4 ms·

The blurring and then sharpening in spatial domain is equivalent to applying a band-pass filter, or rather a band-stop in the article's case, in the frequency d

by a_c 5y ago

The blurring and then sharpening in spatial domain is equivalent to applying a band-pass filter, or rather a band-stop in the article's case, in the frequency domain. Blurring requires a lot of parameter tuning, in particular the size of the mask and the weight of each the mask element. The choice of parameter can be mapped to particular filter in the frequency domain, e.g. a gaussian filter or an ideal filter. Same for sharpening. Operating in the frequency domain allows you to skip all the trial and error of parameters, by eye-balling the frequency of interest, and suppress its presence. > what you did is still the best out there It still is. I worked with a printing company before. The company impart anti-forgery pattern to packaging material by tuning the half tone-ing angle of the printer. The printing company then offer a seemingly transparent film, with special pattern printed on it, to company requiring brand protection. By overlaying the film on top of packaging material, a specifically designed moire pattern would occur. If you squint your mind enough, it is like public-private key encryption in the physical world. Whenever the brand receive dispute over authenticity of purchased items, a special team, a team having that transparent film, will be summoned to verify the authenticity of item in question. It is one of the many ways the brand in question protect their goods. The printing company was looking for a mobile solution instead of delivery the transparent film, that's where I get to learn more about the printing industry.

lbotos 5y ago
are you at liberty to share the printing company here? I'm looking for something like this. If not, my email is in my profile and would appreciate info so I can reach out and maybe give them business!
- a_c 5y ago
  Thing is a bit complicated. I actually worked with a middleman, this middleman act as the "certificate authority" - signing up brands and dispatching orders to printing company(ies). So the printing companies don't know what the matching pattern is. It was five years ago and I have since moved on.
- mceachen 5y ago
  20 years ago you could just type in the rotation angle you wanted for each color separation into your film plotter. If you ask your printer, they should be able tell you what lpi/dpi they can resolve on the media you're printing onto (you may be limited due to dot gain on uncoated stock).
a_c 5y ago
> It still is. It is a relatively well defined problem - removing periodic pattern due to physical arrangement of printing device. This is where algorithmic approach shines over ML approach. I think nowadays a lot of ML is an attempt to outsource the problem understanding part. These are hot dogs, these are not hot dogs. I don't know what defines a hot dog, but is this picture a hot dog? Hyperbole, of course. On second thought, I think the author shouldn't remove the periodic noise at all. He was preserving "a copy of history", not the first occurrence of history. It is a property worth preserving. It is a beauty of itself imo.
- II2II 5y ago
  The moire is an artifact of the scanning or scaling process, and is by no means historic. Removing it is certainly legitimate. That is particularly true since scaling the image can make it worse. If you are talking about preserving the halftone in an original scan, then yes I agree that it should be preserved. Yet you must also accept that the periodic pattern will have to be removed prior to publishing the image since it will be scaled at some point.
  - imoverclocked 5y ago
    It would be cool if the photo could be printed in a similar way to re-create the effect from the recovered image.
- derefr 5y ago
  The halftone pattern itself might look lovely and “historical” on you screen, but the book would not present the image “as-is” (i.e. with all halftone detail from the original photo losslessly captured on the page), but rather through the lens of another halftone printing process, one whose DPI is low-enough that it would arbitrarily interfere with the original photo’s to create a garbled mess. The final product wouldn’t be halftone dots encoding a picture, but rather halftone dots encoding moire stripes from an attempt to replicate other halftone dots from a “sample grid” that doesn’t line up with them. It’d be a bit like taking one of those game emulators that displays the game with a “scanline”-effect filter… and then hooking the computer running the emulator up to an old TV that has a natural built-in scanline effect. You won’t get the pretty scanlines from the emulator, nor will you get the pretty scanlines from the TV; you’ll just get a mess. (To put it in technical terms: to accurately show the halftone “information” from the original photo in the book, the print resolution of the book would need to be double the Nyquist frequency of said halftone information. But it very likely won’t be.)
MihaiSandor 5y ago
“I have had my results for a long time: but I do not yet know how I am to arrive at them” - C.F Gauss. Nice job a_c

by a_c 5y ago

lbotos 5y ago

are you at liberty to share the printing company here? I'm looking for something like this. If not, my email is in my profile and would appreciate info so I can reach out and maybe give them business!

a_c 5y ago
Thing is a bit complicated. I actually worked with a middleman, this middleman act as the "certificate authority" - signing up brands and dispatching orders to printing company(ies). So the printing companies don't know what the matching pattern is. It was five years ago and I have since moved on.
mceachen 5y ago
20 years ago you could just type in the rotation angle you wanted for each color separation into your film plotter. If you ask your printer, they should be able tell you what lpi/dpi they can resolve on the media you're printing onto (you may be limited due to dot gain on uncoated stock).

a_c 5y ago

> It still is. It is a relatively well defined problem - removing periodic pattern due to physical arrangement of printing device. This is where algorithmic approach shines over ML approach. I think nowadays a lot of ML is an attempt to outsource the problem understanding part. These are hot dogs, these are not hot dogs. I don't know what defines a hot dog, but is this picture a hot dog? Hyperbole, of course. On second thought, I think the author shouldn't remove the periodic noise at all. He was preserving "a copy of history", not the first occurrence of history. It is a property worth preserving. It is a beauty of itself imo.

II2II 5y ago
The moire is an artifact of the scanning or scaling process, and is by no means historic. Removing it is certainly legitimate. That is particularly true since scaling the image can make it worse. If you are talking about preserving the halftone in an original scan, then yes I agree that it should be preserved. Yet you must also accept that the periodic pattern will have to be removed prior to publishing the image since it will be scaled at some point.
- imoverclocked 5y ago
  It would be cool if the photo could be printed in a similar way to re-create the effect from the recovered image.
derefr 5y ago
The halftone pattern itself might look lovely and “historical” on you screen, but the book would not present the image “as-is” (i.e. with all halftone detail from the original photo losslessly captured on the page), but rather through the lens of another halftone printing process, one whose DPI is low-enough that it would arbitrarily interfere with the original photo’s to create a garbled mess. The final product wouldn’t be halftone dots encoding a picture, but rather halftone dots encoding moire stripes from an attempt to replicate other halftone dots from a “sample grid” that doesn’t line up with them. It’d be a bit like taking one of those game emulators that displays the game with a “scanline”-effect filter… and then hooking the computer running the emulator up to an old TV that has a natural built-in scanline effect. You won’t get the pretty scanlines from the emulator, nor will you get the pretty scanlines from the TV; you’ll just get a mess. (To put it in technical terms: to accurately show the halftone “information” from the original photo in the book, the print resolution of the book would need to be double the Nyquist frequency of said halftone information. But it very likely won’t be.)

MihaiSandor 5y ago

“I have had my results for a long time: but I do not yet know how I am to arrive at them” - C.F Gauss. Nice job a_c