...but on the other hand, with a high enough quality photograph, and a low enough resolution original image... it sure seems possible.
The first pass might be off - I can imagine adjusting the grid size to skip the scan lines for more accuracy. But the final result will be very close with 5% of the work involved. The guy has spent a day and a half for a task that should take less than an hour at most.
Even non-fisheye lenses have some distortion, but look at how wacky the grid can appear here:
https://docs.nvidia.com/vpi/image-003.jpg
And it gets worse if you only see the grid, and don't know how it was cropped out of the photo it was taken from (if it was off-center).
But yeah, I think we're all on the same page that some entrepreneurial image processing expert could make fairly quick work of the problem.
Even if they were distorted by a fisheye lens, it should be easy to use something like Photoshop's "pinch" filter to create an undistorted image to work from.
https://live.staticflickr.com/65535/50926604693_1e6b65f13b_b...
1. Color correct for the CMYK printing process
2. Load image as a pixel matrix
3. Unwrap pixel matrix into a pixel vector
4. Convert the pixel vector to HSV representation
5. Group each pixel into a palette slot by plugging the H/S dimensions into K-means with 32 as the target (ignoring L for clustering to account for scanlines/flicker)
6. For each palette slot, calculate the "true" HSV value by taking the group's median H/S values and the mean V value
7. Convert HSV representation to 12-bit RGB colorspace