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R8218/private/dicom_encode_jpeg_lossy.m
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dicom_encode_jpeg_lossy.m
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function [fragments, frames] = dicom_encode_jpeg_lossy(X, bits)
%DICOM_ENCODE_JPEG_LOSSY Encode pixel cells using lossy JPEG compression.
% [FRAGMENTS, LIST] = DICOM_ENCODE_JPEG_LOSSY(X) compresses and encodes
% the image X using baseline lossy JPEG compression. FRAGMENTS is a
% cell array containing the encoded frames (as UINT8 data) from the
% compressor. LIST is a vector of indices to the first fragment of
% each compressed frame of a multiframe image.
%
% See also DICOM_ENCODE_RLE, DICOM_ENCODE_JPEG_LOSSLESS.
% Copyright 1993-2011 The MathWorks, Inc.
% Because lossy JPEG compression of signed data doesn't make sense,
% error. See PS 3.5 Sec. 8.2.1.
X = convertSigned(X);
% Use IMWRITE to create a JPEG image, but don't warn about signed data.
numFrames = size(X,4);
fragments = cell(numFrames, 1);
frames = 1:numFrames;
% The maximum bit-depth for lossy JPEG is 12 bits/sample.
if (bits > 12)
bits = 12;
end
if (max(X(:)) >= 4096)
warning(message('images:dicom_encode_jpeg_lossy:sampleTooLarge', sprintf( '%ld', max( X( : ) ) )))
end
% Write each frame.
for p = 1:numFrames
tempfile = tempname;
imwrite(X(:,:,:,p), tempfile, 'jpeg', 'bitdepth', bits);
% Read the image from the temporary file.
fid = fopen(tempfile, 'r');
fragments{p} = fread(fid, inf, 'uint8=>uint8');
fclose(fid);
% Remove the temporary file.
try
delete(tempfile)
catch %#ok<CTCH>
warning(message('images:dicom_encode_jpeg_lossy:tempFileDelete', tempfile));
end
end
function X = convertSigned(X)
% Image has signed data.
if (~isConvertible(X))
error(message('images:dicom_encode_jpeg_lossy:signedData'))
end
switch (class(X))
case 'int8'
X = uint8(X);
case 'int16'
X = uint16(X);
case 'int32'
X = uint32(X);
case 'int64'
X = uint8(X);
otherwise
% No op.
end
function tf = isConvertible(X)
%We can silently convert any type where all of the values are nonnegative.
tf = ~(any(X(:) < 0));
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