Numpy processing in OTB Applications

Input and output images to any OTB application in the form of numpy array is now possible in OTB python wrapping. The python wrapping only exposes OTB ApplicationEngine module which allow to access existing C++ applications. Due to blissful nature of ApplicationEngine’s loading mechanism no specific wrapping is required for each application.

Numpy extenstion to Python wrapping allows data exchange to application as an array rather than a disk file. Ofcourse, it is possible to load an image from file and then convert to numpy array or just provide a file as earlier via Application.SetParameterString(...).

This brige that completes numpy and OTB makes it easy to plug OTB into any image processing chain via python code that uses GIS/Image processing tools such as GDAL, GRASS GIS, OSSIM that can deal with numpy.

Below code reads an input image using python pillow (PIL) and convert it to numpy array. This numpy array is used an input to the application set SetImageFromNumpyArray(...) method. The application used in this example is ExtractROI. After extracting a small area the ouput image is taken as numpy array with GetImageFromNumpyArray(...) method

import sys
import os
import numpy as np
import otbApplication
from PIL import Image as PILImage

pilimage = PILImage.open('poupees.jpg')
npimage = np.asarray(pilimage)
inshow(pilimage)

ExtractROI = otbApplication.Registry.CreateApplication('ExtractROI')
ExtractROI.SetImageFromNumpyArray('in', npimage)
ExtractROI.SetParameterInt('startx', 140)
ExtractROI.SetParameterInt('starty', 120)
ExtractROI.SetParameterInt('sizex', 150)
ExtractROI.SetParameterInt('sizey', 150)
ExtractROI.Execute()

ExtractOutput = ExtractROI.GetImageAsNumpyArray('out')
output_pil_image = PILImage.fromarray(np.uint8(ExtractOutput))
imshow(output_pil_image)