On 8/11/17 11:13 am, Mark Waddingham via use-livecode wrote:
On 2017-08-11 09:29, Richmond Mathewson via use-livecode wrote:
In theory that sounds both impressive and useful . . .
But, what, apart from your stack can read the format/compression
method properly.
I think Hermann's suggestion is a bespoke way of reducing resource
size for built apps and their content - as there isn't a 'standard'
for JPNG (yet) it isn't really useful for interchange between apps,
but it might be that a standard does appear at some point.
Can your stack export a JPNG image?
It doesn't need to in order to be useful. This is something which
could be used at the point of building a standalone (in a
standaloneSaving handler, for example) to convert PNG images into a
smaller form for use by the app at runtime.
It may not, but the stack does export images with a .lcjpng suffix . . .
and the question is what for?
Richmond.
"This may even result in a larger data size than the original when
decompressing."
I'm not sure I quite understand that comment...
Any (loss-less) compression algorithm will produce output which is
larger than the input for some inputs
(https://en.wikipedia.org/wiki/Lossless_compression#Limitations). So
all (such) compression algorithms tend to have a flag in their encoded
output which says 'this is not compressed'. When the compressor runs,
if the output is greater in size than the original input it just emits
the output with that flag and the original data. (In this case, if the
JPNG process produces a data size larger than the original PNG, just
use the original PNG!).
In this case the JPNG idea exploits the fact that color images tend to
withstand data-loss, but alpha data (masks) do not - JPEG is lossy, it
removes information which our eyes cannot see. PNG compression (a
variant of gzip IIRC) is loss-less, it preserves the exact values of
the inputs. So you use the lossy method (JPEG) on the part of the
image which makes no difference to our eyes, and the loss-less method
(PNG) on the part of the image which our eyes would notice a
difference in.
Warmest Regards,
Mark.
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