort by Popularity. The most frequently occurring colors will be arranged from left to right.
Click on any swatch in the palette. The swatch will have a white border indicating that it is selected. Photoshop can choose the color closest to the selection from the Web palette. To do this, click on the cube icon at the bottom of the panel or select the command Shift/Unshift Selected Colors to/from Web Palette.
Converting the entire image to the Web palette made the transitions on the monitor image too sharp. We will fix this defect manually. Double-click on the sample in the palette. The Color Picker window will appear in front of you. Make sure that the Only Web Colors checkbox is checked. Select the shade closest to the current color and close the window by clicking OK (Yes). The color will be edited. If you find it unsuccessful too, open the Color Picker window again and select another one.
A white square in the bottom corner of the swatch indicates that the color is locked. Blocked colors remain intact when reducing colors in the image palette and when viewed in the browser. To unlock the lock, click on the padlock icon
at the bottom of the panel.
Save in PNG format.
PNG allows you to store both indexed and full-color images. The compression algorithm used does not lead to information loss. Repeated processing and rewriting is free of the disadvantages inherent in the JPG format. The formats are PNG-8 for indexed images and PNG-24 for full color. The parameters of PNG-8 are absolutely similar to GIF, in PNG-24 there is only switching between Transparency and Interlaced modes.
and Matting parameters.
To save, use the File Menu – Save as…. In the File type field, select TIFF.
TIFF supports lossless compression at the cost of a larger file size than JPG. This format is considered the best for saving scan results, sending faxes, text recognition and in printing for printing. It is possible to save an image with different compression algorithms and without compression at all.
TIFF preserves transparency and alpha channels. In PhotoShop, you can save a file containing layers.
TIFF stores ICC profile information. This makes it possible to preserve colors without changing when viewed on different monitors and when printed.
TIFF is widely used on both the IBM PC and Apple. This allows it to be used to transfer images from one hardware platform to another without losing content. This format can also be used to transfer data between different applications that do not “understand” each other’s formats, but “know” TIFF. With such a transfer, many image attributes will be preserved, which are lost, for example, when transferring data through the Windows clipboard.
Saving to PDF format
PDF is a presentation format electronic documents(paperless office). The main advantage is that documents look the same on any device (screens, printers). Design elements do not move in different directions.
To save, use the File Menu – Save as…. In the File type field, select PDF.
In the Security System section, you can set a password for opening a file, printing, saving, and editing.
Save to PSD format
PSD is PHOTOSHOP's own format. In it you can save layers, masks, clipping masks, paths, text and other aspects of unfinished work.
Questions:
- Which file format does not support lossless compression?
- Which interpolation algorithm is best for increasing image resolution?
– Nearest Neighbor (By neighboring pixels)
– Bilinear
– Bicubic (Bicubic)
– Bicubic Smoother
– Bicubic Sharper (Bicubic sharper)
- What resolution should I set to save images for the Internet?
- What needs to be done in the Image Size window so that the image can be resized while maintaining the original resolution?
– Check the Scale Styles checkbox.
– Check the Constrain Proportions checkbox.
– Check the Resample Image checkbox.
– Uncheck Resample Image.
– Uncheck Scale Styles.
- Is it possible to resize an image in the Save for Web window?
- What file format cannot be selected in the Save for Web window?
Homework:
1. Open the photo boat.jpg. Save to JPG format using Save for Web. Achieve the following indicators: image size 600*800 pixels; 39.49 k;
8sec /56.6 kbps.
2. Open the photo boat.jpg. Save to GIF format using Save for Web. I was able to compress it to 75 kb and achieve a download speed of 14 seconds at 56 kbps. Try to achieve better results.
You'll have to change the colors.
02/24/15 46.2KIn this article, we'll look at how image resolution affects print quality.
Have you ever downloaded a picture from the Internet and then when you printed it, got results that were, well, smaller than you expected? The image looked great on your computer screen, but when you printed it, it either printed at size postage stamp or normal size, but looked blurry or “blocky”? The reason is the image resolution.
In fact, this is not entirely fair. It's not that the image resolution is specifically set in such a way as to make you unhappy when you print a photo from the Internet. The problem is that most photos on the Internet are very small pixel sizes, typically around 640 pixels wide by 480 pixels high. Or even less.
Because the image doesn't have to be very large to look good on a computer screen. And also because small images load much faster than larger ones ( this is a completely different question that we will not touch on in this article).
So what can we do to make photos downloaded from the Internet look like this when printed? high quality photos from a digital camera? The answer is absolutely nothing. In most cases, online photos simply don't have enough pixels to print at high quality. At least if you don't print them in postage stamp format. Let's find out why.
First of all, let's move a little away from the topic of downloading images from the Internet, as such, and the fact that we really shouldn't do it anyway without the permission of the copyright owner. Let's look at image resolution in general.
The term " image resolution" means how many pixels of your photo will fit on each inch of paper when printed.
Obviously, since your photo has a fixed number of pixels, the more pixels there are in one inch, the smaller the image will appear on paper. Likewise, the fewer pixels per inch you print, the larger the image.
The number of pixels per inch when printing is called " image resolution". Image resolution determines the print quality of the image. It has nothing to do with how the image is displayed on a computer screen. That's why photos downloaded from the Internet tend to be much higher quality on screen than when you print them.
Let's take a photo as an example:
Not a very good photo of a horse
I can't help but laugh every time I see this photo of a horse that I took while driving through rural areas. Normally this horse is a proud, powerful, dignified animal, but I seem to have caught him in a rather unsightly position. She's standing at a slightly odd angle, straw hanging from her mane, and I think I caught her chewing her food.
Either that or she's desperately trying to smile at me. In any case, this horse is already embarrassed that I caught him at such a moment. Let's use this image as an example.
First, let's see what Photoshop can tell us about the current size of this photo. I go to the "Image" menu at the top of the screen and select " Image Size", after which a dialog box appears with the corresponding name " Image Size«:
The Image Size dialog box shows us the current photo size
Dialog window " Image Size"is divided into two main parts: " Dimensions in pixels"at the top and " Document Size"directly below it.
« Dimensions in pixels" indicate how many pixels our image contains. " Document Size” tells us how large the image will appear on paper if we print it. If we look at the section " Dimensions in pixels", then we see that this photo has a width of 1200 pixels and a height of 800 pixels. This may seem like a huge number of pixels ( 1200 by 800 = 960000 pixels!).
And this, of course, would be the case if we were displaying an image on a computer screen. In fact, at 1200 by 800, it may be too large an image to fit entirely on your monitor!
But just because it looks nice and big on screen doesn't mean it will be nice and big on print. At least not with a high degree of quality. Let's take a closer look at what the section " Document Size»:
The Document Size section tells you how large or small the photo will be when printed at a certain resolution.
Chapter " Document Size» dialog box « Image Size" allows us to know two things: what the current resolution of our image is and how big or small the image will be if we print it based on that resolution.
We currently have our resolution set to 72 pixels/inch, which means that out of the 1200 pixels that make up the right to left edge of the photo (the width), there will be 72 pixels for every inch of paper. And of the 800 pixels that make up the image size from top to bottom (height), there will also be 72 pixels for every inch of paper.
The value in the Resolution field is determined for the width and height, not the total number of pixels. In other words, for every square inch of paper, there will be 72 pixels per inch of height and width. Total pixels printed in each square inch of paper, which would then be 72 by 72 ( 72 pixels in width and 72 pixels in height). Which gives us 5184 pixels!
Let's do some simple math to make sure that the width and height shown to us in the " Document Size"is correct. We know from the section " Size in pixels"that we have 1200 pixels from left to right and 800 pixels from top to bottom. Print resolution is currently set to 72 pixels/inch.
To figure out how big our image will be when printed, we just need to divide the number of pixels from left to right by 72, which will give us our image width when printed. And also divide the number of pixels from top to bottom by 72, which will give us the height when printing. Let's do that:
1200 pixels wide divided by 72 pixels per inch = 16.667 inches wide
800 pixels divided by 72 pixels per inch = 11.111 inches in height
Based on our own simple calculations, at a resolution of 72 pixels/inch (ppi for short), our image would be 16.667 inches wide by 11.111 inches tall when printed. And if we look at the section " Document Size" again:
Confirm print sizes in the Document Size section
This is exactly what is stated here! Wow, a 1200 by 800 pixel photo is large enough to print at 11 by 14 inches, we can even make it smaller a bit! Amazing!
Unfortunately no. If only everything in life were so simple.
The fact is that 72 pixels per inch is not enough to give us a sharp, good quality, professional-looking image in print. Not even close. To give you an idea of what I mean, here's a rough approximation of what the photo would look like on paper if we tried to print it at 72 pixels per inch.
You'll have to use your imagination a little. Try to imagine it's 11 by 16 inches:
What will a photo look like on paper when printed at a resolution of only 72 pixels per inch?
Doesn't look too good, does it? The problem is that 72 pixels per inch provides too little information about the image to print a sharp, clear photo on paper. It's like not enough peanut butter has been spread on a large piece of toast. The photo now looks blurry, boring and generally unattractive.
We don't see this on a computer screen because computer monitors are generally referred to as low-resolution devices. Even a photo with relatively small pixel dimensions, such as 640 by 480, will look great on a computer screen.
Printers, however, are devices high resolution, and if you want your photos to print clearly and show all the fine detail, you need a resolution much higher than 72 pixels per inch.
So what is the maximum resolution value needed for printing? professional quality? It is generally accepted that this is 300 pixels per inch. Printing an image at 300 pixels per inch compresses the pixels enough to maintain sharpness.
In fact, 300 is usually a little more than you need. You can often see photos at 240 dpi resolution without any noticeable loss in image quality. However, the professional standard is 300 pixels per inch.
Let's take the same image, with the same 1200 pixels width and 800 pixels height, and then change the resolution from 72 pixels per inch to 300 pixels per inch, and see what happens.
Here is the dialog box " Image Size» with a new resolution of 300 pixels per inch. Please note that in the section " Size in pixels"at the top we still have 1200 pixels in width and 800 pixels in height.
The only thing that has changed is our resolution - from 72 to 300:
Print resolution has been changed to 300 pixels per inch
The fact that the resolution has increased from 72 to 300 pixels per inch means that of the 1200 pixels that our image is wide, 300 pixels are printed on one inch of paper. And out of 800 pixels of height, 300 are printed for every inch of height of paper. Naturally, with so many pixels per inch of paper, the printed photo will be much smaller.
And of course, the Document Size section now says that our photo will print at just 4 inches wide by 2.667 inches tall:
The photo will now be printed in a much smaller size than before
Where did these new width and height values come from? Again, some simple math:
1200 pixels wide divided by 300 pixels per inch = 4 inches
800 pixels high divided by 300 pixels per inch = 2.667 inches
The photo will now be printed at a much smaller size than it was at 72 dpi. But what we lose in physical size we more than make up for in image quality. At 300 pixels per inch ( or even at 240 pixels per inch) we will enjoy clear, professional quality results:
Higher print resolution results in smaller photo sizes, but the image quality is much higher.
Of course, most people don't print their photos in custom formats like 4 by 2,667. So how do we make sure we get professional quality results when printing in a more standard format like 4 by 6? Great question, and we can get the answer by turning to boring arithmetic again.
Let's say you took photos from your recent family vacation, taken with a digital camera, and you want to print some of them on a 4 by 6 printer. Now we know that in order to achieve professional quality photos, we must set the resolution images at a minimum of 240 pixels per inch. Although the official standard is 300 pixels per inch.
Let's look at both of these resolutions to see how large camera images need to be in order to print them in good quality in a 4 by 6 format. First, let's look at 240 pixels per inch.
To figure out how large in pixels our images need to be for them to print at 4 by 6 in professional quality, we just need to multiply 240 by 4 for the width, and then 240 by 6 for the height ( or vice versa, depending on whether your photos are in landscape or portrait orientation).
Let's do that:
240 pixels per inch x 4 inches wide = 960 pixels
240 pixels per inch x 6 inches high = 1440 pixels
Based on these calculations, we see that in order to print a digital photo in 4 by 6 format at 240 pixels per inch, and still maintain excellent quality, the photo's pixel size must be at least 960 by 1440. We see also how many pixels should a photo have overall, 960 times 1440 gives us 1382400 pixels.
Let's round this value to 1,400,000 pixels. It may seem too much a large number, but in fact it is. 1.4 million is the minimum number of pixels needed to print a 4 by 6 photo at the minimum normal quality resolution of 240 pixels per inch.
The good news is that most digital cameras on the market today are 5 MP (“ mega pixels" or "millions of pixels") and higher. So you won't have any problem getting good quality 4 x 6 prints even at 300 ppi.
Of course, we haven't yet calculated exactly how many pixels we need to have to print a professional-quality 4 by 6 photo at 300 pixels per inch. So let's do it. We will use the same simple formula that was described above.
We'll multiply 300 by 4 and then 300 by 6 to get the pixel dimensions we'll need:
300 pixels per inch x 4 inches wide = 1200 pixels
300 pixels per inch x 6 inches high = 1800 pixels
Let's do another quick calculation to see how many pixels we need in total:
1200 pixels wide multiplied by 1800 pixels high = 2160000
So, in order to print photos in 4 by 6 format in good quality using professional standard At 300 pixels per inch for resolution, our photo should be 1200 pixels wide by 1800 pixels high (or vice versa). This means that we should have a total of 2,160,000 pixels. Which again shouldn't be a problem for most digital cameras on the market that are 5MP or larger.
But what if you have a photo you adore and think it deserves to be printed in 8 by 10 rather than 4 by 6? How big does an image need to be so that it looks good when printed at 8 x 10? The answer to this question is as easy to give as before.
All you need to do is multiply the resolution value in pixels per inch by the width in inches, and then do the same for the height.
Let's use 240 ppi resolution first:
240 pixels per inch x 8 inches wide = 1920 pixels
240 pixels per inch x 10 inches high = 2400 pixels
Total pixels = 1920 pixels wide x 2400 pixels high = 4,608,000 pixels.
Based on the calculation results, we see that in order to print a photo in good quality in an 8 by 10 format, the image must be 1920 pixels wide and 2400 pixels high (or vice versa). A total of about 4.6 million pixels.
We are now starting to approach the limits of the technical capabilities of digital cameras. A 4 megapixel digital camera will no longer be enough for us to be able to print an image in 8 by 10 format with a resolution of 240 pixels per inch. A loss of about 600,000 pixels is not too significant. You'll still be able to print an 8-by-10 image, but you probably won't get professional quality.
Let's do the same calculations for an 8 by 10 format at 300 pixels per inch:
300 pixels per inch x 8 inches wide = 2400 pixels
300 pixels per inch x 10 inches high = 3000 pixels
Total pixels = 2400 pixels wide x 3000 pixels high = 7,200,000 pixels
Now we're really going beyond the limitations of some digital cameras. In order to be able to print an 8 by 10 photo at 300 pixels per inch, our photo would need to be 2400 pixels wide by 3000 pixels high (or vice versa), for a total of 7.2 million pixels! Now that's actually a lot!
This means that you must have at least a 7.2 megapixel digital camera. This way, you'll be able to print your photos in 8 x 10 format and still get professional-quality photos. Of course, don't forget that most photos require at least a little cropping, which means you'll lose a few more pixels.
If you know you'll be printing a lot of 8-by-10 photos, investing in a quality 8-megapixel or higher camera is highly recommended.
That's basically it!
This publication is a translation of the article “ Image Resolution And Print Quality", prepared by the friendly project team
Good bad
12:36 pm - FAQ | What resolution should I set for the photo?So, today's question that I get asked regularly when it comes to saving processed photos to disk:
#16 What resolution should I set for the photo?
We're talking about mysterious dpi, which are often appropriately and inappropriately mentioned by customers in the technical requirements for photographs. But you won’t find something like this everywhere - more often you come across it in program interfaces ppi and no dpi. And customers write and write "send us a photo no less 300dpi!" What is all this and why do photographers need it?
Short version:
In short, this is the density of location:
And, what's most interesting, all these things have nothing to do with raster digital photography until you are going to print it! That is, if you don’t print your photographs (and now there are more such photographers than those who print), then you don’t have to bother yourself with these parameters at all, you won’t need them.
But, just in case, you can set the resolution box to 300. In Lr, for example, this can be done when exporting images, here:
For everyone else, there is a detailed answer. =:)
Expanded answer:
A digital photograph on a computer has only one size characteristic - the number of vertical and horizontal pixels (or their product, now calculated in megapixels). Here is this card, for example:
Has a size of 900 x 600 pixels (or 540,000 pixels, which is equal to 0.54 megapixels). The original frame from which this smaller copy was made was 3600 x 2400 pixels (or 8.64 megapixels). And these values in pixels are the only parameter responsible for the size of photographs in digital form.
Problems may arise when you want to print a photo. Different printing machines and printers, depending on their design and the purpose of the printing result, allow you to create images with different pixel sizes. That is, you can print large pixels and then only a few of them will fit on one inch (about 2.5 cm):
Or you can reproduce pixels of a slightly smaller size and then more of them will fit on one inch:
Or you can make them tiny and then there will be a lot of them on the same linear inch:
As a result, if the same image is taken and printed with different pixel densities per inch ( ppi), then it will have a different size on paper:
It is believed that when more than 300 pixels fit on one linear inch, the human eye is no longer able to separate them, and this gives high-quality, “smooth” printing, without noticeable pixelation. The vast majority of glossy magazines use exactly this (or so) print density, and you can see the result for yourself by purchasing “glossy” printing at any kiosk.
In fact, now the density of 300 ppi is considered a kind of unspoken standard that most publishers focus on. Although, as far as I know, this particular figure does not appear anywhere in the official standards. Well, let me be corrected if I'm wrong.
Moreover, if we are talking about printing, for example, outdoor advertising posters (billboards) big size(3 x 6 meters, for example), then there is no such need to make the pixels microscopic and print them tightly to each other - anyway, viewers will look at the poster from a fair distance, not like at a magazine. Therefore, very often when printing materials for such billboards, a resolution of about 50 ppi is used (there are 50 image pixels per inch of a printed poster).
Ideally, you should know what print density you need and prepare your photos accordingly. If we talk about Ps, then this can be done in the menu item Image -> Image Size:
At the top of this palette we can see the photo size in pixels (3600 x 2400):
And at the bottom - the size in centimeters (127 x 85 cm) with a density of 72 pixels per inch.
These 72 pixels per inch now, in general, look like some kind of spherical horse in a vacuum, because this is a purely rare indicator that is now traditionally assigned to all digital images by default. And it has no real implementation, because someone is now looking at an image on a 15" diagonal monitor with a resolution of 1024 x 768 pixels and it will have the same image density, and someone can look at a 25" monitor with 2560 x 1600 and its density will be different. But it is so traditionally accepted that digital photos are assigned exactly this figure - 72 ppi. "Answer to main question life, the universe and everything - 42!"
By the way, it was not for nothing that Apple engineers described in such detail the advantages of the iPhone4 screens when they first appeared on the market. With a diagonal of 3.5 inches, the image dimensions are 960 x 640 pixels, which gives a resolution of 326 ppi. Which, as you understand, is quite comparable to the quality of good printed printing. And in the future, I am sure that the number of devices with high ppi will grow steadily.
If you uncheck this box:
Then you can see how the image size changes depending on the ppi density (and with the same image size in pixels - 3600 x 2400). At a density of 5 ppi (each pixel will be printed as a 5 x 5 mm square), the image size will be 1829 x 1219 cm:
With a “magazine” density of 300 ppi, the size will already be 30 x 20 cm (almost A4 format, that is, the cover, for example):
At 600 ppi, the photo will take up 15 x 10 on paper (“photo, 10 by 15 with a naive caption...”):
And at 10,000 ppi, the size of this photo will be less than one centimeter on its larger side:
It is clear that printing with a resolution of 10,000 ppi generally makes no sense, especially considering that the threshold at which pixels are visible is considered to be a resolution of 300 ppi.
If you still want to display an image with a resolution of 300 ppi, but on a larger medium, then you will need to turn the checkboxes back on and change the image size in centimeters:
At the same time, please note that the image size in pixels will also increase. This is inevitable, because you want to leave the print density high and you want the size to be larger, which means there will be more pixels in the image. Ps will add the missing pixels, calculating them from neighboring ones. The image quality may suffer noticeably.
Well, what then is it? dpi, which customers love to write about in their image quality requirements? This is the density of dots printed by the output device. And this parameter is purely technical; it can tell a specialist how many dots, for example, a particular printer can print on one inch of an image.
Strictly speaking, dpi not always equal ppi. After all, one pixel of an image must be transmitted by several points on the printing device:
Here we can see that each square (digital image pixel) is represented by several circles of different diameters. Due to them different sizes It turns out to make different color densities, and, as a result, to obtain full-color images with halftones in print. But the printing machine cannot make dots of different sizes; it can only create spots of a certain diameter included in the design. Therefore, the circles we see actually consist of many small dots:
The density of these dots per inch is the parameter, which is denoted as dpi. And if you count, then ppi of this example will be, say, equal to 25, then dpi will be many times more.
But in modern practice It has already happened that in the requirements for photographic quality they often put an equal sign between ppi And dpi. And they come as a result of demands, like "the final image should be 6 x 3 meters in size at 50 dpi", which translated into digital image language means that the picture should be 11811 x 5905 pixels in size. Just like you come across demands like "the image must be at least 3600 x 2400 at 300 dpi", which, as you now understand, does not even look like “oil oil”, but like “square oil”. =:)