Standard photo resolution in pixels. Pixels, Megapixels, Image Resolution, and Digital Photo Print Sizes

Let's get acquainted with some terms that are used in the world of digital photography.

Linear photo size is the width and height of the printed photo in millimeters. The linear size of a photograph can be obtained by measuring it with a regular ruler. For example, the linear size of a 9x13 photograph is 89x127 mm.

Pixels are the dots that make up the image. Just as a mosaic is made up of pieces, a digital photograph is made up of pixels. The more pixels, the finer details can be seen in the image.

Size in pixels is the width and height in pixels of the digital image. For example, digital cameras take pictures of standard sizes 640x480, 1600x1200, etc., and the number of pixels displayed on a computer monitor is 800x600, 1024x768, 1280x1024.

Permission- this is a number that relates the size of the image in pixels and the linear dimensions of the print. It is measured in pixels (dots) per inch (1 inch = 25.4 mm) - dpi (dots per inch). The recommended resolution for printing high quality photos is 300 dpi. Practice shows that the minimum acceptable resolution for printing photos is 150 dpi.

In most cases, you print photos of a standard format 9x13, 10x15, 13x18, 15x20, etc. Each format corresponds to strictly defined linear dimensions. For each format, you can calculate the recommended dimensions of the original image in pixels, so that the resulting print has a resolution of 300 dpi or more.

For example, the linear dimensions of the format 9x13 - 89x127 mm. Multiply the height of the photo (87 mm) by the resolution (300 dpi) and divide by the number of millimeters in one inch (25.4 mm), the result will be the number of pixels in the original image in height

89*300/25.4=1027 pixels.

Similarly for the width

127*300/25.4=1500 pixels.

Thus, for any image larger than 1027x1500 pixels, when printed at 9x13, the resolution will be greater than 300 dpi. In practice, it often happens that a photo with a resolution of 150 dpi looks no worse than the exact same one, but with a resolution of 300 dpi, it depends on what is shown in the photo and from what distance it will be viewed.

When placing an order via the Internet, the system automatically determines which formats are recommended for printing the uploaded photo. If you have chosen a format other than the recommended, then a corresponding message is displayed, while the administration is not responsible for the poor quality of the printed photo.

Table of standard formats and corresponding linear dimensions.

At least three parameters are used to measure the size of photographs - digital image resolution (in pixels), print size (in centimeters) and print resolution (dpi - dots per inch). A user who first encountered the task of converting an image, preparing it for printing is sometimes difficult to figure out these settings, has to act at random and go to the desired result through trial and error, wasting a lot of time and paper.

Let's take a simple example of a problem. You need to take a photo for ID. You can go in two ways - go to a photo studio and take a picture there, paying 150 rubles for 4 small photographs printed on a sheet of 10 * 15 cm. The second option is to take a picture at home, prepare an A4 sheet for printing, on which to squeeze so many of your photos of different sizes that enough for a few years. Then you go to a photo studio and print your creation on an A4 sheet for 30 rubles. It seems that the profit from one order is ridiculous, but if you need to print photos for several people at once (for example, when the whole family is photographed for a visa before traveling to another country), then you can save more money. And this is just one of the examples. Another question is how to keep the dimensions of the photos so that they are exactly 4 * 5 cm on the print (or some other size). In order to adjust the print size to the required one, you need to understand the connection centimeters, pixels and dpi.

Pixels

A pixel is a single dot that makes up an image. A pixel is also called a cell of an image on a monitor or LCD TV. Look closely at the monitor and you will see a barely noticeable grid, one cell of this grid is a pixel. The photo that you downloaded from the camera has a resolution of several megapixels, that is, for example, 6000 pixels wide and 4000 pixels high - this is 6.000 * 4.000 = 24.000.000 pixels or 24 megapixels. When viewed on a monitor, the picture is automatically scaled to the resolution of the monitor (about 2 megapixels). If we try to zoom in (stretch the photo), then to some extent the picture is stretched without a visible loss of quality, but then characteristic squares appear on it. This happens when the actual resolution of the photo is less than what we want to see - the pixel size on the photo has become larger than the pixel size on the monitor.

centimeters

What is "centimeter", I think, it is not necessary to explain. In our case, the size of the prints of a photograph is measured in centimeters. Usually photos are printed in the size of 10*15 cm, but sometimes larger formats are used - 20*30 cm (approximately corresponds to the A4 format), 30*45 cm (A3) and more. You probably faced a problem - you found a beautiful photo on some site and decided to print it in a large format (for example, 20 * 30 cm), but after printing it, you noticed that the print quality is not very good - the object outlines turned out to be a little blurry. The saddest thing is that this photo cannot be corrected by any processing. And all because the resolution of the photo on the site is, for example, 900 * 600 pixels. That is, for 1 pixel on the printout it will have a size of approximately 0.33 millimeters - while it is difficult to count on "ringing" sharpness! And here another image quality parameter appears, with which you can evaluate the quality of the print - DPI

DPI

DPI is an abbreviation for the English phrase Dots per Inch, which translates into Russian as dots per inch. This value just shows how many image pixels fall on one "linear" inch when printed (an inch is 2.54 cm). There is also the value of DPC (dots per centimeter), but it is used less often - whatever one may say, all these printing technologies came to us from where inches, feet, pounds, etc. are in use. So, let's return to our example - a picture of 900 * 600 pixels, which we decided to print in a format of 30 * 20 cm. Let's translate centimeters into inches for convenience - we get 11.8 * 8.9 ". If we divide 900 pixels by 11.8", then we get the print resolution 76dpi. This roughly corresponds to the resolution of the monitor with its "large" pixels, so the picture on the screen looks good. But to get a print of acceptable quality, you need a print resolution of at least 150 DPI, and if you want very good detail, at least 300 DPI. To provide such a resolution when printing 30*20 centimeters, the original digital image must have a resolution of 3540 * 2670 pixels - that's about 9 megapixels. So they found the reason why the photos printed "from the Internet" look blurry and cloudy. Now let's get back to our question - how to adjust the image resolution so that it prints at a given size? As an example, consider the preparation of photographs for documents.

Creating your own photo for documents - step by step instructions

Suppose you need to take some 4*6 cm photos and place them on a 20*30 cm sheet. How to do it?

1. Take the original image, open it in Photoshop. Select the menu item "image" - "image size". We are presented with the following dialog box:

In the dialog that opens, we see two groups of settings - "dimension" and "print size". The "dimension" group displays the dimensions of the digital image in pixels. We do not touch these settings! In the "print size" group, set the size we need in centimeters (the units of measurement are selected from the drop-down lists). In our case, this is 4 * 6 cm. We also set the print resolution to 300 pixels per inch, this will ensure good print quality.

By changing the print size settings, we see that the pixel dimensions also change. That's how it should be! After all this, press the OK button. The image changes in size. Now we need to copy it - use the key combination:

1. Ctrl + A (eng) - select all
2. Ctrl + C (eng) - copy to clipboard

What is copied to the clipboard, we will transfer to a separate canvas, see step 2. 2. Now we need to create a new image that will fit the 20*30 cm sheet that we are going to print to the photo lab. Select the menu "File", "Create", a dialog box appears:

We specify the size of the photo paper on which the printing will be performed (20 by 30 cm) and set the resolution in pixels per inch to be the same as our photo has - 300 DPI. We press OK.

3. An empty image with a transparent background appeared. Press the key combination Ctrl + V and paste our first image on a new canvas. It will look something like this:

The image is pasted as a new layer. Move it to the upper left corner, then select the menu "Layer", "Duplicate Layer".

Another similar picture will appear on the canvas, initially it "lies" on the original layer. We move it and put it next to it. In the same way, we create as many duplicate layers as we need. After that, we perform the flattening of the layers (menu "Layer", "Perform flattening").

We save the picture in JPEG format, copy it to a USB flash drive and go to the photo lab. We tell the operator the following - "print this image with a format of 20 * 30 cm with a resolution of 300 DPI without scaling". At the same time, small pictures will have exactly the size that we indicated for them - in our case 4 * 6 centimeters. It is advisable to have a ruler with you to check the size of the prints.

Resolution (computer graphics)

Permission- a value that determines the number of points (bitmap elements) per unit area (or unit length). The term is usually applied to images in digital form, although it can be applied, for example, to describe the level of granulation of photographic film, photographic paper or other physical media. Higher resolution (more elements) typically provides more accurate representations of the original. Another important characteristic of an image is the bit depth of the color palette.

As a rule, the resolution in different directions is the same, which gives a square-shaped pixel. But this is not necessary - for example, the horizontal resolution may differ from the vertical one, while the image element (pixel) will not be square, but rectangular.

Image resolution

Raster graphics

Resolution is erroneously understood as the size of a photo, monitor screen or image in pixels. Raster image sizes are expressed as the number of pixels horizontally and vertically, for example: 1600×1200. In this case, this means that the width of the image is 1600 and the height is 1200 pixels (such an image consists of 1,920,000 pixels, that is, approximately 2 megapixels). The number of horizontal and vertical dots may be different for different images. Images, as a rule, are stored in a form that is most suitable for display by monitor screens - they store the color of the pixels in the form of the required brightness of the screen emitting elements (RGB), and are designed for the image pixels to be displayed by screen pixels one to one. This makes it easy to display the image on the screen.

When an image is displayed on a screen or paper surface, it occupies a rectangle of a certain size. For optimal placement of the image on the screen, it is necessary to coordinate the number of dots in the image, the proportions of the sides of the image with the corresponding parameters of the display device. If the pixels of an image are rendered 1:1 by the pixels of the output device, the size will be determined only by the resolution of the output device. Accordingly, the higher the screen resolution, the more dots are displayed on the same area and the less grainy and better quality your picture will be. With a large number of points placed on a small area, the eye does not notice the mosaic pattern. The reverse is also true: a small resolution will allow the eye to notice the image raster (“steps”). A high image resolution with a small size of the display device plane will not allow displaying the entire image on it, or the image will be “fitted” during output, for example, for each displayed pixel, the colors of the part of the original image falling into it will be averaged. If you need to display a small image large on a device with a high resolution, you have to calculate the colors of the intermediate pixels. Changing the actual number of pixels in an image is called resampling, and there are a number of algorithms for it of varying complexity.

When outputting to paper, such images are converted to the physical capabilities of the printer: color separation, scaling and rasterization are carried out to display the image with paints of a fixed color and brightness available to the printer. To display colors of different brightness and hue, the printer has to group several smaller dots of the color available to it, for example, one gray pixel of such an original image, as a rule, is represented in print by several small black dots on a white background of paper. In non-professional prepress applications, this process is performed with minimal user intervention, according to the printer settings and desired print size. Images in prepress formats and designed for direct output by a printing device need to be converted back to be fully displayed on the screen.

Most graphics file formats allow you to store data about the desired scale when printing, that is, the desired resolution in dpi (eng. dots per inch- this value indicates a certain number of dots per unit length, for example 300 dpi means 300 dots per inch). This is purely a reference value. As a rule, to obtain a printout of a photograph, which is intended to be viewed from a distance of about 20-30 centimeters, a resolution of 300 dpi is sufficient. Based on this, you can estimate what size print can be obtained from the existing image or what size the image needs to be obtained in order to then make a print of the desired size.

For example, you need to print an image with a resolution of 300 dpi on paper measuring 10 × 10 cm. Converting the size to inches, we get 3.9 × 3.9 inches. Now, multiplying 3.9 by 300, we get the size of the photo in pixels: 1170x1170. Thus, to print an image of acceptable quality with a size of 10x10 cm, the size of the original image must be at least 1170x1170 pixels.

The following terms are used to indicate the resolution of various image conversion processes (scanning, printing, rasterization, etc.):

• dpi (English) dots per inch) is the number of dots per inch.
• ppi (English) pixels per inch) is the number of pixels per inch.
• lpi (English) lines per inch) - the number of lines per inch, the resolution of graphics tablets (digitizers).
• spi (English) samples per inch) - the number of samples per inch; sampling density ( sampling density), including the resolution of image scanners (en:Samples per inch English)

For historical reasons, values ​​tend to be reduced to dpi , although from a practical point of view, ppi more unambiguously characterizes printing or scanning processes for the consumer. Measurement in lpi is widely used in the printing industry. A dimension in spi is used to describe the internal processes of devices or algorithms.

Color bit depth value

Color is sometimes more important than (high) resolution in creating a realistic image using computer graphics, because the human eye perceives an image with more color shades as more believable. The type of image on the screen directly depends on the selected video mode, which is based on three characteristics: in addition to the actual permissions(number of dots horizontally and vertically), the image refresh rate (Hz) and the number of displayed colors (color mode or color bit depth) differ. The last parameter (characteristic) is often also called color resolution, or resolution frequency (frequency or gamma bit depth) colors.

There is no difference between 24-bit and 32-bit color by eye, because in the 32-bit representation 8 bits are simply not used, facilitating pixel addressing, but increasing the memory occupied by the image, and 16-bit color is noticeably “rougher”. For professional digital cameras with scanners (for example, 48 or 51 bits per pixel), a higher bit depth is useful in the subsequent processing of photographs: color correction, retouching, etc.

Vector graphics

For vector images, due to the principle of image construction, the concept of resolution is not applicable.

Device Resolution

Device resolution ( inherent resolution) describes the maximum resolution of an image received by an input or output device.

• Printer resolution, usually indicated in dpi.
• Image scanner resolution is specified in ppi (pixels per inch), not dpi.
• Monitor screen resolution is usually referred to as the dimensions of the image received on the screen in pixels: 800 × 600, 1024 × 768, 1280 × 1024, meaning the resolution is relative to the physical dimensions of the screen, and not to a reference length unit such as 1 inch. To obtain resolution in ppi units, this number of pixels must be divided by the physical dimensions of the screen, expressed in inches. Two other important screen geometric characteristics are its diagonal size and aspect ratio.
• The resolution of a digital camera matrix, as well as a monitor screen, is characterized by the size (in pixels) of the resulting images, but unlike screens, it has become popular to use not two numbers, but a rounded total number of pixels, expressed in megapixels. We can talk about the actual resolution of the matrix only considering its size. We can talk about the actual resolution of the resulting images either in relation to the output device - screens and printers, or in relation to photographed objects, taking into account their perspective distortions during shooting and lens characteristics.

Monitor screen resolution

For typical resolutions of monitors, indicator panels, and device screens ( inherent resolution) there are well-established letter designations:

see also

Notes

Size, resolution and formats... What happens to the pixels? Do you buy a camera because of the number of megapixels? Are you having trouble posting photos online? Do your photos print in poor quality, even if they look great on the 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 analyze this extremely important information for any photographer.

So let's go over some basic concepts to make your life easier and your workflow more efficient and your images to be the right size for their intended use.

This is a 750×500 pixel image with a resolution of 72 dpi, saved in compressed JPG format, which is 174kb. Let's figure out what it all means.

Are resolution and size the same thing?

One of the biggest misunderstandings comes from the concept of permission. If this is your case, trust me you are not alone.

The problem is that permission can refer to many things, two of which can be a problem. I'll explain these two resolution concepts next, but they have one thing in common that I need to clarify first. Both of them 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 most understandable and "essential" specs on the market, so I'll start with that.

What is a pixel?

Digital photography is not one inseparable thing. If you zoom in close enough, you'll see that the image looks like a mosaic of tiny tiles called pixels in photography.

The number of these pixels and the way they are distributed are two factors to consider in order to understand what resolution is.

Number of pixels

The first kind of resolution refers to the number of pixels that make up your photo. To calculate this resolution, you simply use the same formula that 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. Because this number is very impractical, you can just divide it by a million to convert it to megapixels. So 13,500,000/1,000,000 = 13.5 megapixels.

Pixel Density

The other resolution is how you distribute the total number of pixels available, which is commonly referred to as pixel density.

Now resolution is expressed in dpi (or ppi), which is an abbreviation for dots (or pixels) per inch, yes, per inch, it so happened that this was not translated into the metric system. 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 it to 300 dpi, but at 72 dpi it will be 62.5 x 41.6 inches. Although the size of the printed image changes, you don't change the size of your photo (image file), you just change the organization of the existing pixels.

Imagine a rubber band, you can stretch it or shrink 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 quantity means 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, in addition to the amount, you also have to consider 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, 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 will 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 what 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 there is more information in each pixel. That is why quality and quantity are not necessarily identical.

Therefore, the quantity matters, but the size and depth of each pixel determines the quality. That's why you should look at all the specs of the camera and its sensor, not just the number of megapixels. After all, there is a limit to the size you can print or view, moreover, it will only result in additional file size (megabytes) and will not affect image size (megapixels) or quality.

How to choose 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 a resolution of just 72 dpi, but that's way too low for a photo print. If you are going to print, you need 300 to 350 dpi.

Of course, we're talking in general terms because each monitor and each printer will have slightly different resolutions. For example, if you want to print a photo up to 8×10 inches, you need the image to be 300dpi x 8" = 2400px and 300dpi x 10" = 3000px (so 2400×3000 to print 8×10 at 300 dpi). Anything more 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 box "resample". If you don't enable "resample", you will be remapping pixels as I explained at the beginning of the article.

You can also select the "Proportion" checkbox if you want the parameters to be adjusted according to your changes. So the width changes when the height changes and vice versa.

8×10 inches at 300ppi, this is the size needed to print 8×10. Note the pixel size of 3000x 2400.

750×500 pixels at 72ppi. This is web resolution and is the exact size of all images in this article. Size in inches doesn't matter when publishing to the web - only pixel size matters.

At the top of the window, you will also see how the file size changes. This is the uncompressed version of your image, which is the direct link I talked about in the first part of this 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? If you choose very low quality, you run the risk of degrading the image too much.

Conclusion

So that's what quality, quantity, size, and resolution mean, and they're all related to pixels, since those are the basic units that make up an image. Now that you know how to make the best choice for printing, sending and storing your photos. All this information is laid out in more detail in the video course: "Secrets of Creative Photo Editing for a Beginner", to get acquainted with the description of the course, click on the picture below.

Quite often, you need to find out the size and weight of photos that are stored on a computer, on a flash drive or any other medium (including a website on the Internet). There are a lot of ways to do this and it is simply impossible to describe them all. I propose to consider 6 ways to find out the size of a photo in pixels and centimeters- on a computer, using Windows tools, in Photoshop and Bridge programs, using a free program for photos of any format, and using browsers for photos on websites.

1 | Find out the size of a single photo (on Windows):

The quickest way to look at the file's properties is to right-click on the photo and select Properties from the list. On the first tab General (General) you can see the weight of the photo in megabytes (MB) or kilobytes (KB). To find out the size of the photo in pixels (px), you need to go to the Details tab and, if necessary, scroll down to the Dimensions line.

2 | How to quickly find out the size of multiple photos (in Windows):

Open the photo folder you need and add the Details panel in the View tab. As a result, by clicking on any photo, detailed information about the file will open in a separate panel. In different versions of Windows, the display settings panel may look different, but the meaning and result will be approximately the same.

3 | How to quickly find out the size of all photos in a folder (in Windows):

Change the file display format - open the photo folder you need, in the View tab, select the Details format for displaying files and add the Dimensions column, as shown in the picture below. Now you can see the size, weight and format of all photos in the folder. Approximately the same effect can be achieved by selecting the display format Content (Content).

4 | How to find out the size of a photo in centimeters:

Photos on computers, flash drives and any other electronic media (including websites on the Internet) are stored in pixels. Centimeters are needed for printing photos. The maximum possible size in centimeters for high-quality printing of a particular photo will depend on:

• print file size (in pixels),
• on the quality of the photo (degree of file compression, the amount of noise and other artifacts),
• on the capabilities and settings of the printer - on the print density (how many pixels per inch or centimeter the printer prints).

To find out the size of a photo in centimeters, you will need Adobe Photoshop, Adobe Bridge or any other photo editor. To find out the file size in Photoshop, you need to press the key combination ALT + CTRL + I or in the top panel go to Image (Image) Image size (Image size).

In Photoshop, you can change the resolution, size in pixels, and see on the fly how the size of the photo changes in centimeters (or inches).

In Adobe Bridge, the photo size in pixels and centimeters can be seen in File Properties. If you do not have this section or the "Resolution in centimeters" line, you need to enable their display. To do this, go to the top menu Edit Preferences and in Metadata add checkboxes to the lines Dimensions, Dimensions (in cm), Resolution (pixel density).

5 | How to find out the size of a photo on the site:

It is most convenient to use the Mozilla Firefox browser, where you can right-click on any picture and select "Image Information". In the window that opens, the image itself will be shown, original and resized for display on the site.

Many people use the Google Chrome browser (Google Chrome), in which everything is a little more complicated.

In the Google Chrome browser, you need to right-click on the photo on the site and select "View code" (in the Yandex browser, you need to select "Explore element"). If you move the mouse over the selected fragment of the page code, a window will appear with information about the size of the photo on the site.

6 | How to find out the size of a RAW photo:

Not all programs can see and read RAW files (which I wrote about in the article Size, Weight and Photo Format). To find out the size of a RAW photo, you can use Adobe Photoshop, Adobe Bridge, or Adobe Lightroom. A convenient free program that can open and read almost all photo formats (including RAW) - FastStone Image Viewer. It can be downloaded from the developer's website (faststone.org) and used completely free of charge. This program is the sixth way to quickly find out the size of a photo in pixels (and for some photo formats, including jpg, find out the size of a photo in centimeters).