I couldn't let another FFT thread pass by without sticking my nose in....
To our eyes the "golf balls" seem to be exactly repetitive and using FFT you will be able to remove all the repeating frequencies. What you have got left after that is noise that was superimposed on those frequencies.
Although we can see some sort of pattern in this noise, it doesn't repeat any more - there are some white dots, then a few black ones......
Why is this one different? Because other paper textures are usually less embossed than this one and don't pick up so much dirt (=noise).
For those (few, OK) mathematically inclined.. there is actually a way to calculate where the stars will be in the FFT. Something like.. measure the pixel distance between the texture ridges, divide the total image dimension by this number, then count out from the centre. I did have it figured out once and it did work.
(Yeah, I know - 1.496Km to go)
Repeat: Fovea wasn't intended for you guys
I never intended for this to be an ad for Fovea -- it is a general purpose image analysis system for scientific imaging.
Now, some of the things in there (like the Fourier suite) *might* make an interesting product at a more acceptable price, but I need to see what you guys want/need/are willing to learn.
My basic inclination is to completely hide the FFT under-the-hood, whether for deconvolution (Optipix->Refocus), using an ideal inverse (a very neat tool for image enhancement), halftone removal, etc.
The learning curve, for one, is huge. Two, the Fourier suite works in b&w. Three, there are 177 plugins in Fovea. Four, the "tutorial" is 500 pages.
Then, again, it might be interesting to see how he feels after going through it. <evil laughter>
That's how Chris and I first connected. A couple of years ago I was looking for focus and pattern solutions and came across Fovea Pro. We exchanged some emails and I even printed out the manual and made an attempt at figuring it out. But it was written from the perspective of a place I've never been (technical image analysis), and I was quickly in way over my head.
But I do feel there is a valuable restoration tool waiting to be designed, here. Something without painted stars, with sliders (and a realtime preview). Perhaps something that would internally rank the patterns and let you page through them ("no, don't remove that one, yes, remove that one and that one, but leave that one").
The Cheryl Tiegs assignment was inspired
(I had already read through most of your site, and numbers and formulas don't scare me - I almost majored in maths)
Median filter to remove stuff
Phil showed an example of using a radius=3 median filter to remove stuff. If you think about a median filter, let's start with the simplest radius=1 (3x3 neighborhood), it will remove lines that are 1 pixel wide or clusters that are less than 9/2 =4.5 pixels. So a block that is 2x2 will be completely removed as will the thinnest of lines.
As this neighborhood radius gets larger (he used an example of radius=3 - 7x7 neighborhood, lines that are 3 pixels wide or narrower will get removed, blocks that are less than 49/2 or 24.5 pixels will be removed, and corners on objects will be rounded off. This is why you were able to remove the pattern with a median filter. It is a really harsh filter, though, in that it removes all kinds of useful stuff.
There is a variation on the median called a "Hybrid Median" that is nowhere near as harsh. We've implemented it in FoveaPro, but also in Optipix as "Safe Median." Basically it is much more computationally intensive, but can preserve lines and corners. It still does a good job at removing noise (and, regretfully, fine detail).
We probably should have a discussion about noise removal and what is noise and what isn't. It might be fun to write a couple of plugins for you guys to play with to see what we can learn. (I like having guinea pigs!)
Thanks for the suggestion of median filter. This is quick and easy and has removed all the texture but has sacrificed detail (look at the eyes)
You have retained all the detail but have left a little texture (or is this noise byRo)
If FFT had worked perfectly your first step would not be necessary
Your image has more contrast than Jcr6
Your picture still looks good. You have removed all the texture
Thanks very much for your excellent contribution.
Your picture is great. Although there is still a little texture/noise you have retained all the detail (not that there is much in this image)
Duv has got a similar result but with a little more contrast
I’ve downloaded FoveaPro trial and will read Tutorial5.pdf
What you have written here has already taught me a lot
OK here are my new steps
1) Set background colour to grey 127,127,127 (for Padding)
2) Image > Canvas Size > 512,512 in Pixels (In this case - square with dimension equal to an exact power of two)
3) Image > Adjust > Desaturate
4) Filter > FFT RGB
5) On the Red Channel > clone (using Darken) out the Stars except middle one
6) Blur step here? (Butterworth?)
7) Filter > IFFT RGB
Is this OK? My results Have improved
I have a few Questions
I am (now) Using FFT_RGB_PlugIns_13April_2005. Is this the version everyone else is using? And is this the correct version?
The corners are missing. Is this significant?
Step 6) Any suggestions?
You suggest starting with a B&W image. Do you mean Greyscale or RGB>Desaturated. My Fourier Transform Folder is unavailable with a Greyscale Image
In the UK Ilford used to make a paper called Velvet Stipple. This was one of the most textured papers available. Does anyone have a sample for Jcr6 to deconstruct.
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