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R8218/CT/private/dicom_compress_pixel_cells.m
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dicom_compress_pixel_cells.m
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function attrs = dicom_compress_pixel_cells(pixel_cells, txfr, bits_allocated, dims)
%DICOM_COMPRESS_PIXEL_CELLS Compress pixel cells into fragments.
% ATTRS = DICOM_COMPRESS_PIXEL_CELLS(CELLS, TXFR, BITS, DIMS) compress
% the pixel cells CELLS using the transfer syntax TXFR. BITS is the
% size of each pixel cell, and DIMS is the MATLAB dimensions of the
% data contained in the pixel cells.
%
% The result is a structure of attributes containing the compressed
% pixel cell fragments and item delimiters.
%
% See also DICOM_ADD_ITEM.
% Copyright 1993-2010 The MathWorks, Inc.
% Encapsulated (compressed) pixel cells have the following structure:
%
% (7FE0,0010) with undefined length (handled elsewhere)
% (FFFE,0000) containing off-set table or 0 length data
% (FFFE,0000) for each fragment (a collection of UINT8 data)
% (FFFE,00DD) with 0 length data
% Create an empty container for the "sequence."
attrs = struct([]);
% Compress the pixel_cells.
[fragments, frames] = compress_cells(pixel_cells, txfr, bits_allocated, dims);
% Create the Basic Offset Table.
offsets = build_offset_table(fragments, frames);
attrs = dicom_add_item(attrs, 'FFFE', 'E000', offsets);
% Add the fragments.
for p = 1:length(fragments)
attrs = dicom_add_item(attrs, 'FFFE', 'E000', fragments{p});
end
% Add the sequence delimiter.
attrs = dicom_add_item(attrs, 'FFFE', 'E0DD');
function [fragments, frames] = compress_cells(pixel_cells, txfr, ...
bits_allocated, dims)
%COMPRESS_CELLS Return a cell array of encoded pixel cell fragments.
switch (txfr)
case '1.2.840.10008.1.2.5'
[fragments, frames] = dicom_encode_rle(pixel_cells, bits_allocated, dims);
fragments = padFragments(fragments);
case '1.2.840.10008.1.2.4.50'
[fragments, frames] = dicom_encode_jpeg_lossy(pixel_cells, bits_allocated);
fragments = padFragments(fragments);
case '1.2.840.10008.1.2.4.70'
[fragments, frames] = dicom_encode_jpeg_lossless(pixel_cells, bits_allocated);
fragments = padFragments(fragments);
case '1.2.840.10008.1.2.4.90'
[fragments, frames] = dicom_encode_jpeg2000_lossless(pixel_cells, bits_allocated);
fragments = padFragments(fragments);
case '1.2.840.10008.1.2.4.91'
[fragments, frames] = dicom_encode_jpeg2000_lossy(pixel_cells, bits_allocated);
fragments = padFragments(fragments);
otherwise
error(message('images:dicom_compress_pixel_cells:cannotCompress', txfr))
end
function offset_table = build_offset_table(fragments, frames)
%BUILD_OFFSET_TABLE Create a vector of offsets to the start of the frames.
% Don't store an offset table for just one frame.
if (length(frames) == 1)
offset_table = uint32([]);
return
end
% Build an offset table, a UINT32 vector with byte offsets to the
% beginning of the next frame. The offsets are relative to the end of
% the offset table item, which is always followed by the first fragment.
offset_table = repmat(uint32(0), size(frames));
current_offset = 0;
current_frame = 1;
for p = 1:length(fragments)
if (p == frames(current_frame))
% Beginning of frame starts at current position.
offset_table(current_frame) = current_offset;
current_frame = current_frame + 1;
% Offset to next fragment is 8 bytes for tag and length plus size
% of fragment.
current_offset = current_offset + 8 + numel(fragments{p});
else
% Not the beginning of a new frame.
current_offset = current_offset + 8 + numel(fragments{p});
end
end
function fragments = padFragments(fragments)
%padFragments Add null bytes to odd-length fragments.
for p = 1:numel(fragments)
if (rem(numel(fragments{p}), 2) == 1)
fragments{p}(end+1) = 0;
end
end
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