LUT

Description

LUT adjusts pixel values of a raster by passing it through a lookup table (LUT), and then writes the resulting imagery to disk. This allows bulk-radiometric enhancement of image data.

Parameters

Name	Type	Length	Value range
Input: Input raster layers *	Raster port	1 - 1024
InputLUT: Input LUT segments	LUT port	0 - 1024
Area Mask: Area mask	Bitmap port	0 - 4
Output: Output raster channels	Raster port	0 - 1024
Data Type	String	0 - 1	8U|16S|16U|32R Default: 8U

* Required parameter

Parameter descriptions

Input: Input raster layers

The channels to be enhanced with LUTs. Each input channel requires a corresponding LUT to be specified and will result in one output channel.

InputLUT: Input LUT segments

The input segments that contain the LUTs to use for image enhancement. Both basic LUT (type 170) and break-point BLUT (type 172) segment types are supported. If not specified explicitly, the default LUT of the input channel will be used automatically when it is identified by the DEFAULT_LUT_REF metadata tag. If an input channel does not have a default LUT defined (and no LUT was specified), an error will occur.

The elements of this parameter correspond to input channels by position. Unless relying on default-LUT metadata, one LUT must be specified for each input channel.

Area Mask: Area mask

The areas of the data to be processed. When no mask is specified, all pixels are processed by default. However, when a mask is provided, only pixels within the mask area are altered. When writing to a new output channel, the unmasked pixels are assigned NoData values. When writing to an existing channel, the unmasked pixels are not processed, and the values in the output channel are preserved.

With a bitmap mask, you specify the number of the bitmap segment you want to use. All of the pixels in the specified segment having a pixel value of 1 define the area where input data must exist to be processed.

Output: Output raster channels

The output channels to receive the enhanced raster.

Data Type

The data type of all output channels to be created. By default, LUT will create 8U output, which is sufficient in most circumstances; however, you can specify a higher bit depth with the DATATYPE parameter, if necessary.

When outputting to 8U, the LUT is applied to the input data, and the resulting value is written as an integer to the output channel. When outputting to 16U or 16S, the LUT is applied to the input data. The derived values are then stretched linearly over the full range of the output channel. When outputting to 32R, the LUT is applied to the input data, and the resulting value is written as a real number to the output channel.

Details

With remote-sensing applications, the intensity values of the original raw data are typically left unchanged. Enhancements (to aid in making visual interpretations) are applied using LUTs on the display system.

At times, however, it becomes necessary to permanently enhance the data by physically passing it through the LUT and writing it to disk. This removes the need for the LUT. Typically, this is done when preparing to export the data to another system, or to create a finished product that will be printed.

LUT transforms a set of image channels using a set of LUTs stored in LUT segments (LUT segment type 170 or BLU segment type 172). The transformed image data is stored in a set of output image channels. This allows bulk-radiometric enhancement of image data.

The MASK parameter specifies the area in the input channel that will be processed. Only the area under the mask will be processed; the rest of the image will be set to NoData when outputting to new channels or simply unaltered when writing to existing output channels.

Any pixel that is nodata in the input will be NoData in the output. Also, any pixel that is outside of a specified mask will be set to NoData when creating new output channels. When NoData is required for a new output channel, it will be the minimum of the bit depth of the output channel. The other pixel values will be increased so legitimate pixels are not mapped to NoData. When writing to an existing output channel, if that channel has NoData defined, that value will be used for the output NoData, and only when NoData is not defined will the minimum value be used.

Algorithm

The following is an example of the actual operation performed by LUT:

                         level  Output
    1   3   1   1          0      9            6   0   6   6
    3   3   3   0          1      6            0   0   0   9
    0   1   0   0          2      1            9   6   9   9
    3   3   0 255          3      0            0   0   9   0
                           :      :
                         255      0             
        Input                LUT                  Output