Quote:
Originally Posted by derangedhermit
1. I do not know why the 256-color indexed pngs are 60%-65% of the size of the 256-shade grayscale pngs. That seems like something isn't equal, and I want to know the explanation. I prefer to use a grayscale format for grayscale images.
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Quote:
Originally Posted by DaleDe
In answer to 1. Indexed formats are always more efficient that regular formats. This is why GIF is always indexed. With an index the color is only defined once and then referenced multiple times.
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More efficient when dealing with few colors*. In this case, YES, PNG will destroy a format that tries to keep all the colors under the sun. (Because it can toss out all the useless information and only deal with <256 colors.. this dramatically cuts down on filesize).
As to the grayscale question... I am also not TOO sure on the technical specifics, but the larger filesize, it could be two things that I can think of:
1. Grayscale IS a different beast from Indexed, perhaps it is stored in a way that does not compress as efficiently.
http://www.libpng.org/pub/png/book/c...g.ch08.div.5.3
When saved as "Grayscale", the image is stored using luminance (Y) instead of an Indexed table of colors.
2. Perhaps the program used to create the images uses different libraries/code to compress both of these types.
This is part of the reason why most of us typically run PNGs through other, more powerful, optimization programs (optipng, pngcrush, scriptpng, ...). Many of these image programs when saving PNGs, will also save it with A LOT of extra bloat (which is partly why you always want to save with something along the lines of the "Save Image for Web").
Quote:
Originally Posted by DaleDe
Some sort of crunching would seem in order. PNG seems not to compress itself very well.
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Oh, PNG compresses VERY well.
Just that it is
LOSSLESS. JPG can seem much smaller for "photographic" images, because it gets to toss out lots of information (least significant bits) that "the human eye can't see".
Quote:
Originally Posted by derangedhermit
On the bright nighttime thing, I would see if I could add partial transparency and what that looked like. That might be nice when people pick textured or tinted backgrounds in general (or not ). |
Transparency... now that is a problem on the ereaders. Perhaps the next generation of ebooks will be able to handle it better.
See the serious bug I ran into in my Formula Tutorial topic here:
https://www.mobileread.com/forums/sho...5&postcount=12
I would recommend steering clear of transparency for now (although it would be GREAT, since you wouldn't have a glaring white background).