How do I work with large NITF (National Imagery Transmission Format) files?

I see that nitfread has a PixelRegion option to read part of an image, and I know about the blockedImage infrastructure to process large images. How do I use them together?

Answer 1

[Ashish Uthama]

The blockedImage infrastructure allows for 'custom adapters' to connect arbitrary data sources into the blockedImage framework for processing large images.

%% Process Large NITF SAR Imagery with blockedImage
% Download a 197 MB SICD (complex SAR) file from NGA's public sample set:
%   websave("sicd_HH.nitf", "https://six-library-github-public.s3.us-east-2.amazonaws.com/sicd_example_1_PFA_RE32F_IM32F_HH.nitf")
% Open as a blockedImage using the NITF adapter (no full load into memory)
bim = blockedImage("sicd_HH.nitf", Adapter=NITFAdapter);
% Compute SAR magnitude (dB) block-by-block — works on arbitrarily large files
% Can be parallelized across a cluster with UseParallel=true
bMag = apply(bim,...
    @(bs) 20*log10(abs(complex(bs.Data(:,:,1), bs.Data(:,:,2))) + 1));
% Visualize with dynamic range scaling
imageshow(bMag, DisplayRange=[30 80], Colormap=hot(256));
title("SAR Magnitude (dB) — " + bim.Size(1) + "×" + bim.Size(2) + " pixels");

Note: this adapter was created using the matlab-process-large-images skill! You can use this skill to further customize this adapter to suit your specific processing needs.