Pseudo

A pseudo-colored image is derived from a grayscale image by mapping each pixel value to a color according to a specified color palette.  For example, a color palette could be defined and applied to the range of intensities in a standard 8-bit image (0-255) such that each value in that range displays a different color.  When applied to the grayscale image, the lighter grays will, for example, appear yellowish to reddish, and the darker grays will appear bluish to purplish.  Pseudo-coloring is useful for making details in an image more visible by increasing the distance in color space between successive gray levels.

When you click on the Pseudo tool, a dialog box appears that provides the following controls you can use to pseudo-color your image.

Pseudocolor On/Off:  Check/uncheck this box to enable/disable the pseudo-color feature.  This box must be checked for pseudo-coloring to be applied to an image.

Spectrum:  Color palettes, for the purposes of the pseudo-color feature, are defined as spectrums -- color continuums that map a gradual shift from one color space to another or from black to a color.  The Spectrum field allows you to select the type of spectrum you want to use.  

Type: This control is only relevant if you select "Custom" in the Spectrum list box.  The Type pull-down list box allows you to define the color model to use for defining a custom spectrum.  This selection works in conjunction with the Start and End color picker controls.  The Type selection specifies the method of color transitions and the Start and End color picker controls specify the colors to transition from and to using the selected method.  

  • Select "RGB" to create a color palette that transitions directly from one color to another.
  • The "HSI" (Hue Saturation Intensity) options allow you to use the ROYGBIV color model for defining palette color transitions.  If, for example, you select HSI CCW (counter clockwise) and you select Red for the Start color and violet for the end color, the color palette is updated to display the entire rainbow (ROYGBIV).  

    Alternatively, you can select only a portion of the rainbow by selecting colors in the middle of the ROYGBIV continuum, such as yellow and blue.  In this case, the color palette is updated to show transitions from yellow to green to blue.
  • Select "Custom" to define a custom color palette based on a user-defined series of color bands.  See Creating a Custom Color Palette below for instructions.
     

Start - End:  The Start and End spin boxes specify the start and end pixel values that define the range for which you want the pseudo-color palette applied.  For example, perhaps you are only interested in colorizing intensities within the range of pixel intensity values from 100 to 200.  The Start and End controls allow you to apply the palette to only that range.  To apply a palette to the entire image, Start should be "0" and End should be the greatest value of the intensity range ("255" for an 8-bit image).

Divisions:  In this spin box, specify the number of individual colors to include in the palette.  For example, if you specify "256" for an 8-bit image that has intensity values ranging from 0 to 255, there will be one division -- one color -- for each possible intensity value.  

Spins:  The value you enter here controls how many times the palette is repeated across the available range of pixel intensity values.  

Options:  Click on this tool to reveal the following options menu:

  • Combine with BCG: Select this option to have brightness, contrast, and gamma adjustments reflected in the pseudocolored image.  If not checked, BCG adjustments are ignored for the purposes of pseudocoloring images.
  • Auto Scale for new Types:  Select this option to have Image-Pro automatically scale palettes' Start->End ranges according to the active image's bit depth.  For example, if a palette was defined for an 8-bit image with a range of 0-255, but then you switched to a 16-bit image, then the palette would be automatically scaled up to a range of 0-65535.  If this option is not checked, palette definitions' Start and End values are treated as absolute values.  
  • Extend Colors:  Select this option to extend the Start and End colors above and below the Start and End values.  For example, if the Start color is red, and the Start value is 15, then selecting this option extends the red to include the values 0-14 as well.  If not selected, then pixels with values between 0 and 14 would be colorized as black.
  • Sync with Display Range: Select this option to have the pseudocolor palette automatically scaled to fit the pixel range defined by the active image's black level (BL) and white level (WL) values.  This option makes the BL and WL adjustments reflected in the pseudocolored image.  If not selected, the BL and WL adjustments are ignored for the purposes of pseudocoloring the image.

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Creating a Custom Color Palette

To define a custom color palette:

  1. From the Spectrum pull-down list box, select "Custom."
  2. From the Type pull-down list box, select "Custom."
  3. In the Divisions spin box, enter the number of color bands you want your custom color palette to have.  
    The spectrum display is updated to display the specified number of bands.  For example, if you type "4," the spectrum displayed is updated to show four distinct color bands:
  4. Click on the left-most band to select it, or, enter "1" in the Index spin box.
    The band is selected, as indicated by crop marks.
  5. Click on the Color Picker tool at the Start control to select the color you want representing the selected band.
  6. Repeat the previous two steps for each band in the spectrum.