Lesson 3 - BRIGHTNESS, CONTRAST, GAMMA, AND THE CLARIFIER
In this tutorial, we'll review some of the most basic commands
that Paint Shop Pro has to offer. Understanding the first couple of
commands should be second nature since we have similar adjustments on our
televisions and computer CRT's. The latter set involve a slightly more
complex algorithm, but fortunately are still fairly straightforward.
Brightness and Contrast Adjustment
Often after scanning an image, you may notice that
your scanned image is somewhat darker than what you had hoped to acquire.
Likewise, your image may be lacking the full range of luminance (i.e.
the whites are completely white and the blacks aren't completely black).
The Brightness/Contrast Adjustment 
(located under Colors >> Adjust >> Brightness/Contrast) can
usually be of assistance. With this command we can perform reasonable
amounts of luminary correction for scanner errors, and even difficult photography
lighting situations. Let's explore a couple of examples.
First, let's say for instance Mother Nature sticks us with a hazy
overcast day for our sight-seeing vacation. Your pictures exhibit the
characteristic grayed out, flat appearance. Not very interesting to
say the least. By increasing the brightness and the contrast, we can
enhance the overall look to something more like what we may capture on a
fair weather day:
Figure 1. The Sturgeon Bay Canal pier head light on a not so nice day. Lots of gloom, but very flat.
Figure 2. Using the Brightness/Contrast adjustment tool, we can increase
the brightness and contrast to enhance the overall appearance
Figure 3. Our image after brightness/contrast adjustment makes our
two photographic subjects stand out more from the uniform background. This
image is now ready for further adjustment with tools such as the color correction.
Now let's consider you scanner just doesn't want to make life easy
for you. Under illuminated scans seem to be common, particularly among
bargain scanners, such as the author's. Never fear, a fairly liberal
application of a brightness increase brings levels back to where they need
to be.
Figure 4. An under illuminated scan, traditionally exhibited by a poor quality scanner.
Figure 5. Using the brightness/contrast adjustment, the majority of the point of interest can be recovered.
Now is a time to bring up a key point about digital images in general.
Just because wanted detail appears lost to the darkness doesn't necessarily
mean that it's not present. This is true for both scanned and digital
images. Here's why. Unlike the printed image, most monitors
have a difficulty displaying true black. If you need any more proof
of this, blank your screen with full black, turn off the lights and watch
how your monitor will still illuminate the room. As a result, many
monitors do a poor job of showing any differentiation in very dark colors.
However, the detail may actually still be there! A quick experiment
with the brightness/contrast controls may reveal whether the detail
is present or not, and whether it's worth attempting to recover.
Figure 6. A CN Geep rests at sunset.
Figure 7. By bringing up the contrast and brightness levels, we
can see that there's plenty of under frame detail hiding in the shadows.
Note for demonstration purposes, the levels have been somewhat exaggerated.
Before we move on to our next topic of adjustment, there's one more
tool to take into consideration for those who prefer more automatic means.
That tool is the Auto-Enhance Contrast tool 
. This tool is quite handy for those who are just starting to get
their feet wet in the realm of contrast adjustment. Although it works
quite well most of the time, be forewarned that even PSP can once in a while
misinterpret the levels and can sometimes overdo the enhancement, especially
on overcast photos. Not a big problem though, you can simply undo the
enhancement, and run the tool again, this time selecting a milder correction.
Figure 8. Back to our CN Geep again. This time let's try the auto-enhance contrast tool
Figure 9. The auto-enhance contrast tool simplifies the options by
basically allowing the user to choose three preferences. A lighter bias will
result in a lighter resulting image and vice versa. Strength does what
it implies and controls the strength of the tool. Appearance increases
or decreases the overall amount of contrast applied.
Figure 10. Our resulting image after the auto-enhance contrast. Note
once again the detail revealed that was previously shrouded in darkness (albeit
grainy). The tool has also perhaps over corrected somewhat, note the
shadow of the photographer in the bottom center cast by a nearby street light.
GAMMA Correction
No, this is not a form of Greek discipline, or a resulting
fraternity restitution, but a really handy tool for those images that do
manage to span the full range of luminance but just seem to come out dark
nonetheless. The Gamma Correction tool 
similar to the brightness tool, but instead of affecting all luminance
values in the image linearly (i.e. all values up or down by the same amount),
it focuses its attention most on the middle values. This is important
when trying to bring up the overall brightness of the image without over
saturating light areas, and also trying not to wash out dark areas.
Figure 11. The Gamma correction tool control. Note
the graph on the lower right represents input vs. output and the lines always
terminate at opposite corners. The adjustment bows this line according
the magnitude of adjustment. Gamma correction can be done by each separate
RGB channel if desired.
Figure 12. Our original image after photographed appears rather dark.
Figure 13. By using the brightness/contrast adjustment, the image
appears closer to expected brightness, but now the sky and the white tank
car are washed out.
Figure 14. By using a Gamma correction of 1.50, followed by a mild
contrast adjustment of 15%, we can brighten the image, but maintain the sky
color, the tank car details, and even keep a fairly strong shadow in front
of the locomotive.
It's worth noting that the Gamma correction tool is useful on overexposed images as well.
HISTOGRAM ADJUSTMENT
The Histogram Adjustment 
is a more advanced user tool, but it is worth noting if you find yourself
often doing the adjustments covered so far. The beauty of this tool
is it wraps up the brightness, contrast and gamma correction all into one
tool, and offers a little more intimate control of the results.
Figure 15. The histogram adjustment tool. The gray
graph represents (in this case) the number of pixels with respect to increasing
luminosity (i.e. more gray on the left means a darker input image,
more gray on the right means a lighter input image). The line indicates
the correct, similar to the gamma correction graph. Gamma correction
is controlled numerically, or by moving the center gray triangle. Contrast
is essentially (but not entirely) controlled by the slide on the right. Brightness
is controlled through the use of the minimum and maximum input and output
adjustments on the left side and the bottom. Like the Gamma correction
tool, the histogram tool can control RGB channels independently if desired.
CLARIFICATION
What?? You still don't get it? More clarification?
(Just kidding). Our final tool of discussion for this lesson is the
Clarifier 
This subtle, yet handy tool will put the finishing touch on your
image to help make your subject stand out. Essentially, it is a contrast
enhancement that focuses more on edges than just the image as a whole. It
is often used in conjunction with the sharpen and unsharpen mask tools. The
tool itself is quite straightforward to use, having only one adjustment,
which is a strength control with a range of 1 to 5.
Figure 16. A rather dreary image of 7498 rolling through Neenah.
Figure 17. After doing some color balancing, color saturation enhancement,
contrast enhancement, and light gamma correction, the image is beginning
to take shape.
Figure 18. The Clarifier tool helps give the image one final "boost" bring out the photographic subject.
In this lesson, we've explored a few of the more fundamental
image adjustment tools. These tools are useful for virtually
any image source, whether they are scanned, digital, or otherwise acquired.
Using these tools, you can correct for difficult image acquisitions,
poor lighting conditions, or some of the common minor photographic errors
resulting from incorrect shutter, aperture, or ISO setting. Like many
photo adjustments, the results are subject to the preference of the editor,
and settings will vary from person to person...even day to day with some
people. The best advice is to go with what you like. Preference
is much like the photographer's chosen composition, and it's an expression
of their individual style.
Until next time, happy experimentation.
-"Evil" Ray
©2003 Ray Meyer
http://www.n9pby.com