Matlab DNG image processing: CFA extraction results in black image

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 = getImageInfo('camera_raw.dng');
tiffObj = openTiffFile('camera_raw.dng', 'read');
subDirectories = tiffObj.getSubDirectories();
tiffObj.setActiveSubDirectory(subDirectories(1));
colorFilterArray = double(tiffObj.readCurrentImage());

When I run this, colorFilterArray is a matrix of zeros. If I plot it, I just get a black image. What am I doing wrong? How can I correctly extract the Bayer array from my DNG file?

I thought this approach would work based on some examples I’ve seen, but clearly I’m missing something. Any help would be greatly appreciated!

2

Hey there! I’ve been tinkering with DNG files in Matlab too, and I totally get your frustration. :sweat_smile:

Have you considered that the raw data might be hiding in a different subdirectory? DNG files can be tricky like that! Maybe try looping through all the subdirectories to find where the juicy bits are:

for i = 1:length(subDirectories)
    tiffObj.setActiveSubDirectory(subDirectories(i));
    if tiffObj.getTag('ImageLength') ~= 0
        colorFilterArray = double(tiffObj.readCurrentImage());
        break;
    end
end

Also, raw data is usually 16-bit, so you might need to scale it properly. Something like this could work:

colorFilterArray = colorFilterArray / 65535;

Have you tried playing around with the dcraw library? I’ve heard it’s pretty nifty for handling raw files. Might be worth a shot if you’re still stuck!

What camera are you using, by the way? Some brands can be extra quirky with their DNG formats. Let me know if you make any progress – I’m super curious to see how this turns out!

3

I’ve encountered similar issues when working with DNG files in MATLAB. One thing to check is whether you’re accessing the correct subdirectory. DNG files often have multiple subdirectories, and the raw data might not be in the first one.

Try iterating through all subdirectories and checking their contents:

for i = 1:length(subDirectories)
    tiffObj.setActiveSubDirectory(subDirectories(i));
    info = tiffObj.getTag('ImageLength');
    if info ~= 0
        colorFilterArray = double(tiffObj.readCurrentImage());
        break;
    end
end

Also, ensure you’re handling the data type correctly. Raw images are usually 16-bit, so you might need to scale the data:

colorFilterArray = double(tiffObj.readCurrentImage()) / 65535;

If you’re still having trouble, consider using a specialized library like dcraw for more robust raw image processing.

4

hey mate, have u tried checking different subdirectories? sometimes the raw data isnt in the first one. also, make sure ur scaling the data right - raw images are usually 16-bit. try something like:

colorFilterArray = double(tiffObj.readCurrentImage()) ./ 65535;

that might help get rid of the black image problem. good luck!