Comment 16 for bug 521323

then there are people such as me who had to replace my scanner's glass - I guess the glass from the hardware store is more green / uncoated than the original - so it needs some adjustment in all cases; in the color case usually brightness/contrast adjustments are sufficient to make it look reasonably normal - although realistic-looking photos are a different matter!

in the monochrome case, similarly a greyscale scan then brightness/contrast adjustments are necessary, it would be nice to have preset adjustments available so that the scan as directly saved from simple scan was already reasonably adjusted;

so I'd suggest, for the monochrome case, a brightness/contrast[/gamma?] setting to 'prefilter' the 1bpp type result [currently 'text' setting], so that for all possible scanners it could produce a legible document, possibly in addition to the 2bpp 4-value type result you are mooting?

It would seem that this links to #498029 although I'd reiterate what has already been said, that it would be nicer to filter the image before saving [even before preview really], rather than adding a color profile to the saved image - particularly as a quick look at the patch there seems to suggest that for instance pdf images can't have embedded color profiles

as there is the possibility of calling imagemagick [when installed] from the code, it would seem reasonably straightforward to call it to prefilter images; then the monochrome scan could simply be an 8bpp greyscale scan, that is subsequently filtered into a 1bpp / 2bpp 'preview' image for saving/sending/etc

could possibly add imagemagick/graphicsmagick libs to the deps then call the lib functions directly from the code