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Why does the file size increase when I resample to a lower resolution?
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?
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
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.