Histogram

The Histogram Functions modify an image or a selection within that image based upon its luminance histogram.

So where do I find this luminance histogram..... and what is it?

The Histogram Window can be opened by clicking on the histogram toggle switch located on the toolbar.

The Histogram Window doesn't do anything in and of itself, it's a tool designed to help you decide what you need to do to improve your image. The histogram window displays a graph of the color values of the active window. The display is usually in RGB and the luminance. Zero luminance is black while full luminance is white. The numbers at the top of the window display the number of pixels that match the histograms max., min., and average values. The spectrum for a color is on the horizontal axis while the portion of the image's color that matches that spectrum is displayed on the vertical axis.

The check boxes at the bottom allow you to turn off the graphing of certain colors or the luminance. Click on the red check box in the histogram window to the left to see how the graph displays with the box unchecked.

Alright already ! If the Histogram Window doesn't do anything...... What does??

There are two Histogram Functions within Paint Shop Pro, the Equalize Function and the Stretch Function.

To apply one of the functions to the active image:

Select either a portion of your image, or activate the entire window, depending on which you want to modify.
Select "Histogram Functions" located under Colors on the Menu bar
Select either Equalize or Stretch from the submenu.

Equalize Histogram Function: Smooths or evens out the histogram resulting in an averaging of the image or selection brightness.
Stretch Histogram Function: If the histogram doesn't cover both ends of the spectrum, that is, both black and white, then the Stretch function will adjust the luminance so that the entire spectrum is encompassed.

So now that I know all this...... what can I do with it??

The best way to learn about this function is to experiment with it. Try selecting different areas of an image and applying the functions, then comparing your results. Always remember to work off of a copy of your original image so you don't accidentally alter your original. Copies are easy... with the original image selected, press shift+D on your keyboard a few times. You'll have several copies of your original now, so close the original to safe-keep it.

Some examples of the Equalize Function

unaltered image

Original picture, taken with an old Pentax SLR, the negative transferred to cdrom PCD format, and converted to jpg. (ok... so it was a new Pentax, but it's old now since the picture was taken in 1967) :)

gwb selection area

For this example I selected an area of the sky using the magic wand, tolerance set to 20, feather set to 9. I had to hold in the shift key to include the area inside of the bridge girders in the selection.

gwb/selected area/equalized

Applying the Equalize Function to the selected area gives a nice highlighted affect, and accents the bridge. I applied a soften affect to the highlighted area using the retouch/soften tool, taking care to not retouch the bridge. This removed the splotchiness around the highlighted areas edges.

selected area inverted and equalized

With this example, I took a slightly different approach. Using the magic wand tolerance set to 20, feather set to 0, I selected the black 'tree' area of the image. I then inverted the selection and applied the Equalize function, resulting in everything but the trees being equalized.