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How to calculate the correct image size and resolution for printing and displaying on the screen

One of the most confusing things for a new photographer can be understanding the difference between file size and resolution for printing or displaying on a monitor. In this article, photographer Helen Bradly helps you figure it out and shows you how to resize images depending on what you want to do with them: print or display on the screen of an electronic device
. Let’s start.

What is the resolution of digital cameras?

When it comes to digital cameras, resolution refers to the number of megapixels produced by the image sensor. This in turn usually corresponds to the amount of detail the camera can capture. So if your camera has 20 megapixels (often referred to as 20 MP), it will capture less detail than a 30 megapixel camera, which in turn will capture less detail than a 40 megapixel camera. But what is a megapixel, really? ? And how does this affect your ability to print and display photos?

Megapixels and photo size

Как рассчитать правильно размер и разрешение изображения для печати и отображения на экране

Technically, a megapixel is equal to 1,048,576 pixels; in fact, camera manufacturers round this number to the nearest 1,000,000 when talking about what image size the camera will capture.

Helen’s camera, for example, captures 14.6 megapixel images, which is about 14,600,000 pixels per image (14.6×1,000,000). This information doesn’t tell you anything about the actual pixel dimensions of the image, it only tells you the total number of pixels that make up the image.

Its camera, like most DSLRs, shoots images with an aspect ratio of 1.5. Thus, the ratio of the number of pixels along the long edge of the image to the short edge of the image is 3:2.

Each of the full-size RAW images
photographer has a size of 4672×3104 pixels. So, by multiplying the number of pixels in the width of the image by the number of pixels in the height of the image, we get the actual number of pixels in the image (4672×3104 = 14,501,888). We could call it 14.5 MP, but camera manufacturers have rounded up the number and call such a camera 14.6 MP.

You can check the width and height of the image using photo editing software. In Photoshop, you can open an image, then choose File > File Info > Camera Data. The image above shows the dialog box with the information received.

So, a pixel itself is a single element of an image – and for our purposes, it is the smallest element into which a photograph can be divided. A pixel can only be one color, but a photograph is made up of a grid of thousands of pixels, each with a different color, that together make up the final image. You can see the pixels if you open the photo and zoom in until you see individual blocks of color (as shown below). Each of these blocks represents a separate pixel.

Как рассчитать правильно размер и разрешение изображения для печати и отображения на экране

Why size is important when printing

When printing images, photographers come across the term PPI/DPI or pixels per inch. D PI refers to the number of dots contained in one inch of an image printed on paper by a printer. P PI refers to the number of pixels contained in one inch of image displayed on a computer monitor. Most print services and your own printer will require a certain pixel density in the image (PPI) to be able to print a photo that looks good (that is, with smooth color transitions so you don’t have to look at every single pixel).

Typical print PPI values ​​range from 150 to 300 PPI, although some high-quality magazines may require 1200 PPI images. So, for example, if you want to print a 4×6-inch image at 300 pixels per inch, you’ll need a file that is at least 4×300 (1200) pixels on the short side and 6×300 (1800) pixels on the long side. In other words, it must be at least 1200×1800 pixels in size.

To print an 8×10 inch image at 300 PPI, use the same math.

Multiply the width and height of the printed image in inches by 300 pixels. The result is 2400×3000 pixels, which is the image resolution needed to print an 8×10 image at 300 pixels per inch. So when cropping and resizing an image for printing, you need to know what the PPI of the image should be. This should be stated in your printer manual or printing service.

Below is a screenshot from the website showing the optimal and minimum image sizes for standard print sizes. The printer prints them
at 250 PPI (but can handle 100 PPI images), although other services may vary, so always check before preparing images for printing.

Use the crop or resize function in your software to resize the image to the desired width and height and desired PPI resolution.

Here, an image cropped to 3000×2400 pixels is adjusted from 72 PPI to 300 PPI in preparation for printing at 300 PPI. No resampling is required since the image is already at the correct dimensions and only resolution is required.

Как рассчитать правильно размер и разрешение изображения для печати и отображения на экране

Photoshop, like other applications, will also crop an image to a fixed size and resolution if you enter the desired values ​​in the Options Bar when you have the Crop Tool selected (see below). If your image is smaller than the specified dimensions, it will be enlarged using the default resampling method. While it is generally not recommended to enlarge images, provided the image is already close to the desired size, enlarging it slightly usually does not cause a noticeable loss in quality.

Как рассчитать правильно размер и разрешение изображения для печати и отображения на экране

Fit to screen

When it comes to displaying images on screen, you need far fewer pixels than when printing. This is because the pixel density on the screen is much less than what is required for printing. For example, the size of a regular FullHD monitor is 1920×1080 pixels. To fill your monitor, you only need a 1920×1080 pixel image. This is about the same image size needed for a 4×6 print at 300 PPI, but still displays a 1920×1080 pixel image perfectly on a 23-inch monitor.

How to reduce the size of a photo for posting on the Internet

Probably many have encountered the fact that they cannot upload photos to a website on the Internet, because photographs taken on a modern digital camera are always large in size and are not very suitable for uploading to the Internet without additional processing, i.e. reducing them. Therefore, we need to reduce the size of the photo.

There are a huge number of graphic editors such as Photoshop, with which you can easily do this. But if these programs are not at hand, then we will use the Paint program, which is usually already installed with the system along with Windows.

To do this, right-click our photo file, a menu opens: left-click “open with”, another menu opens: select the Paint program from the menu. So our photo is opened in the Paint program.

(By the way, you can do it differently: first open the Paint program, then in the top menu File -> Open, look for our photo on the computer and open it.

) Then, in the top menu, left-click “Drawing” and then in the “Stretch/Tilt” menu that opens, or instead press two Ctrl W buttons on the keyboard at the same time and the “Stretch” and below “Tilt” settings open. We need to work with the “stretch” settings.

If we are not satisfied with this reduction, then in the top menu click “Edit”, then cancel, or instead press two “Ctrl Z” keys on the keyboard at once and all your changes in the photo size will be canceled, i.e. e. The photo will be the same size. And now we first begin to substitute numbers in percentages in the “horizontal” window and in the “vertical” window. (It is imperative to put the same numbers in these windows, otherwise the image in the photo will be distorted.)

After the next attempt, when you are satisfied with the photo size, then in the top menu click “File” then “Save As”. A file save window pops up.

Here you need to specify the “file name” (in Latin letters or numbers) and the file type at the bottom of the window; for the Internet, “JPG” or “JPEG” is usually suitable. Then click the “Save” button on the right, after remembering in which folder on the computer you saved your photo.

Open this folder on the computer, find this photo, which has decreased in size, and upload it to the website on the Internet.

The above describes how to reduce a photo on your computer, but this can also be done below in the program: To do this, click Upload image from computer, select the image and click open. Now your photo is in the program and you can work with it, in this case we need to reduce the size.

Click in the top menu Image -> Image Size. In the plate, reduce the width or height of the image, for example, set the width to 900 and the height will decrease accordingly (the Keep proportions checkbox should be checked. Click Yes and the photo will be reduced in size.

Then in the top menu click File -> Save, in the window that appears you can slightly change the image quality, but it is better to leave the default 80, leave the format as JPEG, the file name can be left as is or renamed in Latin letters or numbers, but always in add .jpg to the end of the file name (for example, let’s call the file fotka.

jpg) and then click Yes and save the reduced photo on your computer, which you can then easily upload to a website on the Internet.

In addition to reducing the photo in this program, you can change the brightness, color, contrast of the photo, and apply many special effects.

If anything is unclear below, ask questions in the comments.

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Review of popular photo formats for printing

There are generally accepted international ISO formats that define standard sizes for photographic paper. However, terms such as A3, A4, Whatman paper, etc. have become more familiar to us. The aspect ratio of the main photo formats is similar to the matrices of modern digital cameras and is 1: 1.5 (2/3) or 1: 1.33 (3/4), and standard international paper sizes are 1: 1.4142.

We invite you to familiarize yourself with the table, which shows the main photo formats for printing.

Основные форматы фото для печати

Let’s take a closer look at the main options and compare them with standard ISO formats.

Соотношение формата A4 и фото 10х15

One of the most popular photo formats for printing is 10×15. It differs from the standard A6 in that it is 2 mm smaller on one side and 5 mm larger on the other. This is perhaps the most common format and is suitable for almost all photo albums and frames. The photo shows how the 10×15 image compares to A4 photo paper.

Соотношение формата A4 и фото 15х21

An equally popular photo size for printing is 15×21. The photo is slightly larger than A5. The difference is very small: on one side the difference is 5 mm, on the other – 1 mm. Vertical photographs are ideal for creating portraits.

Соотношение формата A4 и фото 20х30

The photo format for printing 20×30 is close to A4, the difference is that on one side the image is 6 mm smaller, on the other – 9 mm larger. The peculiarity of photographs of this size is high detail and clarity. That is why images are often used to create posters, which are an excellent interior decoration.

Соотношение формата A3 и фото 30х40

Using a 30×40 photo for printing is an excellent option for creating a highly artistic wall composition. The difference between the format and A3 is that on one side and the other the image is larger by 9 mm and 1 mm, respectively. Photographs are often placed in a wooden frame or stretched on a stretcher.

Соотношение формата A3 и фото 30х45

Photo format for printing 30×45 is one of the favorites among users of the Mimigram application. This size is ideal for making posters
. The printed images are incredibly clear and colorful. That is why posters are often used to organize photo exhibitions. The format is slightly larger than standard A3.

Photo optimization for the web

I don’t presume to say that what is stated in this article is the only correct way to optimize images.

Everything that is stated below is just a determination of the direction in which direction to move at first, and then everyone will make their own choice. So, open Photoshop, process the photo, enter copyright information, etc.

d. (look for the copyright information window in the File menu > File information > Description), see Fig. 10

In the window that appears, check the boxes as shown in the photo below.

After this, you need to set the resolution. I usually set it to 96 or 72.

To set the necessary geometric parameters of a photo, just enter a numerical value in any of the dimension columns, since if you check the box to save proportions, another parameter will change automatically.

I usually set the width from 800 pixels to 1000, since this is the optimal file size at which the quality and weight of the photo are most balanced. Many photo resources do not accept photos weighing more than 250 Kb.

Therefore, it is necessary to choose the optimal file size, which will not affect the quality of the image.

We leave the interpolation as bicubic (by default).

After clicking the Ok button, we return to the photo, which has become much lighter in weight and smaller in size. By setting the scale to 100%, we can see the real size of the photo that guests of your page on the Internet will soon see.

To optimize the photo, go to the “File” menu, in the drop-down menu select “Save for Web and devices…”

Our photo appears in the window that opens, which we will optimize for web pages. First, select the file format, in this case Jpeg. The optimization method is “Optimization”, although you can choose the “Progressive” method.

With the usual “Optimization” method, the file is opened immediately in normal quality, but not all at once, but gradually from top to bottom (line by line). It all depends on the speed of the Internet; the higher the speed, the faster this process occurs.

After choosing the optimization method, we move on to correcting the weight and quality of the photo. Use the “Quality” slider to set the photo quality that is most acceptable to you. Here I set it to 85, since the quality I selected fits into 234 Kb., which is quite enough… The download speed from the server was 43 seconds at a rather low Internet speed – 56.6 kbps.

By calling the “Select download speed” menu, you can select any of the download speeds available to you, but remember that not everyone today has an Internet speed of 2Mb/s.

If there is a need for additional correction of photo parameters, the “Image Size” panel has tools already familiar to us…

To let the world know what camera you are using and what settings you use when shooting, select the “All” item in the “Metadata” panel.

I hope I spoke in sufficient detail about the optimization process, if not, leave your questions in the comments. Good luck!

Photo size chart for printing

Standard photo sizes for printing are presented in the table:

Standard photo Size (pixels) Exact size Number
9×13 1063×1535 8.90×12.70 1
10×15 1181×1772 10.20×15.20 2
13×18 1535×2126 12.70×17.80 3
15×20 1772×2362 15.20×20.30 4
15×21 1772×2362 15.20×21.60 5
15×22 1772×2480 15.20×22.80 6
15×30 1772×2598 15.20×30.00 7
15×38 1772×3543 15.20×38.10 8
15×45 1772×4488 15.20×45.70 9
18×24 1772×5315 17.80×24.00 10
18×25 2126×2835 17.80×25.40 11
20×25 2126×2953 20.30×25.40 12
20×30 2362×3543 20.30×30.50 13
25×38 2953×4488 25.40×38.10 14
30×40 3543×4724 30.50×40.60 15
30×45 3543×5315 30.50×45.70 16
30×90 3534×10630 30.50×91.40 17

To find out which inch photo sizes correspond to standard parameters, you just need to convert centimeters to inches by dividing them by 2.54 or use a special table.

Correspondence table for standard photo sizes in inches and pixels:

Standard Size (pixels) Size (inches)
9×13 1063×1535 3.5430×5.1170
10×15 1181×1772 3.9370×5.9070
13×18 1535×2126 5.1170×7.0870
15×20 1772×2362 5.9070×7.8730
15×21 1772×2362 5.9070×8.2670
15×22 1772×2480 5.9070×8.6600
15×30 1772×2598 5.9070×11.8100
15×38 1772×3543 5.9070×14.9600
15×45 1772×4488 5.9070×17.7170
18×24 1772×5315 7.0870×9.4500
18×25 2126×2835 7.0870×9.8430
20×25 2126×2953 7.0870×9.8430
20×30 2362×3543 7.8730×11.8100
25×38 2953×4488 9.8430×14.9600
30×40 3543×4724 11.8100×15.7470
30×45 3543×5315 11.8100×17.7170
30×90 3534×10630 11.8100×35.4330