Re: JPEG compression in a TIFF file, pointless?


"cypherswipe" <cypherswipe@xxxxxxxxx> wrote in message
news:1135296106.755237.206660@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>>You're comparing apples to oranges. JPEG is not a file format, it is a
> codestream format. One popular file format for JPEG is JFIF
>
> I know that, it's just a question of semantics. I know that what
> everyone knows as a "JPEG" image is actually a JFIF.

or Exif, or JFXX or just raw codestream.

> I should have made
> a point of being more accurate in my wording.
>
> I'm comparing an image saved as a standard (JFIF) JPEG, and the exact
> same image saved as a TIFF using JPEG compression. At the same visual
> quality level, the TIFF is still HUGE compared to the JPEG/JFIF.

That seems wrong somehow. I'm not an expert in TIFF, but I wouldn't have
thought that it would be much larger than the corresponding JFIF.
Perhaps the JPEG encoder in the TIFF generator has a different
understanding of the quality factor than the encoder for JFIFs.

> The
> TIFF is anywhere from 3 to 5 times as large as the JPEG/JFIF. So the
> question remains, is there ever any reason to use JPEG compression in a
> TIFF file? A JFIF/JPEG gets much better filesize for the same visual
> quality, and a TIFF compressed with LZW, ZIP, or packbits is only
> slightly larger than one that's JPEG compressed, but doesn't throw away
> any image data.

I think this is probably only the case for very simple images (or a JPEG
matrix of all 1s). Use a hex editor to look at the DQTs in the TIFF and
the JFIF, and see how they compare.


.

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