I've got comics in CBZ format with pictures in 2k or 4k pixels tall and when I try converting them to EPUB, Calibre shrinks the pictures to 1k or under, making them very blurry to view on a mobile or tablet. Is there a setting or type of script I can use to convert each picture to its own EPUB page and not have Calibre shrink the picture?
When you open the conversion window, before actually starting the process, go to the
comic input tab, you will find a box labeled
change images dimensions1.
By default, Calibre uses the settings from the
page setup tab to select standard output settings for the selected device, this includes that device screen size, to which the images are resized.
By putting a custom value (in your case, the original dimensions of the pictures inside the CBZ files) on the
change images dimensions box, you can force Calibre to use these values instead of the preset ones from the
page setup tab.
1 - Or something similar: I'm using the italian version, the actual wording may be a little different.
Try Kindle Comic Converter. Despite its name, it works for all types of readers, and can output EPUB. Be sure to select the generic reader output, enable Color Mode, and select EPUB as the output format.