[gdal-dev] More information to understand ColorTables in GeoTiffs

[Robert Nix]

Let me adjust my question. I changed the color-table code to:

c = gdal.ColorTable(gdal.GCI_PaletteIndex)
n = c.SetColorEntry(1,[255,128,0,0])
m = c.SetColorEntry(65535,[0,128,255,255])
c.CreateColorRamp(1,n,65535,m)
band.SetColorTable(c)

I discovered that the 64K colors are due to the UInt16 (tested GDT_Byte and got 255) so i realized that maybe i need to create a ramp?

But the above code fails with:

Traceback (most recent call last):
  File "makecolortable.py", line 14, in <module>
    n = c.SetColorEntry(1,[255,128,0,0])
  File "/usr/lib/python2.7/dist-packages/osgeo/gdal.py", line 1113, in SetColorEntry
    return _gdal.ColorTable_SetColorEntry(self, *args)
TypeError: Invalid values in ColorEntry sequence 

That sequence appears correct as all four values meet the short requirement, (i think this is the code that produces the error):

if ( !PyArg_ParseTuple( $input,"hhh|h", &ce.c1, &ce.c2, &ce.c3, &ce.c4 ) ) {
  PyErr_SetString(PyExc_TypeError, "Invalid values in ColorEntry sequence ");


--nix

On Mar 8, 2013, at 16:35, Robert Nix <robert at urban4m.com> wrote:

> Hi,
> 
> I'm trying to add a color table to a 1-band UInt16 GeoTiff with Python as follows:
> 
> import numpy as np
> import gdal
> 
> driver = gdal.GetDriverByName('GTiff')
> dst_ds = driver.Create('testcolor.tif', 100, 100, 1, gdal.GDT_UInt16)
> 
> band = dst_ds.GetRasterBand(1)
> band.SetRasterColorInterpretation(gdal.GCI_PaletteIndex)
> 
> c = gdal.ColorTable(gdal.GCI_PaletteIndex)
> c.SetColorEntry(1,(255,127,0,63))
> band.SetColorTable(c)
> 
> a = np.random.randint(1,10,size=(100,100))
> band.WriteArray(a)
> 
> dst_ds = None
> 
> The problem is that when i run gdalinfo on the testcolor.tif, it lists 65535 color table entries:
> 
> Driver: GTiff/GeoTIFF
> Files: testcolor.tif
>        testcolor.tif.aux.xml
> Size is 100, 100
> Coordinate System is `'
> Image Structure Metadata:
>   INTERLEAVE=BAND
> Corner Coordinates:
> Upper Left  (    0.0,    0.0)
> Lower Left  (    0.0,  100.0)
> Upper Right (  100.0,    0.0)
> Lower Right (  100.0,  100.0)
> Center      (   50.0,   50.0)
> Band 1 Block=100x40 Type=UInt16, ColorInterp=Palette
>   Color Table (RGB with 65536 entries)
>     0: 1,0,0,255
>     1: 1,0,0,255
>     2: 0,0,0,255
>     3: 0,0,0,255
> ...
>   65533: 0,0,0,255
>   65534: 0,0,0,255
>   65535: 0,0,0,255
> 
> What's going on … besides the fact that maybe i'm not understanding color-tables? If it's clear i don't understand, is there a good resource for understanding color-tables? Or must I go learn the source code (which i really don't have to do)?
> 
> Thanks
> --nix
> 

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