Carol Spears wrote:
On Sat, Aug 26, 2006 at 04:57:26PM -0700, Tom Williams wrote:
Anywho, when I do an "auto" levels adjustment on the photo, the result
looks quite a bit different and not as good as the original. I'm
wondering if the result is actually correct or not.
i do not know what the auto portion does for this tool. i assume it
does something like determining the lightest color and it turns that to
white and similar with the darkest color and black. i assume this
because that is how the little eye dropper thingies work with the levels
dialog.
Ok.
Here is the original image:
http://www.bay-online-media.com/tom/gimp/bay-bridge1.jpg
Here is the image after the "auto" level adjustment is performed:
http://www.bay-online-media.com/tom/gimp/bay-bridge1b.jpg
i actually enjoy playing with the levels tool and photographs, so i
endulged myself:
http://carol.gimp.org/files/bay-bridge1-levels.jpg
Looks great! :)
The original image was scaled to 1024x768 resolution at 72 dpi. The
original photo was taken at 72 dpi.
Is the resultant image correct? If so, why does it not look as good as
the original?
if you look at the different channels in the levels dialog, you can see
what the Auto button did. it consistently moves the light side to where
the color histogram starts for all three of the color channels. and it
seems that the gray (center) triangle stays in the middle of the other
two triangles.
i have no idea if this works for a majority of photographs or not.
i used the tool just on the "Values" Channel (which is not a real
channel) and i like mine better than your original and also the auto
adjusted image. to me, the only thing that was wrong with your
photograph was that 'all over gray' haze that scanned photo prints would
really get and digital photographs still seem to get somewhat.
Thanks for the detailed explanation. Obviously, I didn't understand
what the "auto" button did on the Levels dialog. I figured it would
automatically adjust color levels to be "correct", based on the photo
being edited but clearly I was wrong. :)
Now I have a better understanding of how to use that Levels dialog so
I'll do more experimentation with it and other photos.
Thanks! Yes, you did answer my question as did the other person who
responded off-list.
Peace...
Tom
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