[GRASS-user] Landsat 8 Color Matching
michele.toma at airborne.aero
Thu Aug 18 11:45:49 PDT 2016
Hi Nikos, everyone,
Is the any more information documented about how the i.histo.match tool works? I am unsure if I have entered the correct information to run the tool properly and there is not much information on the documentation page. I ran the tool against all bands in two different images which seemed to work fine (no errors), but when creating an RGB layer of one of the images, it displayed a solid pink image. Displaying an RGB using the bands created before the histogram matching seems to be fine.
From: Nikos Alexandris [mailto:nik at nikosalexandris.net]
Sent: Tuesday, August 16, 2016 3:22 AM
To: Michele Toma
Cc: grass-user at lists.osgeo.org
Subject: Re: [GRASS-user] Landsat 8 Color Matching
>I have multiple Landsat 8 scenes taken on the same day/same path, but
>they vary in brightness. I believe this to be caused by the time of day
>that the image was taken as the northern image is brighter (taken
>earlier in the day) and the southern image is darker (taken later in
>the day). This has occurred for multiple images. Is there a way to make
>the colors match between tiles?
>I've attempted to use i.histo.match on my composite rgb images which
>resulted in distorted colors. Should this tool only be used on
You would want to perform histogram matching after the conversion to radiance/reflectance and before composing an RGB image.
>Are there other GRASS tools I am not aware of that I should be using?
>Is the color distortion caused by any of the other tools that I am
>Below are the steps that I've taken to process my images:
>1. Import all Landsat 8 bands to GRASS 7.0.4
>2. Convert DN to reflectance
>a. i.landsat.toar input=LC81100362016082LGN00_B output=LC81100362016082LGN00_refl metfile=LC81100362016082LGN00_MTL.txt
>3. Pansharpen using i.fusion.hpf
>a. i.fusion.hpf pan=LC81100362016082LGN00_relf8 msx=LC81100362016082LGN00_refl4, LC81100362016082LGN00_relf3, LC81100362016082LGN00_refl2 suffix=hpf
>4. Histogram equalization
>a. r.colors -e map=LC81100362016082LGN00_refl4.hpf color=grey
Note, this merely retouched the "color-table" and not the data itself.
>5. Color balance using i.colors.enhance
>a. i.colors.enhance red=LC81100362016082LGN00_refl4.hpf green=LC81100362016082LGN00_refl3.hpf blue=LC81100362016082LGN00_refl2.hpf
>6. Set region
>a. g.region raster=LC81100362016082LGN00_refl2.hpf
>7. Create RGB composite
>a. r.composite red=LC81100362016082LGN00_refl4.hpf green=LC81100362016082LGN00_refl3.hpf blue=LC81100362016082LGN00_refl2.hpf output=LC81100362016082LGN00_refl_rgb
>8. Export image
>a. r.out.gdal input= LC81100362016082LGN00_refl_rgb output= LC81100362016082LGN00.tif format='GTiff'
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