How to compress an image in Adobe Photoshop

Adobe Photoshop is a versatile and highly-capable graphics editing program.  In addition to all of the graphical features it has, it also allows for a wide range of compression options when saving a file.

There are various reasons for using file compression, and how tightly you want to compress an image depends on what you are going to use it for.  Compression reduces an image's file size, which can help it to load faster on a web page, transmit faster in an email, or download faster to someone's computer.

Using Photoshop, you can easily compress your images to whatever size you need.  This article describes the process for compressing an image in Photshop.  (These instructions were written using Photoshop Elements 7, but the compression options for other versions of Photoshop will be similar, if not identical.)

Open Photoshop and load the image that you want to compress.  Click File on the menu bar and choose "Save for Web."  Two versions of your image will appear on the screen; the original will be on the left and the compressed version will be on the right, so as you change compression options you can see how it affects the image quality.

You have a lot of control when it comes to compressing an image in Photoshop.  On the right side of the window are all of your compression options.  First you can choose the file type that you want to save your image as, which will give you a baseline compression.  (For example, JPEG images are compressed more than GIF images.)

Once you've settled on a file type (which will typically be JPEG, GIF, or PNG) you can choose to compress your image by quality or by pixel size, or both.  By changing the number in the Quality field, you will reduce the quality of your image as well as reduce its file size.  You can choose a quality setting by number (0-100) by using the sliding scale or by typing in a number, or you can use the preset quality settings to the left -- Low, Medium, High, Very High, or Maximum.  Selecting one of these settings will fill in the corresponding quality number.  For example, selecting High will set the quality to 60.

You can also choose to compress the image by reducing its pixel count.  Under the Image Size header below where the quality settings are, you can see your image's current pixel count.  Beneath that, you can alter the pixel count by either typing in a new pixel count that's lower than the current count, or by using a percentage (from 0.01% to 512%).  If you check the "Constrain Proportions" box, the image will retain its current dimensions, no matter how small you make it.  Once you've found a pixel count or percentage you like, click Apply to see how it will affect the image quality as well as the file size.

At the bottom of the screen, under the view of the right-hand image, you'll see how much disk space your file will take up using the current compression settings.  You can play around with the numbers to see how they affect file size, as well as estimated download speeds which are also displayed below the file size.

Once you've found the compression level that you're satisfied with, click OK at the top of the screen to save the file.  Keep in mind that this image will be saved with the new compression settings, so it's a good idea to keep a copy of the original image in case you need a less-compressed version of it later.

(Originally published on Helium.com, January 2011)