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Free Lossless Image Format
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native jpg decoding #144

Open matthiaskrgr opened 8 years ago

matthiaskrgr commented 8 years ago

It might be nice to have jpg reading support. Currently flif does not accept jpgs.

While converting jpg to flif is obviously not something desirable since jpg already implies loss of information in most cases, having to convert jpg to png and then png to flif (if there are no losseless originals of the jpgs available) is not very comfortable either...

jonsneyers commented 8 years ago

Could be nice in combination with storing the actual pixel data in YCbCr, like JPEG, instead of the reversible YCoCg we're using by default. We could use this: https://cdn.rawgit.com/libjpeg-turbo/libjpeg-turbo/1.4.x/doc/html/group___turbo_j_p_e_g.html#ga0828a38ae29631ac28b6857cefb0eebf

psykauze commented 8 years ago

I've made some benchmarks with jpeg files as inputs just for fun.

As expected, conversion from lossy to lossless format is non-efficient here a screenshot of the results. (Sorted by "FLIF non-interlaced"/"JPEGtran progressive" ratio)

lossyjpgvsflif

jonsneyers commented 8 years ago

Interesting. What quality are those JPEG originals? I would expect the ratio to be different depending on the JPEG quality. Obviously encoding compression artifacts has a cost, while it is "free" for the format that produces the artifacts :).

Also, it would be interesting to see a comparison between partial FLIF files and JPEG files w.r.t. some perceptual metrics like SSIM. I.e. take a lossless original, compress it with FLIF, compress it with JPEG at various quality settings, decode truncated versions of the FLIF file, and plot the results (bits per pixel on the x-axis, SSIM on the y-axis or something like that).

psykauze commented 8 years ago

I'm using various images (300) I've got from a homemade sharing files website. There's drawings, pictures, screenshots, fractals, memes, scans, etc...

I'll sort images by bit-per-pixel. sort-by-bpp

I also attach the log file: jpeg2flif.txt

jonsneyers commented 8 years ago

uncmpJPG can be used to extract the raw DCT coefficients (I think those are 12 bit signed ints or something like that) from a JPEG file: https://github.com/packjpg/JPEG-Developers-Package/tree/master/uncmpJPG

We could use FLIF to store the raw DCT coefficients. Maybe store it internally as an animation with 64 frames (one for each DCT coefficient), or something like that.