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Saving rasters which are extracted by mask using python will change the results and generate some abnormal values

Question asked by LiXu1994 on Oct 12, 2019
Latest reply on Oct 13, 2019 by Dan_Patterson


I am trying to extract the rasters by mask in batches using Python in ArcGIS 10.3. When I extracted one sample raster data by mask using the Extract by Mask tool in ArcToolbox, the result is what I expected. But I have too much raster data to extracted one by one, so I used this code to achieve it:

import arcpy
from arcpy import env
from import *

#environment settings
env.workspace = "E:/MGH_data/MGH_newLandsat/Bulk Order 1043142/NDVI_TIFF"
rasterList = arcpy.ListRasters("*","tif")

#out put path
output_path = "E:/MGH_data/MGH_newLandsat/Bulk Order 1043142/NDVI_Clip/"

#mask shapfile
inMaskData = "F:/MsAcademicPaper/MaGuiHe_HJL/MGH_huangjingling/basin_area.shp"

for raster in rasterList:
     print raster
     inRaster = raster
# Execute ExtractByMask
     outExtractByMask = ExtractByMask(inRaster, inMaskData)
# Save the output
     outname = output_path + inRaster


when I execute the above commands in Python window,  there are some abnormal values in the nodata area in the results. Here is the value range of the result with abnormal values (the low value)


So I was wondering which step is wrong. So I tried to use this code to extract one sample raster data, and I just ran the code only before saving the output, which means it will not to execute the code that is used to save the output (the last two lines of the code), and the result is correct, without any abnormal values. Here is the value range of the correct raster result:


So I guess the problem is from the Save output raster step. But I checked the code many times and still have no idea to solve it. Anybody knows what's going wrong? I do appreciate your help.