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Solution TitleWhy does the file size increase when I resample to a lower resolution?
Solution Number00000793
Solution Details
Symptoms
I have an Action List to resample images at a lower resolution in order to reduce file size but the file size is actually increasing, why is this?

Cause
It may be that the file contains indexed color.  Each pixel in an indexed color image is a single number in a table of colours. For non-indexed images you need at least one number for each channel. For RGB that means 3 numbers per pixel, as opposed to the 1 number for an indexed image. As you can imagine, this results in much smaller file sizes.

When resampling we can't keep the indexed colour space because the colour of a result pixel has to be a combination of several original pixels. That resulting colour may not be in the original table of colours. Therefore the image is de-indexed before resampling. So while you're reducing the amount of pixels you're increasing the amount of numbers (bytes) needed to represent each pixel. The result is an increase in file size.

Solution
You can re-index the image after resampling with the action "Convert images to indexed color space" and get the reduced file size you desire.
 
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