JPNG

Mark Waddingham mark at livecode.com
Fri Aug 11 04:13:25 EDT 2017


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.

> "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.

-- 
Mark Waddingham ~ mark at livecode.com ~ http://www.livecode.com/
LiveCode: Everyone can create apps




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