[TYPO3-core] RFC #8878: Bug: Fix cropscale behaviour for transparent GIF

[Felix Buenemann]

Jigal van Hemert <jigal at xs4all.nl> wrote:
> Hi,
> 
> On 8-8-2010 15:46, Steffen Ritter wrote:
>> Since we require gd2 we probably should have a look in what we can do
>> without an external tool at all... in sprite-generator I found out
> > that
>> the gd variant was much faster than external tools.
> 
> I think that you'll find out that GD is very limited in its
> possibilities and that it is not very easy to obtain good results with
> it.
> 
> I'm currently trying to make GD produce transparent PNGs with an alpha
> channel, but this proves to be rather complicated.
> Transparency is handled either as "combine both pixels with full
> transparency, but the result is fully opaque" or as "overwrite the
> original pixel, but keep full transparency".
> 
> You can apply a matrix to an image to get effects like blur, unsharp
> mask, but these are limited to a 3x3 matrix (imageconvolution).
> 
> Also the quality of resampling is not as good as the various advanced
> algorithms in IM/GM can produce.

Yea, one problem Jpegs in TYPO3 alway look worse than those from
Photoshop is because glib uses libjpegs default chroma subsampling of
4:2:0 instead using the much crisper 4:2:2 sampling at lower compression
ratios.
That's why jpegs don't seem to look better when you crank up
jpeg_quality.

Imagemagick uses different subsampling depending on compression ratio.

-- 
- Felix Buenemann