Expose underlying error message when attempting to read metadata from "corrupt" file

[HRK44]

Is it possible to get a JPG image's process ? (SOF type etc...)

[lovell]

Hello, not sure I quite understand this question but did you see metadata? This includes an isProgressive flag, which is perhaps what you meant.

[HRK44]

@lovell On site like get-metadata dot com, I can have a field called Encoding Process which on my JPEG images is Encoding Process: Lossless, Huffman coding or in some others ones Encoding Process: Baseline DCT, Huffman coding. So my question is can I get this kind of data using sharp?

I tried to use the metadata but it can retrieve only the width/height, I don't see other information in it.

[lovell]

Thanks for clarifying. Lossless JPEG images are unlikely to work as the underlying libjpeg(-turbo) does not support them. Beyond that, I think the only two "encoding processes" are "baseline" (where isProgressive is false) or "progressive" (where isProgressive is true).

[HRK44]

@lovell I understand that it cannot decode JPEG Lossless, but I thought it could at least read the metadata since it's still official JPEG format. Even when I use identify command in Linux, the error message is identify-im6.q16: Unsupported JPEG process: SOF type 0xc3 `0' @ error/jpeg.c/JPEGErrorHandler/322. which explicitly says that the file is a SOF3 (0xc3), which is the kind of data I need lol

[lovell]

Are you able to provide a sample lossless JPEG file? If so, I might be able to take a closer look at how libvips could be updated to expose this.

[HRK44]

@lovell I'll try to provide one ASAP, thanks for looking into this

[HRK44]

@lovell How can I contact you and send you privately one image?

[lovell]

I found a public testimgl.jpg example in ftp://ftp.fu-berlin.de/unix/X11/graphics/ImageMagick/delegates/ljpeg-6b.tar.gz

I can see the "Unsupported JPEG process: SOF type 0xc3" error message is being passed back from libvips but is swallowed by sharp.

[lovell]

v0.21.2 now available that exposes the underlying error message, if any.