Image resolution and size in Photoshop

Display the current image size

To view the current size of your image, go to List Image in the menu bar and select Image size :

This opens Image Size dialog box In Photoshop with a preview window on the left and image size options along the right. The preview window is only available in Photoshop CC :

The current size of the image, in pixels and megabytes, is found at the top. next to the words Image size -See that my picture running Currently 69.1 million (MB) in memory. And next to the word الأبعاد , it shows that my picture has عرض of 6016 pixels و Height of 4016 pixels :

current precision value

If you look down, you will find an option Precision . For my image, the resolution is currently set to 300 pixels per inch . You may be set to a different value, and that's okay:

What is the resolution of the image?

So what she Exact image resolution, and what does this option in the Image Size dialog actually do? There is a lot of confusion regarding the value of resolution, especially when it comes to uploading images to the web. So let's start by learning what image resolution really means.

Picture Resolution do one thing and one thing only; It controls the size of that your image will printed . The Resolution value in the Image Size dialog box in Photoshop determines how many pixels of your image will be printed per pixel Linear inches of paper . Packs higher resolution values a greater number of Pixels are in linear inches, which results in a print size smaller . And it packs lower resolution values fewer than Pixels per inch, which gives us a print size Larger .

How does image resolution affect print size

For example, a resolution of 300 pixels per inch means that 300 pixels of the image's width will be packed into every inch of the paper from left to right. This also means that 300 pixels of the image's height will be packed into each inch of the paper from top to bottom.

To find out the actual print size, we just divide the image's width and height, in pixels, by the resolution value. So, with my photo, show 6016 pixels , divided by the precision value 300 pixels / inch , means that my image will be printed wide 20.053 inches almost . And we can do the same thing with altitude. to rise 4016 pixels Divided by 300 pixels / inch Means the height of my image when printing will be 13.387 inches almost .

Displays the current print size

Directly above the resolution value in the Image Size dialog box is Display و Length options. To view the current print size of your image, change the measurement type Width and height in pixels to inches . And here we see that sure enough, at a resolution of 300 pixels/inch, my image would print 20.053 inches wide by 13.387 inches tall. And that's all Image Resolution does. It controls what size your image will print, and nothing else:

Why does image resolution not affect file size?

Now that we know that the image resolution controls the print size of the image, let's look at why the resolution value has no effect on the image file size your picture .

Many people think that before you email or upload an image to the web, you need to lower its resolution, usually to around 72 pixels/inch. The idea is that by lowering the resolution, you reduce the file size, allowing the image to download faster. And yes, smaller file sizes are doing Download faster. But lowering the resolution did be Make file size smaller.

The reason is, the image file size depends entirely on pixel dimensions . That is, the number of pixels in width and the number of pixels in height. Changing the print resolution does not change the number of pixels, and therefore does not affect the file size. We can easily demonstrate this in Photoshop's Image Size dialog.

Resample option

First, we need to make sure we're changing the resolution فقط Not the number of pixels. And we do that by making sure turning off Run an option Re-existing sample Just below the resolution value (not specified). Means Reshape We change the number of pixels. And if we change the resolution while running a Resample, the pixel dimensions will change with it. In this case, we only want to change the precision value, so make sure Resample is turned off:

Current image size, pixel dimensions, and resolution

Note that at 300 pixels/inch, my image's file size is currently 69.1 MB . It has a width 6016 pixels and its height 4016 pixels . I show you exactly how image size and pixel dimensions relate in my tutorial How to calculate image size :

Decrease the accuracy value

I will lower the resolution from 300 pixels/inch to the common "web resolution" of 72 pixels / inch :

But although the resolution value has decreased, the pixel dimensions have not changed. still Image show 6016 pixels and length 4016 pixels . And because the pixel dimensions haven't changed, the file size hasn't changed either. Still exactly as it was before 69.1 million :

In fact, the only thing that I did The change was in print size From the picture. By lowering the resolution to just 72 pixels/inch, the width of the image, when printed, increased from 20 inches to more than 83 inches . The print height has also increased, from 13 inches to approx 56 inches . But, even though the print size has changed dramatically, the file size hasn't changed at all, so the image won't download any faster if you want to upload it to the web:

You can learn more about where the idea for "web resolution" came from in my article on Web resolution legend 72ppi .

Increase the resolution value

Let's see what happens if we do the opposite By increasing Precision. I'm going to up it from 72 pixels/inch to something crazy, like 3000 pixels / inch , which is more than anything you could possibly need. I show you exactly how much resolution you need for high quality prints in Pictures resized for a lesson techniques In this series:

Again, we see that although the resolution has changed, the pixel dimensions have not. And because the pixel dimensions are the same, the file size remains the same:

As expected, the only thing that did not Print size has changed. At a resolution of 3000 pixels/inch, the image will now print in width 2.005 inches and length 1.339 inches Just . But it won't look any different on your screen, nor will it download any faster or slower:

if I were not Need to change the image file size, you will need to change the number of pixels. I show you exactly how to do that in my photo resizing for email and photo sharing tutorial.