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Enhance an image with the Curves feature of the GimpEvery photo can use a little bit of touching up before printing.
A little bit of cropping, brushing out errant objects, adjusting
brightness and contrast, the list of possible enhancements goes on and
on. Most cameras come with some basic software to edit
photos. However, few of these packages offer the options
available in a full featured graphics editor like Photoshop, Paintshop
Pro, or, the Gimp.
This article will look at my favorite adjustment to photos - the curves
color adjustment. That's the name in the Gimp, other packages
will have a similar feature with a somewhat similar name.
Some Gimp background
We are using the Windows port of the Gimp for this article.
Specifically, we are using the "Unstable" Installer Packages for
Windows that are made available for download, here. Do not be too
scared about the "Unstable" disclaimer - at the time of writing, I have
had no problems with this release. It is much improved over the
"stable" Windows release in all respects, including user interface,
features, and ironically, stability - we've had no crashes of the
software... yet. By the time you read this, a final Windows
release of Gimp v. 1.3 may be available.
We use the Gimp for a few reasons. First, the Gimp is Open Source
Software, like Linux, it is absolutely free to use, and in fact, free
for you to modify, if you so desire. Second, the Gimp is more
than capable enough for home use - and much corporate use. It is also
available on multiple platforms, Windows, Linux, and others. The Gimp
website is at gimp.org.
Remeber, all advanced graphics packages will offer the color adjustment
that is used in this article, so if you wish to use an alternate
package please do so - and post about it in our forum!
Preparation
Before reading on, remember to calibrate your monitor! Adjusting the
colors in an image requires that your monitor and computer be
configured to correctly render your images, or else you will be making
color changes to the wrong visualizations! We have an article
covering calibration
and a few other preparation tips.
The Too Dark, Original, Image
Here is the image that I will use to demonstrate the curves
feature. It's a photo of the new gate into Vancouver's Chinatown.
Please excuse the jpeg compression artifacts, we don't have the budget
to serve 1 MB jpeg's here!
So, this image isn't all that great. The gate, the most important
part of the photo is too dark - it looks like the auto exposure system
of the camera got "fooled" by the bright sky in the background.
I'll try to save this photo with the curves adjuster.
The Gimp Curves Dialog
You can open this dialog (once your image is opened) from the "Tools"
menu option, then "Colors", then "Curves" of Gimp 1.3. When you
first open the dialog, it displays a diagonal line from the left-bottom
to the top-right corner. The curve shown in the screenshot below
is the one I used on the photo above.
The general idea behind the curves, is that the full range of
brightness of your current image is laid along the horizontal
axis. The final, adjusted, brightness is adjusted along the
vertical axis. For example, if you were to move the top rightmost
point of the line "down", the brightest portions of your image,
lightbulbs or candles for instance, would "darken" somewhat while the
rest of your image would be relatively unchanged. Trust me, it
makes a lot more sense once you have tried it for yourself.
In this case, I've attempted to increase the brightness of the
lower-midtones of the image above. This should leave the sky
more-or-less untouched, unlike a simple contrast and brightness
adjustment! Remember that nothing is for free, adjusting the
image with this feature will often make images look better, but it
isn't magic. Use some common sense when applying this or any
other image filter.
A screen shot of the Gimp Curves dialog:
The curve adjusted image
It looks better to me. What do you think? I had wanted to
push the brightness up a bit more, but the result started to look a
little too grainy for my taste. As always, your mileage may vary.
Closing words
That's it! The curves adjustment is a lot more advanced than the contrast and brightness changes. Trying to brighten up the subject of this photo by increasing the brightness would have washed out the skies! In Vancouver, where we get clouds, clouds, and often rain, it is almost illegal to destroy any blue skies that we are lucky enough to capture in our photos. I find this feature to be great at turning bad photos
into passable ones, and passable photos into good ones. I hope you do too.
Please visit our forums and post your experiences with the Gimp or other software packages, and editing your images.
Leonard Copyright © by My Photo Printer.net. All Right Reserved. Published on: 2003-10-28 (7301 reads) [ Go Back ] |
