Matlab DNG image processing: CFA extraction yields black output

CFA
1

I’m trying to extract the Color Filter Array from a DNG file using Matlab. Here’s the code I’m using:

imageInfo = getImageDetails('camera_shot.dng');
tiff = openTiffFile('camera_shot.dng', 'read');
subDirOffsets = tiff.fetchTag('SubDirectory');
tiff.moveToSubDir(subDirOffsets(1));
colorFilterArray = convertToDouble(tiff.readImage());

When I run this, colorFilterArray is just zeros, showing up as a black image when plotted. I’m confused about why this is happening. Does anyone know how to properly extract the Bayer array from a DNG file in Matlab? I’d really appreciate any help or suggestions!

2

hey owen, ive run into this before. make sure ur dng file isnt compressed. also, try checkin different subIFDs - the CFA might be hidin somewhere else. u could use a loop to go thru all subIFDs til u find non-empty data. if that dont work, maybe look into usin a specific DNG library for matlab. good luck!

3

I’ve dealt with similar issues when working with DNG files in MATLAB. One thing to consider is that the CFA data might be stored in a different subIFD than you’re currently accessing. Try iterating through all the subIFDs to locate the raw image data.

Additionally, check if your DNG file has been compressed. Some cameras apply lossless compression to the raw data, which needs to be decompressed before you can access the CFA.

Here’s a snippet that might help:

for i = 1:length(subDirOffsets)
    tiff.moveToSubDir(subDirOffsets(i));
    try
        colorFilterArray = tiff.readImage();
        if ~isempty(colorFilterArray)
            break;
        end
    catch
        % Skip if error occurs
    end
end

If this doesn’t work, you might need to look into using a specialized DNG library or tool that can handle various DNG formats and compression methods. Let us know if you make any progress!

4

Hey there, Owen_Galaxy! That’s an interesting problem you’ve got there with DNG file processing. I’m curious, have you tried checking the metadata of your DNG file? Sometimes the CFA information might be stored differently depending on the camera model or DNG version.

Maybe we could troubleshoot this together? What camera are you using to capture these DNG files? And have you confirmed that the DNG file actually contains raw sensor data and not a processed image?

One thing you might want to try is using the ‘imfinfo’ function in MATLAB to get more details about your DNG file. It might give you some clues about where the CFA data is stored.

Also, just throwing this out there - have you considered using any existing DNG processing libraries for MATLAB? There might be some ready-made solutions that could save you some headaches.

Let me know what you find out! I’m really curious to see how you solve this.