topic Replace values in RGB rasters in Python Questions

Replace values in RGB rasters

bogdanpalade1 — Mon, 01 Jul 2013 10:06:27 GMT

Hello,

My goal is to replace the values of one raster (of all the 3 RGB bands) with the values of another raster (also 3 bands) where the values of the initial raster meet some requirements, for example only where Band_1 (Red) = 205, Band_2 (Green) = 255 and Band_3 (Blue) = 194. The code bellow does not work saying something like the raster 205 is not supported...I also dont know how to loop through the RGB arrays...

Initially I tried to do this in raster calculator but did not figure it out how to do it...
Here I put the code where I want to replace the values of the Image17 with the values of Image16:

import arcpy, os
arcpy.CheckOutExtension("Spatial")

arcpy.env.workspace = r"Z:\BP\TST"
Image16 = r"Z:\BP\TST\16.tif"
Image17 = r"Z:\BP\TST\17.tif"

Image16_red = arcpy.sa.Raster(Image16+"\\Band_1")
Image16_green = arcpy.sa.Raster(Image16+"\\Band_2")
Image16_blue = arcpy.sa.Raster(Image16+"\\Band_3")


Image17_red = arcpy.sa.Raster(Image17+"\\Band_1")
Image17_green = arcpy.sa.Raster(Image17+"\\Band_2")
Image17_blue = arcpy.sa.Raster(Image17+"\\Band_3")

if Image17_red == "205":
    if Image17_green == "255":
        if Image17_blue == "194":
            output_obj = (Image17_red = Image16_red) & (Image17_green = Image16_green) & (Image17_blue = Image16_blue)
            output_obj.save(r"Z:\BP\TST\output.tif")

Could you please give me a hint on how to solve this?

Thank you very much

Re: Replace values in RGB rasters

markdenil — Mon, 01 Jul 2013 12:15:04 GMT

If you use Copy Raster or raster To Other Formats to save your three band composite image as a GRID Stack,
you will then have access to the three component GRIDs (one for each band).

If you run the Reclassify on the GRID (band) you want to change,
and then use Composite Bands to reassemble the composite from the GRIDs,
you should accomplish what you want to do.

In short:
1. disassemble
2. adjust
3. reassemble

Re: Replace values in RGB rasters

bogdanpalade1 — Mon, 01 Jul 2013 15:10:55 GMT

Thank you very much for your reply. Meanwhile it took like 5 minutes to solve it with erdas model maker :). No need to separate and layer stack after...