Transparent rgb pixel when all 3 values of original pixels are below browse_type min and no-data is set to 0

[lubojr]

Problem: When all three original band values are below their respective browse_type minimum stretch values, final pixel is made transparent when no-data is set for the bands to 0.

Reference:
https://gitlab.eox.at/esa/prism/vs/-/issues/107

stretch with dim_range 50 255, 50 255, 50 255

stretch with dim_range 45 255, 45 255, 45 255

Maybe this piece of code is where it takes place

eoxserver/eoxserver/render/mapserver/factories.py

Line 864 in 2b85259

return gdal.GDT_NUMERIC_LIMITS.get(field.data_type) or (0, 255)

[jankovicgd]

found a workaround for some usecases.

With byte data it is possible to define something like:

TRUE_COLOR:
  asset: multispectral
  red:
    nodata: null
    expression: red
    range:
      - -1
      - 255
  green:
    nodata: null
    expression: green
    range:
      - -1
      - 255
  blue:
    nodata: null
    expression: blue
    range:
      - -1 
      - 255
  alpha:
    expression: a
    range:
      - 0
      - 255

If the lower bound is 0 it is excluded as nodata and made transparent even if 0 is not actually a nodata value. Setting -1 as the lower bound includes 0 as data, meaning at some point it is exclusive at the lower bound (maybe also upper)

[lubojr]

Fixed by #550 and #546

• Needs a database migration to be run to add show_out_of_bounds_data on BrowseType model

For operators:

To circumvent problem in this issue (masking exactly black 0,0,0 pixels to transparent), use the --show-out-of-bounds-data flag when creating a browse type.

This will use the LUT[_n] rendering. https://mapserver.org/id/input/raster.html#special-processing-directives which sets browse_type.band.nodata value to 0 in respective final color representation (rgb) and maps browse_type.band.nodata+1 to 1 and browse_type.band.min to 1.

This rendering mode can be used only on UInt8 and UInt16 (and positive floats up to UInt16 range) because of how LUT is implemented -> The in values must be in increasing order. The range of input values can go from 0 up to 65535.