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How To: 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.
    [O-Image] Pseudocolor Image Processing
    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.

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