How can I read lossy jpeg compressed sequence (seq) files?

EDIT: I solved it, please see file exchange link below

I have have a very big amount of compressed SEQ data (lossy jpg, ~60 TB) that I have to export to AVI with StreamPix (NorPix) prior to analysis in Matlab. I could save a lot of HDD space if I could read the compressed images in the SEQ file directly.

I was able to read a test sequence (see attachment) header using the code from

http://www.norpix.com/support/faq.php#matlab

Output:

              Version: 5
           HeaderSize: 8192
          Description: 'StreamPix 7.4.0.0 (x64)'
           ImageWidth: 640
          ImageHeight: 480
        ImageBitDepth: 8
    ImageBitDepthReal: 8
       ImageSizeBytes: 307200
          ImageFormat: 'Monochrome'
      AllocatedFrames: 153
               Origin: 0
        TrueImageSize: 921608
            FrameRate: 20.1316
          Compression: 1

but I am not able to recreate an image apart from random pixels.

I have in mind that image size is variable in compressed SEQ. Can someone give me a hint of what could help? Does one generally have to uncompress the image in order to read it (eg. Decoding, Dequatization, Inverse DCT, Upsampling, Color Transform)?

Thanks and regards, Paul

Code:

fid = fopen(fileName,'r','b');
% Use the Little Endian machine format ordering for reading bytes
endianType = 'ieee-le';

% Read header

OFB = {28,1,'long'};
fseek(fid,OFB{1}, 'bof');
headerInfo.Version = fread(fid, OFB{2}, OFB{3}, endianType);
% headerInfo.Version

%
OFB = {32,4/4,'long'};
fseek(fid,OFB{1}, 'bof');
headerInfo.HeaderSize = fread(fid,OFB{2},OFB{3}, endianType);
if  headerInfo.Version >=5
    display('Version 5+ detected, overriding reported header size')
    headerInfo.HeaderSize = 8192
end
% headerInfo.HeaderSize

%
OFB = {592,1,'long'};
fseek(fid,OFB{1}, 'bof');
DescriptionFormat = fread(fid,OFB{2},OFB{3}, endianType)';
OFB = {36,512,'ushort'};
fseek(fid,OFB{1}, 'bof');
headerInfo.Description = fread(fid,OFB{2},OFB{3}, endianType)';
if DescriptionFormat == 0 %#ok Unicode
    headerInfo.Description = native2unicode(headerInfo.Description);
elseif DescriptionFormat == 1 %#ok ASCII
    headerInfo.Description = char(headerInfo.Description);
end
% headerInfo.Description

%
OFB = {548,24,'uint32'};
fseek(fid,OFB{1}, 'bof');
tmp = fread(fid,OFB{2},OFB{3}, 0, endianType);
headerInfo.ImageWidth = tmp(1);
headerInfo.ImageHeight = tmp(2);
headerInfo.ImageBitDepth = tmp(3);
headerInfo.ImageBitDepthReal = tmp(4);
headerInfo.ImageSizeBytes = tmp(5);
vals = [0,100,101,200:100:600,610,620,700,800,900];
fmts = {'Unknown','Monochrome','Raw Bayer','BGR','Planar','RGB',...
    'BGRx', 'YUV422', 'YUV422_20', 'YUV422_PPACKED', 'UVY422', 'UVY411', 'UVY444'};
headerInfo.ImageFormat = fmts{vals == tmp(6)};
%
OFB = {572,1,'ushort'};
fseek(fid,OFB{1}, 'bof');
headerInfo.AllocatedFrames = fread(fid,OFB{2},OFB{3}, endianType);
% headerInfo.AllocatedFrames

%
OFB = {576,1,'ushort'};
fseek(fid,OFB{1}, 'bof');
headerInfo.Origin = fread(fid,OFB{2},OFB{3}, endianType);
% headerInfo.Origin

%
OFB = {580,1,'ulong'};
fseek(fid,OFB{1}, 'bof');
headerInfo.TrueImageSize = fread(fid,OFB{2},OFB{3}, endianType);
% headerInfo.TrueImageSize

%
OFB = {584,1,'double'};
fseek(fid,OFB{1}, 'bof');
headerInfo.FrameRate = fread(fid,OFB{2},OFB{3}, endianType);
% headerInfo.FrameRate

%
OFB = {620,1,'uint8'};
fseek(fid,OFB{1}, 'bof');
headerInfo.Compression = fread(fid,OFB{2},OFB{3}, endianType);
% headerInfo.Compression 

imageOffset = 8192;
imgOut = uint8(zeros(headerInfo.ImageWidth,headerInfo.ImageHeight));
    switch headerInfo.ImageBitDepthReal
        case 8
            bitstr = 'uint8';
        case {10,12,14,16}
            bitstr = 'uint16';
    end
nread = 0;
fseek(fid, imageOffset + nread * headerInfo.TrueImageSize, 'bof');
numPixels = headerInfo.ImageWidth * headerInfo.ImageHeight;
Vec = fread(fid, numPixels, bitstr, endianType);
img= reshape(Vec,headerInfo.ImageWidth,headerInfo.ImageHeight)';
I = uint8(img);
imshow(I);

Answer 1

[Paul Siefert]

Find my solution here:

http://de.mathworks.com/matlabcentral/fileexchange/68341-readcompressedjpegseq

[Walter Roberson]

Thanks, Paul.