Usage question -- Getting access to the in-memory representation of the compressed data

[hmaarrfk]

Happy new year!

Thank you for the great work! I've been testing this library and I find it quite compelling.

I actually managed to write some python wrappers to help me better benchmark things when compared to other compression options.

I was wondering if there was a way to get access to the "binary data" that we must dump to a tiff in order to make this "compliant" with OpenJPEG'ed compressed TIFF page.

I know you are working with openjpeg to do this uclouvain/openjpeg#1487

however, while waiting, is there a way to access the "compressed data" and the "required headers" as data pointers for us to write to a file (or memory bufffer) ourselves?

I hope this question makes sense.

Best,

Mark

[hmaarrfk]

For example, for the "decompression path" i found the line interface of codestream.pull

https://github.com/ramonaoptics/ojph/blob/main/ojph/_imread.py#L96

[aous72]

Hi Mark,

Happy holiday season!
Glad you found the library useful.

I am a bit confused about the question.
I think you are asking if you can compress an image into a memory file.
The answer is yes. You can use ojph::mem_outfile

OpenJPH/src/core/common/ojph_file.h

Line 126 in 1b20dbc

class OJPH_EXPORT mem_outfile : public outfile_base

Then you use the created object as an output file for compression, using it in codestream.write_headers().
Then you can access the compressed data from this memory file, copy it somewhere else, or write it to a file.

Alternatively, you can use develop a derived class/object from ojph::outfile_base, and use it, where ojph::mem_outfile serves as an example implementation, as Chris Hafey is doing in https://github.com/chafey/openjphjs/blob/master/src/EncodedBuffer.hpp

Does that answer the question? please let me know.

[hmaarrfk]

I think this answers my question. I'll have to study it in a bit more depth. I had a hunch that this is what I was supposed to look for but I wasn't sure.

As a followup question. do you know if this is "in memory file" is what I need to dump to a TIFF page in order for readers to open it correctly?

Do you know of a TIFF reader that can open OpenJPEG files that I could test my writer against?

[aous72]

I am not familiar with TIFF pages, and TIFF in general.
I am sorry I cannot help in this regard.

[hmaarrfk]

Alright, thank you so much already, i'll close this and maybe reopen or get in touch again if I have new questions.

Happy new year!!!