PostGIS Raster : Extending PostgreSQL for The Support of ... - CoDE

Band Properties
Figure 6.12: Media area.
Depend on the number of bands that a map possesses, the Single band radio button (respectively
the Multi band radio button) will be marked if the map has only one band (multi band).
Figure 6.13: Single band rasters.
In the case of one band, each map is coded in gray color (a pixel color is coded either in RGB or
CMYK color models that require at least three band). However, user can load a color palette from a
style file created from color legend option. A style file describes each pixel value by a RGB triple in
each row. Example of rows in a style file is as follows:
"17.00592,139,0,116,255,
17.56223,137,0,118,255,
..."
The first number is a pixel value. The next three numbers are a RGB triple. The final number
is alpha value that indicates the transparency level between an image and a background. In this
example, 255 will create a full transparency.
To set up a color palette for a map from a style file, firstly QGIS uses the file to create Color Ramp
Entries array object and then set this object for the maps.
Pseudo code to set up a color palette:
Create Color Ramp Entries array object
For each loaded map
Tell the map to use a QgsColorRampShader function
Get a pointer to the raster shader function
Set parameters for the QgsColorRampShader function using Color Ramp Entries array
Refresh the map
In multi band case, as maps are already coded in either RGB or CMYK color models, then there
is no option to create a color table. Instead, it offers the possibility for user to choose a specific single
band for visualization or switch to multi band mode. By default, color maps are displayed in multi
band color mode. When single band color mode is activated and a band number is chosen, the function
mulSinBandCol is used to turn on only the chosen band and turn off the others band for all maps.
Pseudocode for mulMulBandCol:
For each loaded map
Turn the map on MultiBandColor mode.
For single band color, pseudocode of mulSinBandCol is:
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