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% read_rle_rgbe
%
% Written by Lawrence A. Taplin (taplin@cis.rit.edu)
%
% Based loosely on the c-code RGBE implementation written by Bruce Walters
% http://www.graphics.cornell.edu/~bjw/rgbe.html
%
% function to read a run length encoded RGBE picture file and header. This
% does not work if the image is not RLE!!!
%
% Note to Psychtoolbox users: Please use the higher level HDRRead.m routine
% for better generality in your code. This routine is used as helper for
% HDRRead.
%
function [img, fileinfo] = read_rle_rgbe(filename)
%open the file
fid = fopen(filename,'r');
%read the magic number
tline = fgetl(fid);
if length(tline) < 3 || ~strcmp(tline(1:2), '#?')
error('invalid header');
end
fileinfo.identifier = tline(3:end);
%read the header variables into a structure
tline = fgetl(fid);
while ~isempty(tline)
%find and set the variable name
n = strfind(tline,'=');
if ~isempty(n) % skip stuff I don't understand
vname = lower(tline(1:n(1)-1));
vval = tline(n+1:end);
fileinfo = setfield(fileinfo,vname,vval); %#ok<SFLD>
%fprintf('Variable = %s, Value = %s\n',vname, vval);
end
%read the next line
tline = fgetl(fid);
end
%set the resolution variables
tline = fgetl(fid);
fileinfo.Ysign = tline(1);
[fileinfo.height,~,~,nextindex] = sscanf(tline(4:end),'%d',1);
fileinfo.Xsign = tline(nextindex+4);
[fileinfo.width] = sscanf(tline(nextindex+7:end),'%d',1);
%fprintf('resolution: %s\n',tline);
%allocate space for the scan line data
img = zeros(fileinfo.height, fileinfo.width, 3);
%read the scanline data
if strcmp(fileinfo.format, '32-bit_rle_rgbe')
%fprintf('Decoding RLE Data stream\n');
end
%read the remaining data
data = fread(fid,inf,'uint8');
fclose(fid);
scanline_width = fileinfo.width;
num_scanlines = fileinfo.height;
if ((scanline_width < 8) || (scanline_width > 32767))
% run length encoding is not allowed so read flat
img = rgbe2float(reshape(data,fileinfo.width,fileinfo.height,4));
return;
end
scanline_buffer = repmat(uint8(0),scanline_width,4);
dp = 1; %set the data pointer to the begining of the read data
% read in each successive scanline */
for scanline=1:num_scanlines
% if mod(scanline,fix(num_scanlines/100))==0
% fprintf('scanline = %d\n',scanline);
% end
%
if (data(dp) ~= 2) || (data(dp+1) ~= 2)% || (bitget(data(dp+2),8)~=1)
error('this file is not run length encoded');
end
if (bitshift(data(dp+2),8)+data(dp+3))~=scanline_width % -128
error('wrong scanline width');
end
dp = dp+4;
% read each of the four channels read the scanline into the buffer
for i=1:4
ptr = 1;
while(ptr <= scanline_width)
if (data(dp) > 128) % a run of the same value
count = data(dp)-128;
if ((count == 0) || (count-1 > scanline_width - ptr))
warning('bad scanline data');
end
scanline_buffer(ptr:ptr+count-1,i) = data(dp+1);
dp = dp+2;
ptr = ptr+count;
else % a non-run
count = data(dp);
dp = dp+1;
if ((count == 0) || (count-1 > scanline_width - ptr))
warning('bad scanline data');
end
scanline_buffer(ptr:ptr+count-1,i) = data(dp:dp+count-1);
ptr = ptr+count;
dp = dp+count;
end
end
end
% now convert data from buffer into floats
img(scanline,:,:) = rgbe2float(scanline_buffer);
end
% standard conversion from float pixels to rgbe pixels
% the last dimension is assumed to be color
function [rgbe] = float2rgbe(rgb) %#ok<DEFNU>
s = size(rgb);
rgb = reshape(rgb,prod(s)/3,3);
rgbe = reshape(repmat(uint8(0),[s(1:end-1),4]),prod(s)/3,4);
v = max(rgb,[],2); %find max rgb
l = find(v>1e-32); %find non zero pixel list
rgbe(l,4) = uint8(round(128.5+log(v)/log(2))); %find E
rgbe(l,1:3) = uint8(rgb(l,1:3)./repmat(2.^(double(rgbe(l,4))-128-8),1,3)); %find rgb multiplier
reshape(rgbe,[s(1:end-1),4]); %reshape back to original dimensions
% standard conversion from rgbe to float pixels */
% note: Ward uses ldexp(col+0.5,exp-(128+8)). However we wanted pixels */
% in the range [0,1] to map back into the range [0,1]. */
function [rgb] = rgbe2float(rgbe)
s = size(rgbe);
rgbe = reshape(rgbe,prod(s)/4,4);
rgb = zeros(prod(s)/4,3);
l = find(rgbe(:,4)>0); %nonzero pixel list
rgb(l,:) = double(rgbe(l,1:3)).*repmat(2.^(double(rgbe(l,4))-128-8),1,3);
rgb = reshape(rgb,[s(1:end-1),3]);
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