[gdal-dev] How to decrease file size of colored raster bands?

[afernandez]

Hi Scott,
As I mentioned to Laurentiu, I'm still not getting the handle on how to use 
overviews but will keep working at it. However, this is only useful to me 
(and probably to other people) if they can be used from a python script, 
not from the OS.
Thanks,
Arturo
Scott wrote:
As a test you can skip the whole python debacle and try this:
gdal_translate -f COG -co COMPRESS=DEFLATE -scale 0 255 -ot Byte source.tif 
target.tif
On 6/1/23 07:35, afernandez wrote:
Hello,
I'm generating a raster file with GDAL. The pseudo-code (where the > raster 
is loaded as 'var') for the colored version reads:
# Initial manipulations
dims = var.dimensions
shape = var.shape
driver_name = 'GTIFF'
driver = gdal.GetDriverByName(driver_name)
np_dtype = var.dtype
type_code = gdal_array.NumericTypeCodeToGDALTypeCode(np_dtype)
gdal_ds = driver.Create(_my_path_, cols, rows, 1, > gdal.GDT_UInt16)
gdal_ds.SetProjection(_my_projection_)
gdal_ds.SetGeoTransform(_my_transformation_)
# Creation of the bands and scaled matrix
band = gdal_ds.GetRasterBand(1)
data = var[_chosen_index_]
data = ma.getdata(data)
data_scaled = np.interp(data, (data.min(), data.max()), (0, > 255))
data_scaled2 = data_scaled.astype(int) # This is to rescale > into integers 
so that it can color the layer
# *** Lines to set up the color palette ***
# Write the array to band once everything has been rescaled
band.WriteArray(data_scaled2)
gdal_ds.FlushCache()
This works well but the problem is that the generated file becomes too > 
large and difficult to work with. If I change to a black and white > 
representation by simply changing the 7th line to:
gdal_ds = driver.Create(out_path, cols, rows, 1, type_code)
The new file has a size smaller than 1% of the colored one. I was > 
wondering if there is anything intermediate (with colors but generating > a 
smaller size) or if I would need a more radical approach such as using > a 
driver different from GTIFF or something else.
Thanks.
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