[GRASS-user] Landsat 8 Color Matching

[Michele Toma]

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.

-Michele

-----Original Message-----
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

Michele Toma:

>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 
>grayscale images?

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 
>using?
>
>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.

Nikos

>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'