[PATCH] Image sharpening function for ext/gd

There's new function in PHP 5 CVS, `imagefilter()`,
I'd guess this would be good addition into that one..

--Jani

Hello,

I was surprised to find that, although the GD image-handling functions
shipped with PHP do many useful things very well, there's no function
to sharpen an image. I found a few posts bemoaning this absence, and
therefore attach a patch which adds the function

int imagesharpen ( resource im, int pct )

It performs the sharpening in-place. pct is the degree of sharpening to
be applied: 0 does nothing; 100 gives a quite noticeable effect. Values

100 can be used for stronger sharpening. Negative values are treated
as 0.

The routine only sharpens truecolor images, as it rarely makes sense to
attempt the operation on palletted images.

It's a simple linear sharpening routine using a 3x3 kernel, rather than
the more flexible, but slower, unsharp masking approach used in e.g.
Photoshop, Imagemagick. However it's very effective at making resampled
photographic images (such as thumbnails) look a little more crisp.

I've built and tested it using gcc 3.3 under Mac OS X 10.3.1. There's
nothing I'd expect to be platform-dependent in it. The attached patch
is against php4-STABLE-200311202030, but it should work with most
varieties of php-4.3.4, as the new code is fairly self-contained.

This is my first patch for PHP. Is there anything else I should do,
beyond posting it here?

Many thanks,

Paul.

Second attempt at posting, this time hopefully with the patch as a MIME
type that won't be stripped...

Hello,

I was surprised to find that, although the GD image-handling functions
shipped with PHP do many useful things very well, there's no function
to sharpen an image. I found a few posts bemoaning this absence, and
therefore attach a patch which adds the function

int imagesharpen ( resource im, int pct )

It performs the sharpening in-place. pct is the degree of sharpening
to be applied: 0 does nothing; 100 gives a quite noticeable effect.
Values >100 can be used for stronger sharpening. Negative values are
treated as 0.

The routine only sharpens truecolor images, as it rarely makes sense
to attempt the operation on palletted images.

It's a simple linear sharpening routine using a 3x3 kernel, rather
than the more flexible, but slower, unsharp masking approach used in
e.g. Photoshop, Imagemagick. However it's very effective at making
resampled photographic images (such as thumbnails) look a little more
crisp.

I've built and tested it using gcc 3.3 under Mac OS X 10.3.1. There's
nothing I'd expect to be platform-dependent in it. The attached patch
is against php4-STABLE-200311202030, but it should work with most
varieties of php-4.3.4, as the new code is fairly self-contained.

This is my first patch for PHP. Is there anything else I should do,
beyond posting it here?

Many thanks,

Paul.

--
Paul Troughton http://paul.troughton.org/
mobile +44 7866 041144 home +44 1223 366900