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radius · 01-21-2019, 11:32 AM

Not best practices, but this is what I do for my personal reading enjoyment:

- if I can get away with it, I turn the picture into straight, 1-bit, black and white. This works fairly well for scans of illustrations from pulp magazines and paperbacks. Doing it this way does risk losing some detail and it can be difficult to find the right cutoff level. However, I think it looks the best on an actual e-ink display.

Even 12 inch tablets top out around the 1200x1600 mark right now so I scale the image to fit within that before messing with the colour.

I save these as 1-bit gif or png depending on what my fingers feel like typing on that day.

- if the original illustration was in colour, or in delicate gray scale, then I try to boost contrast and then do a dithered conversion to 4-bit gray scale. This requires some trial and error because it won't look good on a computer monitor.

I do the conversion to gray scale because I believe that computer-based graphics programs can do a better job with the re-scale and colour conversion than an eink reader can do on the fly, since the reader will have to be optimised also for speed of display.

I save these are png if there aren't too many illustrations and/or they aren't too big. If I am having trouble with the size of the epub, then I might choose jpg, but then I don't bother with quantizing to only 16 grey levels and only do the contrast boost.

An example of this kind of image might be some of the Ruritanian trilogy ones.

- if I am making an "archival" book, then I just save the largest and best quality image file that I can get.

I'll try to add some example images to this post when I get home.

01-21-2019, 11:32 AM	#32
radius Lector minore Posts: 652 Karma: 1738720 Join Date: Jan 2008 Device: Aura One, Paperwhite Signature	Not best practices, but this is what I do for my personal reading enjoyment: - if I can get away with it, I turn the picture into straight, 1-bit, black and white. This works fairly well for scans of illustrations from pulp magazines and paperbacks. Doing it this way does risk losing some detail and it can be difficult to find the right cutoff level. However, I think it looks the best on an actual e-ink display. Even 12 inch tablets top out around the 1200x1600 mark right now so I scale the image to fit within that before messing with the colour. I save these as 1-bit gif or png depending on what my fingers feel like typing on that day. - if the original illustration was in colour, or in delicate gray scale, then I try to boost contrast and then do a dithered conversion to 4-bit gray scale. This requires some trial and error because it won't look good on a computer monitor. I do the conversion to gray scale because I believe that computer-based graphics programs can do a better job with the re-scale and colour conversion than an eink reader can do on the fly, since the reader will have to be optimised also for speed of display. I save these are png if there aren't too many illustrations and/or they aren't too big. If I am having trouble with the size of the epub, then I might choose jpg, but then I don't bother with quantizing to only 16 grey levels and only do the contrast boost. An example of this kind of image might be some of the Ruritanian trilogy ones. - if I am making an "archival" book, then I just save the largest and best quality image file that I can get. I'll try to add some example images to this post when I get home.