Work with pseudocolor images in ArcInfo GRID

Summary

Pseudocolor images are a single band image with an indexed 'colormap' that matches a specific RGB color to a pixel value. When converting a pseudocolor image to a grid, you must specify a colormap, otherwise the grid will not be created.

Procedure

1. Use the DESCRIBE command to determine if the image uses a colormap. The returned Image Type should say: PSEUDOCOLOR.
2. Use IMAGEGRID to convert the image to a grid and to create a colormap file. Both output files will be created in the current workspace.
3. Process the grid. As long as the grid's values do not change the original, colormap will still be valid.
4. If the values of the grid change, you will need to modify the colormap file to reflect any changes. You can use any ASCII text editor to do this.
5. Use GRIDIMAGE to convert the grid back to an image. It requires the colormap file to create a pseudocolor image.
   
   An example:
   
   
   Arc: describe stcoll_drg.tif
   Description of Image stcoll_drg.tif
   
   Image Format : TIFF Image Depth = 8
   Image Type : PSEUDOCOLOR Image Bands = 1
   Image Colormap : TRUE Number of Columns = 4196
   Image Compressed : TRUE Number of Rows = 5518
   Image Rotated : FALSE Pixel Size DX = 2.520
   Pixel Size DY = 2.520
   
   BOUNDARY STATISTICS
   
   Xmin = 10535.451 No statistic information available
   Ymin = 194295.828
   Xmax = 21109.696
   Ymax = 208201.616
   
   NO COORDINATE SYSTEM DEFINED
   Arc: imagegrid
   Usage: IMAGEGRID {out_colormap_file} {in_band}
   {NEAREST | BILINEAR | CUBIC} {DEFAULT | SQUARE}
   Arc: imagegrid stcoll_drg.tif newgrid newgrid.clr
   Converting Image to Grid ...
   Arc: gridimage
   Usage: GRIDIMAGE {NONE | NOMINAL | GRAY | in_colormap_file}
   
   {BIL | BIP | BMP | BSQ | ERDAS | GRASS | IMAGINE | JFIF | RLC | SUNRASTER | TIFF}
   {NONE | COMPRESSION | G4 | LZW}
   Arc: gridimage newgrid newgrid.clr output.tif tiff
   Converting Grid to Image ...
   Arc: describe output.tif
   Description of Image output.tif
   
   Image Format : TIFF Image Depth = 8
   Image Type : PSEUDOCOLOR Image Bands = 1
   Image Colormap : TRUE Number of Columns = 4196
   Image Compressed : FALSE Number of Rows = 5518
   Image Rotated : FALSE Pixel Size DX = 2.520
   Pixel Size DY = 2.520
   
   BOUNDARY STATISTICS
   
   Xmin = 10535.451 No statistic information available
   Ymin = 194295.828
   Xmax = 21109.696
   Ymax = 208201.616
   
   NO COORDINATE SYSTEM DEFINED
   
   
   
   
   For more information on the types of images, see the ArcInfo Documentation (ArcDoc) Contents > Cartography > Image Integration > Introducing the Image Integrator > Image types.