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R8218/private/rleDecoder.m
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rleDecoder.m
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function [decodedData, decodedBytes] = rleDecoder(encodedData, ...
scanlineWidth)
%rleDecoder Decompress data using HDR adaptive run-length encoding.
% [decodedData, decodedBytes] = rleCoder(encodedData, scanlineWidth)
% decompresses the RLE-compressed values in encodedData and places the
% result in decodedData. At most scanlineWidth values are decoded,
% and decodedBytes contains the number of values in encodedData that
% were used during decompression.
% Copyright 2007-2013 The MathWorks, Inc.
% Unlike the description in Graphics Gems II.8 (p.89), code values greater
% than 128 correspond to repeated runs, while smaller code values are
% literal dumps. See the following web site for more details:
% <http://www.andrew.cmu.edu/user/yihuang/radiance_pic/rgbe.html#syntax>.
% The adaptive RLE used by HDR also does not shift code values by one.
if (isempty(encodedData) || (scanlineWidth == 0))
decodedData = [];
decodedBytes = 0;
return
end
% Create a temporary buffer for the decoded data.
decodedData = zeros(1, scanlineWidth, class(encodedData));
% Loop over the compressed data until this part of the scanline is full.
inputPtr = 1;
outputPtr = 1;
while (outputPtr <= scanlineWidth)
if (encodedData(inputPtr) > 128)
% A run of the same value.
runLength = double(encodedData(inputPtr)) - 128;
if ((runLength - 1) > (scanlineWidth - outputPtr))
warning(message('images:rleDecoder:badRunLength'));
end
decodedData(outputPtr:(outputPtr + runLength - 1)) = ...
encodedData(inputPtr + 1);
inputPtr = inputPtr + 2;
outputPtr = outputPtr + runLength;
else
% A run of literal data.
runLength = double(encodedData(inputPtr));
inputPtr = inputPtr + 1;
if ((runLength == 0) || ...
((runLength - 1) > (scanlineWidth - outputPtr)))
warning(message('images:rleDecoder:badRunLength'));
end
if ((inputPtr + runLength - 1) > numel(encodedData))
error(message('images:rleDecoder:notEnoughEncodedData'))
end
decodedData(outputPtr:(outputPtr + runLength - 1)) = ...
encodedData(inputPtr:(inputPtr + runLength - 1));
inputPtr = inputPtr + runLength;
outputPtr = outputPtr + runLength;
end
end
decodedBytes = inputPtr - 1;
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