Lesson: image resolution. Pixels, resolution and printing of digital images

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 look at some basic concepts to make your life easier and your workflow more efficient and your images will have right size for the 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. Next, I will explain these two permission concepts, however they have one common feature which I need to clear up 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. 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

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 for an 8×10 print 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 than less value you install, 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 the best choice to print, send and store 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.

Pixels, Megapixels, Image Resolution, and Digital Photo Print Sizes

The quality of a digital photograph largely depends on the number and size of pixels contained in the image. The resolution of an image is simply information about the pixels and their density in an image. In this article, you'll learn about how pixels and photo resolution affect how images look on a computer screen or when they're printed.

What are pixels?
The word pixel is an abbreviated version of the combination English words"image" and "element" (Picture, Element). Digital cameras have image sensors with millions of photosensitive elements. Each of these trace elements that capture light is called a pixel.
For example, the Nikon D5100 digital SLR has a larger sensor image sensor than, for example, the Canon Powershot ELPH 300 HS compact digital camera. The larger the sensor, the more pixels it contains and the better the images it reproduces.
The color and light intensity of each of the millions of individual pixels blend (align) into a single image when we view them as a printed image on a printer or computer screen.

Photo file size
The file size of a photo expresses the total number of pixels in the width and height of the image. For example, the file size can be written as 3456x2304. This would mean that there are 3456 pixels in each row of the image (from left to right) and 2304 pixels in each of its columns (from top to bottom). For reference, 1 million pixels equals 1 megapixel.
To find the total number of pixels in an image, simply multiply the number of pixels in the image's width by the number of pixels in its height (3456 x 2304 = 7962624). Generally, the total number of pixels is rounded up or down to the nearest whole number of megapixels. So in this case, the image can be called an 8-megapixel picture, although it does not contain the full 8 million pixels.
If the number 7,962,624 represents the maximum file size the camera can play, then the manufacturer will sell the camera as an 8-megapixel camera.
While digital cameras are often marketed with a focus on the total number of megapixels available in an image, they all have settings that allow the photographer to capture images with a smaller file size. These settings save space on the camera's memory card or computer hard drive.

Also, images with a smaller file size are easier to send and download when using Email. Taking pictures with different file sizes will become more understandable and make more sense to you once you become familiar with concepts such as image resolution and print size.

Image Resolution

In general, image resolution in digital photography is the amount of information contained in an image file. This information is the number of pixels contained in any digital image you make. An image file of 4000x3000 pixels will have a higher image resolution than a 2000x1500 image file. Higher resolution photos will be sharper, brighter and more accurately reproduced when printed or viewed on a computer screen.

From a technical point of view, the resolution of an image corresponds more to the density, expressed in terms of PPI - (Pixels per Inch) the number of pixels per inch or dots per inch DPI (Dots per Inch), rather than the size of the entire file. Sometimes the terms PPI and DPI are often incorrectly used interchangeably. In this article, we will use the term PPI to refer to the resolution of a photo on a computer screen. When we talk about the resolution of photographs printed using, for example, an inkjet printer, we will use the term DPI. We will discuss in more detail all the technical differences between these terms in another article.

Image resolution is usually written as a number, such as 72 PPI, or 300 DPI. This means that this image file contains 72 pixels or 300 dots per square inch of its area. This will be 72 pixels or 300 pixels from left to right and top to bottom for every inch of this file. This information becomes important when it comes to how your photos will be displayed.

Computer monitors are capable of displaying sharp and high-contrast images at low screen resolutions such as 72 or 96 PPI. If you intend to take pictures that will only be displayed on the monitor, you can set the camera to low level picture quality, such as one megapixel or less. Shooting at high quality settings, such as 12 megapixels, does not make the photo look best on a 72 PPI monitor. However, you should definitely set your camera to a higher image quality if you are going to print large-format photographs on a printer.

Calculating Maximum Print Sizes
As mentioned earlier, in order to view photos in clear quality on a computer monitor, it only needs to have an output resolution of 72 or 96 PPI. However, in order to produce sharp and high-quality photo prints, the output resolution of the printer must be much higher. Printer output resolution from 140 dpi to 300 dpi is the best range for creating quality prints of your photos. (300 DPI prints are already professional-grade prints.)

File size Megapixels Maximum Maximum
(pixels) print size print size
at density at density
@200 DPI @300 DPI

1600x1200 2 8.0x6.0 5.3x4.0
2048x1536 3 10.2x7.60 6.8x5.1
2592x1944 5 12.9x9.70 8.6x6.4
3072x2304 7 15.3x11.5 10.2x7.6
3264x2448 8 16.3x12.2 10.8x8.1
3648x2736 10 18.2x13.6 12.1x9.1
4000x3000 12 20.0x15.0 13.3x10
4288x3216 14 21.4x16.8 14.2x10.7

The chart above will give you a general idea of ​​the maximum possible print sizes (in inches) that you can enlarge your photos to while still maintaining good quality. Please note that the maximum size of the prints listed can be increased to slightly larger sizes than those indicated above. However, a 3-megapixel photo enlarged to 16x20 inches will already be of very poor quality when printed. Making prints smaller than the recommended maximum sizes for the files listed in the table is not a problem. The print will still be of very high quality.

Some of the most commonly used photo print sizes are 4X6, 5x7, 8x10, 10x13, 11x14 and 16x20. (These dimensions are for photographs taken with the camera held vertically, while the dimensions in the table are for photographs taken with the camera held horizontally.)

It's actually quite easy to determine the maximum print size for your digital photos. First of all, you need to determine how many DPI (dots per inch) will be used when printing a file. For simplicity, let's assume that the output printer resolution is 200 dpi. If your image file size is 2000x1600 pixels, then you can get a quality 10x8 inch print of it.

The math is to divide the number of pixels in the file width by the 200 DPI printer resolution (2000/200 = 10). Then divide the number of pixels in the height of the file by 200 (1600/200 = 8). This completes the calculation. A 2000x1600 pixel file can be printed into a photo good quality size 10x8 inches, with an output print density of the printer 200 DPI.
If you choose to print at 300 DPI from the same image file, you will get a higher resolution print. However, the maximum size for a quality print will be smaller. Let's calculate: 2000/300 = 6.6. Further, 1600/300 = 5.3. So if we round the figures obtained, then the maximum standard size for printing will be about 5x7 inches.

Of course, you don't have to do this calculation every time you take a picture. Just keep in mind that when you plan on taking pictures that will be printed out on a large-size printer, set your camera to shoot in a larger file size.

hadson

The calculators in this article focus on the topic of digital photo printing.

The first calculator helps you choose the photo format for printing an image known sizes. Let's formulate the task.

Given: We have a digital image of known sizes, for example, 3264 by 2448 pixels, and a set of standard formats offered by photo printing services. The format defines linear dimensions photographs, for example, a 10x15 photograph has dimensions of 102 by 152 millimeters.

Required: Choose from a set of formats as large as possible, on which you can still print an image without losing quality.

To set photo formats, I created a separate Photo Formats guide, which can be expanded if necessary.

The only specialized knowledge you need to have in order to find the answer is the knowledge that high-quality digital image printing requires a resolution of at least 300 dots (pixels) per inch (300 dpi), and more or less acceptable printing is possible at a resolution of at least 150 dots per inch (300 dpi). inch (150 dpi). Everything else is simple math.

Graphically, the task is shown in the figure below.

The logic for finding the answer is simple - the linear dimensions of each format are converted to inches, and then to pixels, based on the fact that there are 300 (150) pixels in one inch. Next, the resulting number is compared with the image size (there are certain nuances associated with the ratio of height and width, but more on that in the second part). If the size of the format in pixels is larger than the size of our image (in the figure - the format is to the right of the photo), then it will no longer work, because the photo will have to be stretched, and we will get a resolution worse than 300 (150) dpi. If the size of the format is smaller than the size of our image (in the figure - the format is to the right of the photo), then it will work - the photo will have to be compressed, and we will get a resolution better than 300 (150) dpi.

Of all the suitable formats, the calculator selects the maximum size format (there is no problem with printing smaller images - as far as I understand, you can also print with a resolution of 1200 dpi).

Format size in pixels for 300 dpi resolution

Format size in pixels for a resolution of 150 dpi

The second calculator for the size of the already printed image and the size of the original image helps to determine the resulting image resolution and the part cropped when scaling. Let's formulate the task.

Given: An image of known dimensions is printed on an image of known dimensions. Since the value of the ratio of the height and width of the image and the value of the ratio of the height and width of the digital image, as a rule, do not match, when printing, the image is scaled, obviously, while maintaining the proportions. Graphically, this is shown in the figure below.

When scaling, as you can see, two options are possible:
the first is scaling with the loss of part of the image,
the second is scaling while preserving the entire image, but with the appearance of an empty space in the image.
As an aesthete, I chose the first option for calculations.

Thus, the first thing that is required is to find the resulting image resolution and the part of the image that was not included in the image. The second, respectively, will be the difference between the used width (height) and the original width (height) of the image.

Width of the printed image, cm

Height of the printed image, cm

Image width in pixels

Pixel(Pixel) – The smallest element of a two-dimensional image in a raster graphic.

Each smallest element has its own color, brightness and possibly transparency.

Let's see how it looks under magnification pixel grid».

The example uses an image that is available.

The number of pixels determines the level of accuracy, detail of the image (photo), and the resolution value.

The number of pixels is related to the amount of megapixels in the camera settings.

If the camera has 18.7 -megapixel camera, the maximum size will be 5184 X 3436 , which means the photo will have 5184 pixel wide and 3436 in height.

Permission

Image pixel size measures the total number of pixels across the width and height.

Permission(Resolution) - a value that determines the sharpness of the details of the bitmap. Most often it is set in pixels per inch (Pixels Per Inch / PPI).

The more pixels per measure, the higher the resolution.

The higher the resolution, the better the print quality.

Note

In Photoshop, you can look at the ratio of the size and resolution of an open image by going through the "" menu ( / Keyboard Shortcut " Atl+Ctrl+i»).

Let's look at the difference in permissions as an example.

Below is 2 photo options with different resolutions.

When creating a document in Photoshop ( File - Create| / Keyboard shortcut " Ctrl+N”), you can set the parameter “ Permission» (Resolution).

We examined the concepts of "pixel" and "resolution" in relation to bitmap images and Photoshop.

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Raster is an image consisting of an array of dots - pixels. A pixel is an elementary, that is, the smallest and no longer divisible element of a two-dimensional digital image of a rectangular or round shape of a certain color. At the same time, a pixel is also a physical element of the matrix of output devices - displays. For example, on a plasma panel monitor, the pixel may be octagonal.

Thus, with the help of such colored dots-pixels, you can create a picture of almost any complexity. Raster format represents images on most graphics output devices: monitors, scanners, printers, cell phones, digital cameras.

The size of a bitmap is the width and height of the drawing in pixels. For example, if we right-click on the picture on this page, we open the context menu and go to "Image Properties ...":

then we will see its dimensions in pixels, where 200 is its width, and 150 is its height:

The number of pixels per unit length is the resolution of the image. The higher the resolution, the more pixels per inch. The smaller they will be. And the more clear the details of the image will be, the more accurate the display of the original will be. Resolution is measured in dpi (dots per inch) - the number of dots per inch.

For a printed photo of normal quality, a resolution of 300 dpi is sufficient. Based on this, it is easy to calculate the size of a digital image in pixels for a certain photo paper format. For example, to fit a photo into A4 (210x297) mm or 8x11 inches, we multiply 8 by 300 and 11 by 300. And we get 2400x3300px. This should be the minimum image size for printing on A4. If the dimensions are smaller, then the image will be fuzzy, blurry.

Now let's move on to the resolution of the monitor. Resolution determines the clarity of pictures and text on the screen. At high resolutions, objects become smaller, appear sharper, and appear larger on the screen. At low resolution, on the contrary, objects look larger and there are fewer of them on the screen.

Cathode ray tube (CRT) monitors, which are no longer used anywhere today, can work effectively in a variety of resolutions. Liquid crystal displays and desktop and laptop monitors based on them are best used at native resolution. Native is the resolution for which the monitor is designed based on its dimensions.

Monitors by aspect ratio are standard 4:3 or widescreen with 16:9, or 16:10. This means that for every four units of screen width, there are three units of height. Or 16 units horizontally with nine units vertically.

LCD monitors have a number of advantages over CRTs. It is compact and light weight. No flicker related to frame rate. No geometric distortion of the image. The high definition of the picture is a consequence of the higher resolution. LCD monitors do not emit electromagnetic waves and are therefore safer. Modern widescreen monitors are available even with a built-in audio system.

Right-click anywhere on the desktop to open the context menu and select the "Screen resolution" line. The Display Settings window will open. Here we expand the "Resolution" scale:

1920x1080px is the native resolution of this 24-inch display. 24 inches is its diagonal. To find out the dpi, you need to divide 1920 pixels by the width and 1080 pixels by the height of the screen in inches. And we get 92dpi. For comparison: a 15-inch CRT monitor is considered optimal resolution of 800x600px, which is 67dpi.

From here - practical conclusions. When we select beautiful wallpapers for the desktop, the size of the picture in pixels should not be less than the set monitor resolution. For example, for the 24-inch monitor shown above, the dimensions of the picture should exceed 1920px horizontally and 1080px vertically. Or be exactly the same size. A smaller image will look blurry and completely unacceptable.

Wallpapers and various images can be selected on a specialized image search engine. An active link is on the page of Internet search engines.

The disadvantage of simple raster images is the large size of the image file. Therefore, raster photographs and drawings are saved in a compressed form in various graphic formats. The choice of format depends on the type of image and how it is used. Optimal for posting full-color photos on the Internet is the jpeg format, for example. However, jpeg is not well suited for drawings, character and text structures. Such graphics are best saved in formats that compress losslessly, like png or gif.

There is much more to write about graphic formats.

And, how easy it is to make a gif-animation yourself - we read the “gif” in the article