Image rescaling

Image rescaling

[Lars Magne Ingebrigtsen]

Most of the image format decoders (jpeg and gif, for instance) do not
support image rescaling.  So shr uses ImageMagick for all its image
handling.

There are two problems with this:

1) ImageMagick is crashy.  Virtually all Emacs crashes I get happen deep
in the ImageMagic code.  I mean, I don't get a lot of crashes, but they
happen from time to time, and are pretty annoying.

2) Some people run Emacs without ImageMagick built in, but usually have
the other libraries enabled.

So I would propose to add a general image scaling function, and use that
in all the image handling functions.  Without image rescaling, Emacs is
pretty useless for anything that involves handling images.

Does this sound OK to everybody?

And if so, is there an FSF-copyright-assigned quality image rescaling
function out there that I could adapt to Emacs so that I don't have to
write it myself?  >"?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Re: Image rescaling

[joakim]

Lars Magne Ingebrigtsen <larsi@gnus.org> writes:

> Most of the image format decoders (jpeg and gif, for instance) do not
> support image rescaling.  So shr uses ImageMagick for all its image
> handling.
>
> There are two problems with this:
>
> 1) ImageMagick is crashy.  Virtually all Emacs crashes I get happen deep
> in the ImageMagic code.  I mean, I don't get a lot of crashes, but they
> happen from time to time, and are pretty annoying.
>
> 2) Some people run Emacs without ImageMagick built in, but usually have
> the other libraries enabled.
>
> So I would propose to add a general image scaling function, and use that
> in all the image handling functions.  Without image rescaling, Emacs is
> pretty useless for anything that involves handling images.
>
> Does this sound OK to everybody?
>
> And if so, is there an FSF-copyright-assigned quality image rescaling
> function out there that I could adapt to Emacs so that I don't have to
> write it myself?  >"?

Its a pity ImageMagic is crashy, but I take your word for it, since i
dont experience it myself.

Maybe something can be extracted from Gimp or Inkscape?
Other than that, implementing a schoolbook image rescaling algorithm
shouldnt be too much work.

-- 
Joakim Verona

Re: Image rescaling

[Lars Magne Ingebrigtsen]

joakim@verona.se writes:

> Other than that, implementing a schoolbook image rescaling algorithm
> shouldnt be too much work.

Rescaling is apparently a pretty tricky thing that is mostly implemented
wrong:

http://www.4p8.com/eric.brasseur/gamma.html

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Re: Image rescaling

[Stefan Monnier]

> Rescaling is apparently a pretty tricky thing that is mostly implemented
> wrong:

> http://www.4p8.com/eric.brasseur/gamma.html

Rescaling an image is exactly the same problem as resampling an audio
file (e.g. to play it at 48KHz instead of the 44.1KHz used on the CD
from which it came).

Doing it naively works, but in some cases gives very poor
results, indeed.


        Stefan

Re: Image rescaling

[David Kastrup]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> Rescaling is apparently a pretty tricky thing that is mostly implemented
>> wrong:
>
>> http://www.4p8.com/eric.brasseur/gamma.html
>
> Rescaling an image is exactly the same problem as resampling an audio
> file (e.g. to play it at 48KHz instead of the 44.1KHz used on the CD
> from which it came).
>
> Doing it naively works, but in some cases gives very poor
> results, indeed.

Nice meditation but not related to the referenced article.  The article
is concerned about non-linear quantization.  That's "exactly the same
problem" as using a good 48kHz to 44.1kHz resampling algorithm on
uLaw-quantized audio data rather than linearly-quantized data.

Entirely different problem to mess up on.

-- 
David Kastrup

RE: Image rescaling

[Mirek Kaim]

> From: larsi@gnus.org
>
> Mirek Kaim <mirek.kaim@outlook.com> writes:
>
>> convert to hsl, rescale using bilinear (should be fine for a start),
>> convert back to rgb? that should do the trick i guess. and it should
>> be pretty fast and easy to implement. unic0rn
>
> Yeah, looks pretty easy. When rescaling to a smaller size, some kind of
> blurring (Gaussian seems popular) has to be done first, apparently.

that wouldn't be bilinear anymore i guess. sure, gaussian or lanczos
could be implemented, but for a fast start bilinear or perhaps bicubic
should be sufficient. doing it in hsl colorspace should prevent artifacts,
and the whole thing will be pretty small and easy to code.

unic0rn

ps. i hope my email won't end up in one line this time,
no idea what the hell happened last time :/

 		 	   		  

Re: Image rescaling

[joakim]

joakim@verona.se writes:

> Lars Magne Ingebrigtsen <larsi@gnus.org> writes:
>
>> Most of the image format decoders (jpeg and gif, for instance) do not
>> support image rescaling.  So shr uses ImageMagick for all its image
>> handling.
>>
>> There are two problems with this:
>>
>> 1) ImageMagick is crashy.  Virtually all Emacs crashes I get happen deep
>> in the ImageMagic code.  I mean, I don't get a lot of crashes, but they
>> happen from time to time, and are pretty annoying.
>>
>> 2) Some people run Emacs without ImageMagick built in, but usually have
>> the other libraries enabled.
>>
>> So I would propose to add a general image scaling function, and use that
>> in all the image handling functions.  Without image rescaling, Emacs is
>> pretty useless for anything that involves handling images.
>>
>> Does this sound OK to everybody?
>>
>> And if so, is there an FSF-copyright-assigned quality image rescaling
>> function out there that I could adapt to Emacs so that I don't have to
>> write it myself?  >"?
>
> Its a pity ImageMagic is crashy, but I take your word for it, since i
> dont experience it myself.
>
> Maybe something can be extracted from Gimp or Inkscape?
> Other than that, implementing a schoolbook image rescaling algorithm
> shouldnt be too much work.

OpenCV could perhaps be used as well. I have used it for mixing and
scaling of videostreams in the past, using affine transformations.

I have used GStreamer as well, but I dont know how good that is for
still image scaling.

Maybe the above libraries are too heavyweight, I'm just throwing the
ideas out there.

-- 
Joakim Verona

Re: Image rescaling

[Lars Magne Ingebrigtsen]

joakim@verona.se writes:

> I have used GStreamer as well, but I dont know how good that is for
> still image scaling.
>
> Maybe the above libraries are too heavyweight, I'm just throwing the
> ideas out there.

I was thinking that image rescaling wouldn't be, like, more than a
hundred lines of C code.  So no libraries at all; just some more code in
image.c.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Re: Image rescaling

[joakim]

Lars Magne Ingebrigtsen <larsi@gnus.org> writes:

> joakim@verona.se writes:
>
>> I have used GStreamer as well, but I dont know how good that is for
>> still image scaling.
>>
>> Maybe the above libraries are too heavyweight, I'm just throwing the
>> ideas out there.
>
> I was thinking that image rescaling wouldn't be, like, more than a
> hundred lines of C code.  So no libraries at all; just some more code in
> image.c.

Maybe fallback to nearest neighbour if one doesnt have/want imagemagic?
Thats maybe, uhm, 10 lines of code?


-- 
Joakim Verona

Re: Image rescaling

[Lars Magne Ingebrigtsen]

joakim@verona.se writes:

> Maybe fallback to nearest neighbour if one doesnt have/want imagemagic?
> Thats maybe, uhm, 10 lines of code?

And it looks like total crap.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Re: Image rescaling

[joakim]

Lars Magne Ingebrigtsen <larsi@gnus.org> writes:

> joakim@verona.se writes:
>
>> Maybe fallback to nearest neighbour if one doesnt have/want imagemagic?
>> Thats maybe, uhm, 10 lines of code?
>
> And it looks like total crap.

Yes.

-- 
Joakim Verona

Re: Image rescaling

[Stefan Monnier]

> 1) ImageMagick is crashy.  Virtually all Emacs crashes I get happen deep
> in the ImageMagic code.  I mean, I don't get a lot of crashes, but they
> happen from time to time, and are pretty annoying.

WIBNI we could fix those?

> Does this sound OK to everybody?

I'm not super-excited at the prospect, but I could probably live with it.


        Stefan

Re: Image rescaling

[Lars Magne Ingebrigtsen]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> 1) ImageMagick is crashy.  Virtually all Emacs crashes I get happen deep
>> in the ImageMagic code.  I mean, I don't get a lot of crashes, but they
>> happen from time to time, and are pretty annoying.
>
> WIBNI we could fix those?

It would be, but I don't really want to become an ImageMagick
developer.  >"?

>> Does this sound OK to everybody?
>
> I'm not super-excited at the prospect, but I could probably live with it.

Ok, I'll start looking at algorithms...

But if somebody else wants to implement this, please do be my guest. 

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Re: Image rescaling

[Dmitry Antipov]

On 09/16/2014 01:42 PM, Lars Magne Ingebrigtsen wrote:

> Ok, I'll start looking at algorithms...
>
> But if somebody else wants to implement this, please do be my guest.

If USE_GTK, why do not rely on gdk_pixbuf_scale?

Dmitry

Re: Image rescaling

[Lars Magne Ingebrigtsen]

Dmitry Antipov <dmantipov@yandex.ru> writes:

> If USE_GTK, why do not rely on gdk_pixbuf_scale?

Not all Emacsen er built with GTK, I think.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Re: Image rescaling

[Eli Zaretskii]

> From: Lars Magne Ingebrigtsen <larsi@gnus.org>
> Date: Tue, 16 Sep 2014 13:37:21 +0200
> Cc: Stefan Monnier <monnier@iro.umontreal.ca>, emacs-devel@gnu.org
> 
> Dmitry Antipov <dmantipov@yandex.ru> writes:
> 
> > If USE_GTK, why do not rely on gdk_pixbuf_scale?
> 
> Not all Emacsen er built with GTK, I think.

Well, not all Emacsen are built with ImageMagick, either, but you were
okay with depending on it, if it wasn't for its crashing.

The gdbk-pixbuf library is also available in Emacs build with RSVG
support, and we even already have code to make an image out of
GdkPixbuf objects in that case.  So I think Dmitry's suggestion is not
something to dismiss too easily.

Re: Image rescaling

[Lars Magne Ingebrigtsen]

Eli Zaretskii <eliz@gnu.org> writes:

> Well, not all Emacsen are built with ImageMagick, either, but you were
> okay with depending on it, if it wasn't for its crashing.

Well, I wasn't going to reimplement all of ImageMagick in Emacs, either,
so it's not really a fair comparison.

After looking at the algorithms, I think we may be talking about less
than 50 lines of C code vs relying on an external library not available
in all builds.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Image rescaling

[Stephen J. Turnbull]

Lars Magne Ingebrigtsen writes:

 > 1) ImageMagick is crashy.  Virtually all Emacs crashes I get happen deep
 > in the ImageMagic code.  I mean, I don't get a lot of crashes, but they
 > happen from time to time, and are pretty annoying.

That's a shame.  That's why we gave up on delegating image support to
ImageMagick in 1999 (or maybe a year or two later).

Has anybody tried GraphicsMagick for image support in Emacs (assuming
it's not somehow taboo for political reasons)?  Their original reason
for forking was to provide a more stable API and implementation.

Re: Image rescaling

[Eli Zaretskii]

> From: "Stephen J. Turnbull" <stephen@xemacs.org>
> Date: Tue, 16 Sep 2014 12:10:49 +0900
> Cc: emacs-devel@gnu.org
> 
> Has anybody tried GraphicsMagick for image support in Emacs (assuming
> it's not somehow taboo for political reasons)?

Glenn did, AFAIR.

Re: Image rescaling

[Ivan Kanis]

September, 15 at 14:45 Lars Magne Ingebrigtsen wrote:

> Most of the image format decoders (jpeg and gif, for instance) do not
> support image rescaling.  So shr uses ImageMagick for all its image
> handling.

Could you fix image orientation while you are at it? I have gotten a few
e-mail in gnus with images upside down. They were taken with smart phones
and the image orientation information is in the jpeg.

You can see the command jpegexiforient in Linux for more information.

Ivan
-- 
The rubber band broke.
    -- BOFH excuse #4

Re: Image rescaling

[Lars Magne Ingebrigtsen]

Ivan Kanis <ivan@kanis.fr> writes:

> Could you fix image orientation while you are at it? I have gotten a few
> e-mail in gnus with images upside down. They were taken with smart phones
> and the image orientation information is in the jpeg.

Yeah, 90/180/-90 degree rotation would also be nice, and is trivial to
implement.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no