Cut raster by pixels in GDAL

Question

i've some georeferenced images that have the size of 1280 X 960. I need to cut the outer pixels to have a size of 1220 X 900 (i need to cut 30 pixel for each borders).

Can i do this using GDAL or a python script using numpy array?

I try using Gdal warp: gdalwarp -to SRC_METHOD=NO_GEOTRANSFORM -te 30 30 1250 930 input.tif output.tif

But in this case the result is a not georeferenced image.

Answer 1

Gdal_translate can do that with -srcwin https://gdal.org/programs/gdal_translate.html.

-srcwin Selects a subwindow from the source image for copying based on pixel/line location.

The minimal command would be

gdal_translate -srcwin 30 30 1220 900 input.tif output.tif

Instead of using gdal_translate binary you can use it also as a library in Python https://trac.osgeo.org/gdal/wiki/rfc59.1_utilities_as_a_library.

The order of terms is

• offset from the top-left corner in x-direction (width)
• offset from the top-left corner in y-direction (height)
• size of the output image in x-direction
• size of the output image in y-direction

Answer 2

In documentation for gdalwarp command:

https://gdal.org/programs/gdalwarp.html

there is an example where is pointed out that options in your command are precisely used for un-georeferenced images and it is also necessary a cutline as csv file. So, for georeferenced images, you only need to add or to rest 30*(Pixel Size) to xmin ymin xmax ymax values. These values can easily get in Raster Properties -> Information -> Extent, Pizel Size.

To test my approach, I created a random raster with a dimension of 1280x960; whose values for extent and Pixel Size were as follows:

Extent: 354971.3488602247089148,4378722.8366580698639154 : 426000.5231592403142713,4473428.4023900907486677

Pizel Size: 73.98872322814125368

For new cut raster:

xmin + 30*(Pixel Size): 354971.3488602247089148 + 2219.661696844 = 357191.010557069
ymin + 30*(Pixel Size): 4378722.8366580698639154 + 2219.661696844 = 4380942.498354914
xmax - 30*(Pixel Size): 426000.5231592403142713 - 2219.661696844 = 423780.861462396
ymax - 30*(Pixel Size): 4473428.4023900907486677 - 2219.661696844 = 4471208.740693247

So, my complete command is:

gdalwarp -overwrite -te 357191,010557069 4380942,498354914 423780,861462396 4471208,740693247 random.tif out.tif

When I ran in Console above command, I got following result:

zeito@zeito-pc:~/pyqgis_data$ gdalwarp -overwrite -te 357191,010557069 4380942,498354914 423780,861462396 4471208,740693247 random.tif out.tif
Creating output file that is 900P x 1220L.
Processing random.tif [1/1] : 0...10...20...30...40...50...60...70...80...90...100 - done.

where it can be observed that raster dimension is as expected: 900P x 1220L.

In the following image are the original and the resulting raster. Resulting raster (with pseudocolor symbology for better identification) was effectively cut 30 pixels for each border.