On Mon, 22 Apr 2024, Raley, Nathan via gdal-dev wrote:
Hmm, good catch. Looking at the stats for the red band:
Band 1 Block=128x128 Type=UInt16, ColorInterp=Gray
Min=130.000 Max=36265.000
Minimum=130.000, Maximum=36265.000, Mean=10415.962, StdDev=3502.933
NoData Value=0
Metadata:
STATISTICS_MAXIMUM=36265
STATISTICS_MEAN=10415.961859513
STATISTICS_MINIMUM=130
STATISTICS_STDDEV=3502.9325925887
STATISTICS_VALID_PERCENT=49
So, is there no way to actually do this via command line, or am I going to have
to write a python lib to actually read through these and determine what they
should be scaled to?
There is gdal_transform -scale (and -scale_2 etc.)
What are you going to do with the resulting file ?
QGIS allows you to make these sorts of adjustments at view-time.
Remember that the max and min values present in an image may not represent
the full range and the next-door image may have a larger or smaller range
(or just a shifted range). Imagine a row of three tiles; the middle on on
the edge of a glacier, the first entirely on the glacier and the last
entirely off the glacier. You may wish to apply the same scaling to all
three.
From: Daniel Evans <daniel.fred.ev...@gmail.com>
Sent: Monday, April 22, 2024 9:29 AM
To: Raley, Nathan <nra...@gaig.com>
Cc: 'gdal-dev@lists.osgeo.org' (gdal-dev@lists.osgeo.org)
<gdal-dev@lists.osgeo.org>
Subject: [External] Re: [gdal-dev] Question on building multi band composite
and going back to RGB GeoTiff
Hi Nathan, My initial suspicion might just be that the scaling the data
provider did to go from the raw data to a human-eye-friendly RGB composite
isn't the conversion you're assuming. I know that with the data I regularly
work with,
Hi Nathan,
My initial suspicion might just be that the scaling the data provider did to go
from the raw data to a human-eye-friendly RGB composite isn't the conversion
you're assuming.
I know that with the data I regularly work with, it may be provided as Uint16,
but the data range doesn't extend all the way to 65535.
If you compare the values in the separate R and G images to the RGB composite,
do they appear to match the conversion you're assuming, or is there a different
scaling (and possibly offset)?
Cheers,
Daniel
On Mon, 22 Apr 2024, 15:20 Raley, Nathan via gdal-dev,
<gdal-dev@lists.osgeo.org<mailto:gdal-dev@lists.osgeo.org>> wrote:
I currently have a RGB geotiff composite image that has a Byte datatype. I
also have individual band images for R, G, Redge, and NIR that are UInt16
datatypes. Since I’m missing the Blue band from the individual bands, I was
attempting to extract the blue band from the RGB composite image, scale it up
to the UInt16 datatype, and build a composite VRT with R, G, B, NIR, RE bands
included in it. I was then attempting to extract the RGB bands from the
multispec VRT in order to see if the process was working as intended, but I’m
getting an extremely blue image.
Can anyone shed some light as to what I may be doing wrong here?
I started by building a VRT for each band:
gdal_translate source_RGB.tif b.vrt -ot UInt16 -of VRT -b 3 -scale 0 255 0 65535
gdalbuildvrt -b 1 r.vrt source_R.tif
gdalbuildvrt -b 1 g.vrt source_G.tif
gdalbuildvrt -b 1 nir.vrt source_NIR.tif
gdalbuildvrt -b 1 re.vrt source_RE.tif
I then merged the VRTs:
gdalbuildvrt -separate multispec.vrt r.vrt g.vrt b.vrt nir.vrt re.vrt
I now have a multispec.vrt with the R, G, B, NIR, and RE bands, all with a
UInt16 datatype.
Now, I attempted to rebuild a RGB GeoTiff from the composite VRT with something
like:
gdal_translate -ot Byte -of GTiff -b 1 -b 2 -b 3 -scale 0 65535 0 255 -co
PHOTOMETRIC=RGB multispec.vrt multispec.tif
Viewing the result in QGIS appears overly blue. What am I doing wrong here?
Thanks,
Nathan
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