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Problem: IKONOS 11-bit panchromatic images appear noisy

Description

IKONOS 11-bit panchromatic images display as 'noise' or 'salt and pepper' in Workstation ArcInfo.

Cause

This is a result of the wrapping of the 256 value black-to-white greyscale ramp to cover the 0 to 2048 value range of the input image.

Most display devices are limited to 256 shades of gray, so having 2048 possible values in the data would provide no benefit. The larger range of values is only really useful for spectrographic analysis.

Note that the 11-bit data is packed into a 16-bit image file. That is, the image values are packed into the first 2048 values, with the remainder (up to the maximum of 65536) being unused.

Solution or Workaround

  • Option 1:
    Obtain the 8-bit versions of the images from the vendor.

    The 0-255 range of the 8-bit versions of the data will display correctly.

  • Option 2:
    Convert the 11-bit TIFF to an 8-bit TIFF.

    1) Convert the image to a grid:

    Code:
    Arc: IMAGEGRID iko_11 img_grd

    2) Reduce the range of values from 0-2048 to 0-255 with the GRID SLICE function:

    Code:
    Grid: iko_slice = SLICE (img_grd, EQINTERVAL, 256, 0)

    3) Convert the reduced grid to an image:

    Code:
    Arc: GRIDIMAGE iko_slice # iko_8 TIFF

    The output here is an 8-bit TIFF image that should display correctly in ARCPLOT.

  • Option 3:
    1) Convert the 11-bit TIFF to a BIL/BIP/BSQ

    The BIL, BIP and BSQ formats can display a 16-bit image without the same problems TIFFs experience. They support a statistics file, which will instruct ARCPLOT to apply a linear stretch to fit within the display range of 0-255. The statistics will be calculated when the image is converted to a grid.

    2) Convert the image to a grid:

    Code:
    Arc: IMAGEGRID iko_11 img_grd

    3) Create the output as a BIL (or BIP or BSQ) format:

    Code:
    Arc: GRIDIMAGE img_grd # iko_bil BIL