Re: [GM-core] GM -normalize without clipping highlights

[Bob F. <bfr...@si...>]

On Tue, 20 Jul 2010, Charlie De wrote:

> If the only way to overcome highlight clipping that GM -normalize produces is to
> write a script, then I'll stick with what I've done.  It's relatively fast and
> has the benefit of bringing in IM's colour balance, which helps when GM gets it
> wrong.  It does happen, on a picture of a girl in a park, with green foliage
> behind her, GM -normalize tinted the whole picture green.  IM's

I don't think that GM should have tinted the picture green unless the 
actual data was already tinted green (might not have been noticeable). 
The -equalize option is different since it normalizes each channel 
independently and can result in changed colors.

Modern GraphicsMagick has some other features as well.  For example, 
the -asc-cdl option can be used to apply a change to the image, but 
you need to know the best parameters to apply for your images.  This 
capability is used by the motion picture industry.

If your images are similar enough, you could use the Hald CLUT 
(-hald-clut) feature to apply the same correction to many images based 
on the manual correction applied to an identity image.

> ">From what I have seen, 'dcraw' has the best access to the camera raw
> data information (including proprietary camera metadata) so it will
> always be more competent at applying automatic corrections than
> follow-on software like GraphicsMagick."
>
> Not in my tests!  Dcraw may have best access to raw data, but once that data is
> decoded, the data is like any other 16bit file.  And in all the extensive

When Glenn and I spent some time applying dcraw to some raw image 
files he had, we found that some versions of dcraw worked much 
differently than others.  Dcraw is very tiny so I compiled various 
versions until I found the one which worked best for his files.  It 
may sound nuts but you could have a directory with about 30 dcraw 
executables in it and try each one until you find the one which 
produces the best result.

> Thanks for listening, I hope I've given you some food for thought as 
> you develop things down the line.

Automatic correction is a real art.  Results depend on each image.  I 
used to like the automatic correction supplied by a Kodak software 
package until I found that it was irreparably eliminating attractive 
dark shadows and increasing the visible noise in JPEG files.  It also 
caused images taken with a flash to look like they were taken with a 
flash.  The algorithm increased visible detail, but also removed all 
artistic appeal from the image.

Bob
-- 
Bob Friesenhahn
bfr...@si..., http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/