IMG_TRUE8 Procedure

Generates a pseudo true-color image suitable for display on devices capable of displaying 256 simultaneous colors.

Usage

IMG_TRUE8, red_img, grn_img, blu_img, rgb_img, red, grn, blu

Input Parameters

red_img—A 2D image representing the red component of a true color image. red_img must be the same size as grn_img and blu_img.

grn_img—A 2D image representing the green component of a true color image.

blu_img—A 2D image representing the blue component of a true color image.

Output Parameters

rgb_img—A pseudo true-color 8-bit image that can be displayed using the TV procedure (see Discussion).

red—The red component of the color table.

grn—The green component.

blu—The blue component.

Keywords

None.

Discussion

The image generated by IMG_TRUE8 is suitable for display on devices with 8-bit planes of color. It is useful when you have Landsat type images that you want to merge into a true color system.

For correct appearance, rgb_img should be displayed in a graphics window with n colors allocated to it, where n is 256 under UNIX and 236 under Windows. For example:

WINDOW, 0, Colors = 256

Also, the proper color table needs to be loaded by using the command:

TVLCT, red, grn, blu, 0

where red, grn, and blu are the values obtained from IMG_TRUE8.

Then use the TV procedure to display the image:

TV, rgb_img

Note: On some systems it may be necessary to click in the image window to see the proper colors.

Examples

This displays a pseudo true-color Landsat image on an 8-bit color system.

PRO img_demo1
   ; Specify the window size.
   winx = 477
   winy = 512
   ; Set up the color components for the true color image.
   red_img = BYTARR(winx, winy)
   grn_img = BYTARR(winx, winy)
   blu_img = BYTARR(winx, winy)
   OPENR, 1, !Data_Dir + 'boulder_red.img'
   READU, 1, red_img
   CLOSE, 1
   OPENR, 1, !Data_Dir + 'boulder_grn.img'
   READU, 1, grn_img
  CLOSE, 1
   OPENR, 1, !Data_Dir + 'boulder_blu.img'
   READU, 1, blu_img
   CLOSE, 1
   ; For Windows, use "Colors=236" in the following line.
   WINDOW, 0, Colors=256, XSize=winx, YSize=winy
   ; Create and display the true color image.
   IMG_TRUE8, red_img, grn_img, blu_img, rgb_img,red, grn, blu
   TVLCT, red, grn, blu, 0
   TV, rgb_img
END

Note:

To see an example using the same data, except displayed in true 24-bit color on a 24-bit X workstation, see the PV‑WAVE User Guide.

For a comparison of pseudo- and true-color images, see the PV‑WAVE User Guide.