POW and X Colormaps

POW allows some interactive manipulation of the Colortable used to display grayscale images. POW has detailed X Colormap handling options. There are four different ways of dealing with colormaps. The powColormap options are available in fv by using the "-cmap" command line argument to fv. The different options are:

  • 0 - let POW attempt to determine the optimum colormap setup for you. This is the default.
  • 1 - Force POW to setup a private colormap. POW will setup this colormap to minimize (but not eliminate) flashing.
  • 2 - Force POW to use truecolor. If you have a 16 or 24 bit truecolor visual available, this looks very nice, and allows different colortables for different images, but interactive changes to the image colortable are slow. If you only have 8 bit truecolor, this will look pretty bad.
  • 3 - Force POW to use the screen default colormap. This guarantees no flashing, but may force truecolor image mode to be used with an 8-bit visual which looks really awful.
Generally, if you experience colormap problems, mode 1 is probably the most robust unless you don't have any pseudocolor visuals (e.g. a Linux machine running in 16 or 24 bit mode).

The POW Color Menu

The POW Color menu has four parts:

  1. The top section contains three hierarchical menus listing a bunch of colortables from which to choose. They are divided into Continuous (colors vary in a smooth manner), Ramps (colormap is divided into separate colors within which the intensity varies from dark to bright), and Steps (colormap is divided into blocks of a constant color/intensity).
  2. You can reverse the "dark to light" direction of your colortable by checking the Invert Colortable button.
  3. There are four scalings of the colortable available in the next section. The first three linear, sqrt, and log apply the indicated function to the color table. The next item -- Histo Equalize -- will compute a histogram of an image (within a user-configurable range) and attempt to distribute colors equally amongst the pixels. The Rescale Image command allows the user to define what intensity range over which to apply the color table. The window which comes up contains the original and current intensity range and a histogram of the current image. A new range can be either typed in directly or selected using the histogram.
  4. The final item -- Create Colorbar -- will create a new graph containing a colorbar for the current image.

You can interactively change the contrast and brightness of the current image's colortable by dragging the left mouse button across the image.

Pages maintained by Bryan Irby
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