How to Resize and Compress Images

How to use simple tools to resize or compress your images to target dimensions and file size. Also learn the principles that affect image file sizes and effective compression.

Suggested image targets

The following recommendations may change, but this is how they are now.

  • iTunes show- and episode-level cover art (RSS feed): square between 1,400 × 1,400 and 3,000 × 3,000. Must be smaller than 512 KB.
  • Embedded episode-level cover art (ID3 tags): square ideally between 1,400 × 1,400 and 3,000 × 3,000, but more important for it to be smaller than 220 KB.

Warning

These principles will only help you decrease the quality or size of an image. Using these principles in attempts to increase your image quality usually won't give good results.

If you must increase the quality or size of an image, it’s best to go back to a higher-quality or vector master file, or remake the image with higher-quality assets and at higher dimensions.

Fast and simple tools

Use iLoveIMG for simple tools to compress, resize, crop, or convert.

Use Optimizilla for a little more control over compression and quality.

Compression principles

Image file size is affected by four different factors:

  • Format—JPEG is best for photographs or images with a lot of texture, PNG is best for images with large portions of solid colors (not gradients)
  • Dimensions—The more pixels there are in a file, the larger the file will be. Thus, a 600 × 600 image will be smaller than a 1,400 × 1,400 image.
  • Compression—Many image formats can compress that data for smaller file sizes. Some formats, such as TIFF, can do this without losing image quality (called “lossless compression). Other formats, such as JPEG, reduce the image quality as you increase the compression (called “lossy compression”). And formats like GIF or PNG compress by reducing the number of colors the image can use, which is a form of lossy compression.
  • Detail—Textures and patterns take more space than solids because of the amount of detail.
  • Metadata—Information attached to each file that doesn’t change the image itself, but does describe aspects of the image, such as location, color profile, camera information, and such. It’s like ID3 tags for MP3 files, but image metadata is usually not necessary for Internet images.