pythonimage-processingmatplotlibdng

DNG raw pictures imported as 16 bit deep but unexpected plt.show() result

Trying to process raw DNG pictures in Python with rawpy ends with strange results.

import rawpy
import imageio
from matplotlib import pyplot as plt

path = '/home/stefan/AIJ/RAW.DNG'
with rawpy.imread(path) as raw:
    rgb = raw.postprocess()
plt.imshow(rgb)
plt.show()

The result is an rgb picture array with 8-bit values while my camera generates 14 bit raw pictures.

Visualizing the rgb array gives an expected result:

enter image description here

From some googleing I understood that it is possible to import the same file but with an output in 16-bit.

I used the following parameters in the postprocess function:

rgb = raw.postprocess(output_bps=16,demosaic_algorithm=None,output_color = rawpy.ColorSpace.Adobe)

Now the rgb array contains 16 bit values but visualizing results in the following:

enter image description here

Could someone tell me how I could obtain a visualization similar to the first result but handling 16-bit values?

Initially I thought it was related to the fact that my camera is producing 14 bit images rather than 16 bit, but changing the parameter output_bps into 14 gives even worse visualization results.

Thanks in advance!

On request, I would add here the raw picture from a PENTAX K-5 but it is 18MB big and the forum has a limit of 2MB (may be another way to pass you the file?).

Solution

  • I don't think the issue has to do with how you are reading the image, as imshow does not display 16-bit RGB images. So, if you are interested in visually checking the results of reading in the 16-bit image, I would suggest either inspecting bands individually, with

    plt.imshow(rgb[:, :, 0])

    and so on for each band; or converting the rgb to 8-bit and displaying that, with

    rgb8 = (rgb / 256).astype('uint8')
plt.imshow(rgb8)