Converting CFA sensor data to a raw image file

CFA
1

Hey everyone, I’m stuck on a problem with saving CFA sensor data as a raw image file. I want to use PIL to save the 8-bit per pixel CFA buffer as a raw file that I can later process with LibRaw or dcraw.

I’ve tried saving it as a .raw or .tiff file using PIL, but I can’t load it afterward. When I use numpy’s imread, it looks like each pixel has the same value for r, g, and b.

Here’s what I’ve tried so far:

 def save_cfa_data(input_data):
     with open(input_data, 'rb') as f:
         data = f.read()
      
     processed_data = bytearray(data)
      
     with open('output.raw', 'wb') as f:
         f.write(processed_data)
      
     img = Image.frombuffer('P', (4096, 3072), processed_data, 'raw', 'P', 0, 1)
     img.convert('L').save('grayscale_output.tiff')

Any ideas on how to correctly save this CFA data as a raw image file? Thanks in advance for your help!

2

I’ve encountered a similar situation with CFA sensor data, and the trick is often in how the raw bytes are reshaped and processed. Since each pixel in CFA data only records one color, you need to create a 2D array that matches your sensor’s dimensions.

One effective approach is to use numpy to read and reshape the data, then save it as a 16-bit TIFF file. This format can retain the full data for processing tools like LibRaw or dcraw.

import numpy as np
from PIL import Image

def save_cfa_data(input_data, width, height):
    with open(input_data, 'rb') as f:
        data = np.fromfile(f, dtype=np.uint8)
    reshaped_data = data.reshape((height, width))
    img = Image.fromarray(reshaped_data, mode='I;16')
    img.save('output.tiff', format='TIFF')

This method should help resolve the issue.

3

Hey there DancingButterfly! :wave:

I totally get your frustration with CFA data. It can be a real head-scratcher sometimes!

Have you considered using the rawpy library? It’s pretty nifty for handling raw image data. Here’s a little snippet that might help:

import rawpy
import numpy as np

def save_cfa_data(input_data, output_file):
    raw_data = np.fromfile(input_data, dtype=np.uint8)
    raw_data = raw_data.reshape((3072, 4096))
    
    with rawpy.imread(input_data) as raw:
        raw.raw_image[:] = raw_data
        raw.save(output_file)

This should preserve the CFA pattern and give you a file that plays nice with LibRaw and dcraw.

What kind of camera are you working with, by the way? Different sensors can have quirks that might affect how you handle the data.

Let me know if this helps or if you need any more info! Always happy to brainstorm on tricky image processing stuff. :blush:

4

hey dancingbutterfly, i had similar trouble. try using numpy to handle the data. something like:

import numpy as np
raw_data = np.fromfile('input.raw', dtype=np.uint8)
raw_data = raw_data.reshape((3072, 4096))
np.save('output.npy', raw_data)

this should keep the original cfa pattern intact. good luck!