I have hard time finding ISkpRenderer counterpart in C SDK.
How can I get raw image SketchUp output in C SDK?
I am interested in doing it “live” in SU, not in an external app.
(Before the OP was edited to indicate working on “live” model …)
Didn’t they implemented a C parity for the Ruby API’s ImageRep class ?
Hold on, … Looking in the docs …
Yea, here it is …
https://extensions.sketchup.com/developers/sketchup_c_api/sketchup/image__rep_8h.html
There is SUImageRep, but I have impression it is for reading textures only.
I want to get SketchUp view output as raw bytes.
I will check it too.
Oh you actually meant an equivalent of View#write_image ?
There has historically not been any rendered view object in the standalone C API as it is currently only for working on files. But this will or should change when working on a “live” model within the SketchUp application.
Is this what you are doing ?
Yes. In C++ there was ISkpRenderer->RenderToBitmap()
It was giving an unsigned char array of an active view at a requested resolution, dpi and few other parameters specified.
It is a pity. I will have to save the output to a file to read it back. 
Yes, (material and image object textures) but I think it has been requested to use it for other things.
It does seem useful that both APIs could benefit from a view#image_rep or scene_page#image_rep (or maybe a camera#image_rep would handle both as they both have a camera object.)
I looked through the API Feature Requests but could not find it logged. Could you open an issue for this please?
FYI: There is a request to get ImageRep objects of SKP file thumbnails …
Added