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There are many approximations for the Laplacian Filter (See The Hypermedia Image Processing Reference - Laplacian/Laplacian of Gaussian):
Indeed this is an High Pass Filter. Namely it will remove low frequencies (Specifically it will remove the DC Value, namely the output image will have mean value of 0).
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The amplitude of an image represents the intensity of the different frequencies in the image. Therefore, it holds the geometrical structure of features in the image (i.e. changes in the spatial domain).
The phase on the other hand, represents the locations of these features (which helps our human eye to better comprehend the image).
Here's a visualization I ...
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Pay attention that convolution mean flipping the kernel both on the x and y axis.
Hence the first element is a multiplication of $ -1 \cdot -1 $ which yields $ 1 $ as in the answer in the original post.
Pay attention that this is a discrete approximation of the gradient based on Finite Differences. This specific one is based on the Sobel 1st derivative ...
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http://r0k.us/graphics/kodak/ does link to Kodak PhotoCD contents with 2048x3072 images.
It is not what is called "raw" as those are using 4:2:0 subsampling (so not lossless at all) and xvYCC transfer function (almost like BT.709 gamma). Those were indeed produced by scanning KODACOLOR Gold 100 (35 mm) film and some other types of 35 mm, all types ...
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"Target" is a military term; historically, that's why it's the word used for "identifiable thing from a radar system".
So, I wouldn't use "target detection" outside of radar systems, whereas the word "object detection" is generally used in image processing (for anything that isn't a person). I might be a bit alone with ...
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For part 3, there is an old trick dating from the time where computing was expensive. If you have a smoothed version $I_\sigma$ of a picture $I$, you can get a crude yet simple approximation of a Laplacian from $I -I_\sigma$, illustrated here with the Gaussian:
It is indeed generalized in many unsharp filters, with other weights, or in multirate/multiscale ...
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One possible answer to my own question is provided by the photographic scale reference detailed on this website.
https://smallpond.ca/jim/scale/
It doesn't quite provide the solution I was looking for, buy may help spur ideas. I really need something that can accommodate a good scale estimate even if the reference is rotated in space (about any of the three ...
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