Hello, I would like to obtain DCT coefficients of a jpeg image. The Phil Sallee’s JPEG toolbox in MATLAB returns these as an array (the original website is not active, but some of the code can be downloaded on Jessica Fridrich’s website under the DOWNLOAD heading) How can I obtain the coefficient…

[image] pakk-minidose: The Phil Sallee’s JPEG toolbox in MATLAB returns these as an array (the original website is not active, but some of the code can be downloaded on Jessica Fridrich’s website under the DOWNLOAD heading) I took a crack at translating this code into Julia using the JpegTur…

Glancing at Sallee’s source code, it seems to be a very thin Matlab MEX wrapper around libjpeg , which is a popular C library to access JPEG files. It should be pretty easy to write a Julia package to call libjpeg, or even just a few lines to extract the information you specifically want. We alread…

[image] stevengj: It should be pretty easy to write a Julia package to call libjpeg I took a look at this, and it’s not such a simple task for beginners because of the complexity of the libjpeg API. However, I put together a start at: [image] GitHub - stevengj/JpegTurbo.jl: Julia …

Indeed. It’d be great to make a JPEGFiles.jl for inclusion in ImageIO.jl . I won’t be able to push that forward, but very happy to review. As well as the ImageIODevelopment.jl repo, I’d recommend looking at PNGFiles.jl which is a pretty finished product thanks in large part to @drvi

Incidentally, about 5 years ago, I wrote a JPEG (baseline) decoder as an exercise in learning Julia. The original code doesn’t work with Julia v1 and the latest packages, so I’m trying to modernize it little by little, but I’ve been too busy lately. :sob: [image] GitHub - kimikage/LowLevel…

Thank you everybody for your great replies! However, when trying out @stevengj 's code, I run into the following error: JPEG parameter struct mismatch: library thinks size is 600, caller expects 632 The test code was run using Julia 1.6.2 and the code was following: using Pkg; Pkg.activate(temp=…

[image] pakk-minidose: JPEG parameter struct mismatch: library thinks size is 600, caller expects 632 Probably some of the libjpeg types are different under Windows (your machine) vs Mac (my machine). Can you run using Clang, JpegTurbo_jll jconfig_h = joinpath(JpegTurbo_jll.artifa…

Here is the diff. I below is a screenshot of the output as it is easier to read with its color coding PS C:\tmp> git diff --no-index .\libjpeg_common_win.jl .\libjpeg_common_mac.jl warning: LF will be replaced by CRLF in .\libjpeg_common_win.jl. The file will have its original line endings in your …

[image] pakk-minidose: Here is the diff. I below is a screenshot of the output as it is easier to read with its color coding It looks like the culprit is the boolean type, which is apparently unsigned char on Windows and int on Mac. I’ve pushed an update that should fix this.

Great! It now works on Windows. I’ve done a very coarse comparison with the MATLAB output and it seems to do the same. Thank you for your help!

Just adding a small bugfix. It seems that the Julia Libc FILE does not release the file descriptor even though it is not reachable anymore, see this comment in the source code . I found out when my Julia instance ran out of file descriptors (Linux limits number of file descriptors per process to 102…

Get DCT coefficients of jpeg image

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Get DCT coefficients of jpeg image

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