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nitfReadJPEG.m
853593394513aterrier-plotUpdate

nitfReadJPEG.m
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			function X = nitfReadJPEG(details, region)
			%nitfReadJPEG Extract JPEG-compressed image from NITF file.
			% X = nitfReadJPEG(DETAILS, REGION) returns the image X from the NITF
			% file described in the DETAILS structure. The REGION argument is
			% currently not used.
			%
			% See MIL-STD-188-198 for details of this scheme.

			% Copyright 2010-2013 The MathWorks, Inc.

			% Currently there's no pixel subsetting for NITF I/O.
			if (~isempty(region))
			error(message('images:nitfread:jpegSubsetting'))
			end

			% Get the JPEG data from the file.
			compData = getJpegStream(details);

			% Get the number of blocks, dimensions and markers.
			nColsBlocks = double(swapbytes(typecast(compData(15:16), 'uint16')));
			nRowsBlocks = double(swapbytes(typecast(compData(17:18), 'uint16')));

			h = details.tileHeight;
			w = details.tileWidth;

			[startIdx, stopIdx, maskedBlocks] = getBlockLocations(compData, details, nColsBlocks, nRowsBlocks);

			% Create the full-sized image.
			X = createOutputArray(details);

			% Read all of the blocks.
			name = [tempname '.jpg'];
			cleaner = onCleanup(@() delete(name));

			idx = 1;
			r = 1;
			for j = 1:nRowsBlocks
			c = 1;
			for i = 1:nColsBlocks

			% If the block is masked, update the position and go to the next.
			if (maskedBlocks(idx))
			c = c + w;
			idx = idx + 1;
			continue;
			end

			start = startIdx(idx);
			stop = stopIdx(idx);
			frameData = compData(start:stop);

			% Read the portion of the image and store it.
			data = getImageDataFromFrame(name, frameData);
			X(r:(r+h-1), c:(c+w-1), :) = data;

			% Update the position.
			c = c + w;
			idx = idx + 1;
			end

			r = r + h;
			end



			function compData = getJpegStream(details)

			% Open the NITF file.
			fid = fopen(details.filename, 'rb');
			if (fid == 0)
			error(message('images:nitfread:jpegFileOpen', details.filename))
			else
			c = onCleanup(@() fclose(fid));
			end

			% Move to the location in the file where the JPEG stream begins.
			details.offsetStart = convertOffsetType(details.offsetStart);

			status = fseek(fid, details.offsetStart, 'bof');
			if (status ~= 0)
			error(message('images:nitfread:jpegFseek'));
			end

			% Read the JPEG data, which comprises the rest of the NITF file.
			compData = fread(fid, inf, 'uint8=>uint8');

			% Trim leading 0xFF pad values before SOI.
			while ((numel(compData > 2)) && (compData(2) == 255))
			compData(1) = [];
			end

			% Validate the JPEG stream. It should start with an SOI marker (0xFF 0xD8)
			% and then an APP6 marker (0xFF 0xE6).
			if (~isequal(compData(1:2), [255; 216]))
			error(message('images:nitfread:badEncapsulation'))
			end

			if (~isequal(compData(3:4), [255; 230]))
			error(message('images:nitfread:missingAppMarker'))
			end



			function [startIdx, stopIdx, skipIdx] = getBlockLocations(compData, details, nColsBlocks, nRowsBlocks)

			% Find the Image markers
			SOIidx = findpattern(compData', sscanf('ff d8', '%x')');
			EOIidx = findpattern(compData', sscanf('ff d9', '%x')');
			SOFidx = sort([findpattern(compData', sscanf('ff c0', '%x')'), ...
			findpattern(compData', sscanf('ff c1', '%x')'), ...
			findpattern(compData', sscanf('ff c2', '%x')'), ...
			findpattern(compData', sscanf('ff c3', '%x')')]);

			if ((numel(SOIidx) ~= numel(EOIidx)) \|\| ...
			(numel(SOIidx) ~= numel(SOFidx)))
			error(message('images:nitfread:jpegSoiEoiCount'))
			end

			% Does the NITF file use block masking, where some tiles are "virtual"?
			if (isfield(details, 'blockOffsets'))
			blockMasking = true;
			skipIdx = (details.blockOffsets == intmax('uint32'));
			else
			blockMasking = false;
			skipIdx = false(nRowsBlocks * nColsBlocks, 1);
			end

			if ((numel(SOIidx) ~= (nColsBlocks * nRowsBlocks)) && ~blockMasking)
			warning(message('images:nitfread:wrongSOFIndexCount'));
			end

			% Compute where each tile's JPEG data starts and ends.
			if (~blockMasking)
			% If there's no masking, the data starts and stops with each SOI/EOI pair.
			startIdx = SOIidx;
			stopIdx = EOIidx + 1;
			else
			% If there is masking, the data start positions are given by the
			% blockOffset values. NaN indicates a masked out frame.
			startIdx = details.blockOffsets + 1;
			startIdx(skipIdx) = NaN;

			% Each tile ends directly before the next one starts. (Masked frames
			% are tricky, so just use the end of the stream.) Shift the start
			% values one over and subtract one to determine where they end. The
			% last stop value is the last compressed value location.
			stopIdx = [(startIdx(2:end) - 1) numel(compData)];
			stopIdx(isnan(stopIdx)) = numel(compData);
			stopIdx(skipIdx) = NaN;
			end



			function X = createOutputArray(details)

			imgSize = [details.imageHeight, details.imageWidth, details.samplesPerPixel];
			if (details.bitsPerSample <= 8)
			X = zeros(imgSize, 'uint8');
			elseif (details.bitsPerSample <= 16)
			X = zeros(imgSize, 'uint16');
			else
			error(message('images:nitfread:jpegBitDepth', details.bitsPerSample));
			end



			function img = getImageDataFromFrame(name, frameData)

			fid = fopen(name, 'wb');
			if (fid == 0)
			error(message('images:nitfread:tmpJpegFileOpen', name))
			else
			c = onCleanup(@() fclose(fid));
			end

			fwrite(fid, frameData, 'uint8');
			delete(c);

			img = imread(name, 'jpeg');



			function idx = findpattern(array, pattern)
			%FINDPATTERN Find a pattern in an array.

			% Despite its name, "strfind" is very good at finding numeric patterns in
			% numeric vectors.
			idx = strfind(array, pattern);


			function out = convertOffsetType(in)

			if (in > intmax('uint32'))
			error(message('images:nitfread:offsetTooBigForJPEG'))
			end

			out = double(in);

R8218/private/nitfReadJPEG.m853593394513aterrier-plotUpdate

nitfReadJPEG.mView Options

R8218/private/nitfReadJPEG.m
853593394513aterrier-plotUpdate

nitfReadJPEG.m
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