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:

Before

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



After

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.

Before

Figure 4.  An under illuminated scan, traditionally exhibited by a poor quality scanner.


After

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.

Before

Figure 6.  A CN Geep rests at sunset.


after

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.


Before

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.


After

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.



Before

Figure 12.  Our original image after photographed appears rather dark.



oversat

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.


after

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.


before

Figure 16.   A rather dreary image of 7498 rolling through Neenah.



mid

Figure 17.  After doing some color balancing, color saturation enhancement, contrast enhancement, and light gamma correction, the image is beginning to take shape.



after

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