Vignette correction #4419
Replies: 3 comments 1 reply
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OK, I'm back on track and leaving this here for posterity. The above has two primary issues:
The following appears to be correct (subject to more testing) width = Image.width(image)
height = Image.height(image)
centre_x = (width - 1) / 2
centre_y = (height - 1) / 2
# Cartesian coordinates of the destination point
# relative to the centre of the image.
index = Vips.xyz!(width, height)
index = (index - [centre_x, centre_y])
r = pow!(index[0]**2 + index[1]**2, 0.5)
# Normalise the radius
{max, _} = Vips.max!(r)
r = r / max
# Correction function from https://lensfun.github.io/calibration-tutorial/lens-vignetting.html
# Also http://download.macromedia.com/pub/labs/lensprofile_creator/lensprofile_creator_cameramodel.pdf
# Cd = Cs * (1 + k1 * R^2 + k2 * R^4 + k3 * R^6)
# Inverting the formula to un-vignette (rather than calibrate the vignette)
d_dest = 1.0 - (k1 * r**2) + (k2 * r**4) + (k3 * r**6)
Image.cast!(image / d_dest, :u8)
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Hi @kipcole9, I've always used a cosine for this, but I guess a parabola works as well. It probably doesn't matter much. In ruby you could write: #!/usr/bin/ruby
require 'vips'
image = Vips::Image.new_from_file ARGV[0], access: :sequential
vignette = Vips::Image.xyz image.width, image.height
# move origin to centre
vignette = vignette - [image.width / 2, image.height / 2]
# to polar, then take just distance
vignette = vignette.polar[0]
# raised cosine
vignette = (vignette * (ARGV[2].to_f / image.width)).cos
# apply to image
image = image * vignette
image.write_to_file ARGV[1]ie. use Your parabola function is probably quicker and just as good. |
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I think you could improve: You don't need to search the radius image, you can just calculate this value from the image width and height. |
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Thanks as always John. The parabola comes from matching to the parameters from |
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I'm working to add vignette correction to image using the correction data from lensfun.
I've implemented what I think is the right algorithm, but clearly I've messed up somewhere. Hoping someone with more knowledge than me (pretty much everyone) can give me some guidance.
Here's an example. It's in Elixir but I think its readable to anyone who has worked with Ruby or Python.
This results in the following image. The image darkens (rather than lightens) towards the edges. And the corners aren't correct either (I think).
Any and all guidance warmly appreciated.
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