Chromatic aberrations fix example ?

[pypoulp]

Hello,

Those python bindings to lensfun look pretty cool!

What is the workflow for fixing chromatic aberration / vignetting? (I need to fix chromatic aberrations, but not large distortion). It's not really clear in the API docs.

Thanks.

Paul.

[letmaik]

Vignetting and chromatic aberration are different things. Vignetting corrections (via lensfun's lfModifier::ApplyColorModification(..)) are not exposed through lensfunpy yet, feel free to open a separate issue if you need this functionality.

For correcting chromatic aberrations you would have to use undist_coords = mod.apply_subpixel_distortion() which gives you the undistortion coordinates per image channel. I'm not sure if you can use cv2.remap directly here or whether you have to apply it separately per-channel, probably the latter. If you figure it out, please post it here and I'll include it in the samples.

[pypoulp]

Thanks for reply,
For some reason, the undist_coords = mod.apply_subpixel_distortion() method gives me a numpy array full of 0. tried multiple lens / cameras.
code used :

mod = lensfunpy.Modifier(lens, 1.0, width, height)
mod.initialize(focal_length, aperture, distance,  flags=lensfunpy.ModifyFlags.ALL)
undist_coords = mod.apply_subpixel_distortion()
print(np.max(undist_coords))  # => 0.
print(np.min(undist_coords))  # => 0.

[letmaik]

Can you check at http://lensfun.sourceforge.net/lenslist/ whether your lens has a "yes" at the TCA column? If not, then that's the reason, and I guess this could be surfaced better with a useful error message. If yes, then it's a bug I think.

[pypoulp]

You're right, TCA wasn't available for this lens. undist_coords seems correct with a valid TCA calibrated lens.

It's kind of wierd, but with subpixel coords, cv2.remap (per channel) is going pretty crazy, rotating the green channel 90°. need a bit more investigation to get it working.

# OpenCV is BGR order

r = im[..., 2]
g = im[..., 1]
b = im[..., 0]

r_undistorted = cv2.remap(r, undist_coords[..., 0], None, cv2.INTER_LANCZOS4)
g_undistorted = cv2.remap(g, undist_coords[..., 1], None, cv2.INTER_LANCZOS4)
b_undistorted = cv2.remap(b, undist_coords[..., 2], None, cv2.INTER_LANCZOS4)

im[..., 2] = r_undistorted
im[..., 1] = g_undistorted
im[..., 0] = b_undistorted


cv2.imwrite(undistorted_image_path, im)

[CapPow]

@paulparneix, I may have a (late) solution for you. It seems swapping the axes on the green channel solves the issue, although I don't know why.

r = im[..., 2]
g = im[..., 1].swapaxes(0,1)
b = im[..., 0]

[letmaik]

Fixed in #44 and will be part of the next release. With that fix, it would be (note undist_coords slicing):

# OpenCV is BGR order

r = im[..., 2]
g = im[..., 1]
b = im[..., 0]

r_undistorted = cv2.remap(r, undist_coords[..., 0, :], None, cv2.INTER_LANCZOS4)
g_undistorted = cv2.remap(g, undist_coords[..., 1, :], None, cv2.INTER_LANCZOS4)
b_undistorted = cv2.remap(b, undist_coords[..., 2, :], None, cv2.INTER_LANCZOS4)

im[..., 2] = r_undistorted
im[..., 1] = g_undistorted
im[..., 0] = b_undistorted

cv2.imwrite(undistorted_image_path, im)