GNU bug report logs - #74476
[PATCH] Explore JPEG loading without quantization

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From: Manuel Giraud <manuel <at> ledu-giraud.fr>
To: Alan Third <alan <at> idiocy.org>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 74476 <at> debbugs.gnu.org
Subject: bug#74476: [PATCH] Explore JPEG loading without quantization
Date: Sun, 01 Dec 2024 12:13:53 +0100

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Alan Third <alan <at> idiocy.org> writes:

> On Sat, Nov 30, 2024 at 07:32:10PM +0100, Manuel Giraud wrote:
>> Alan Third <alan <at> idiocy.org> writes:
>> 
>> > Probably I could do with finding some larger images as the whole thing
>> > completes in under a second even without your patch.
>> 
>> FYI, I have used images of 4000 by 3000 pixels.
>> 
>> > I've had a quick dig into lookup_rgb_color and assuming you have a
>> > true colour display and there's no gamma calculation going on (I don't
>> > know when that happens) it shouldn't be doing a whole lot more.
>> > Perhaps it's just the extra over-head of calling a function?
>> 
>> It seems a bit much for just a function call.  Or maybe it is the
>> init_color_table call?  Should it be done for each jpeg_load?
>
> It's 4000x3000 function calls, so it might have an effect...

Yes, you're right.  I missed this 😅.

> I think it should be done for each load. And I just noticed you need
> to add a free_color_table call after you're done with it.

Yes, I have re-add it in the attached new version of the patch.  I also
re-add the ir, ig and ib indices computation.  WDYT?

> I get that it's a waste of time allocating the table on a true colour
> display because it's never going to be used, but it seems to make no
> performance difference here and it is still needed on other display
> types.

Ok, I thought about making this allocation conditional to having a true
color display or not... but if you say that there is no performance
gain, it might not worth it.

> Purely for testing purposes I tried changing the PUT_PIXEL call to
> this:
>
>     PUT_PIXEL (ximg, x, y, x_make_truecolor_pixel (FRAME_DISPLAY_INFO(f), r, g, b));
>
> I think it might have given an improvement, but it was so slight I
> can't say for sure. That obviously can't be used outside of testing,
> but it lets us rule out the function call, etc.

Yes and the gamma correction part is also missing.

[0001-Do-not-use-libjpeg-quantization-bug-74476.patch (text/x-patch, attachment)]

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-- 
Manuel Giraud

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