Nice work, Ken.
Like I say (or maybe it was Doug) - the best way to learn something is to write a tutorial about it.
Mmmm. I'm finding with the original posted image that I'm getting texture showing thru from the base layer. Luminosity looked pretty clean. Is the texture too strong or something else I can do?
Hi Ken, still having problems getting Winrar to download. Can get the home page OK, download page OK, but can't get the Winrar file to download. Browser just times out. Have tried using both Firefox and IE.
Though the technicalities of FFT is beyond my comprehension, I would like to mention two softwares which I found useful for editing out the unwanted patterns/textures; Astra Image and ImageJ. FFT editing can done only in grayscale mode. The interface is similar to what Cameraken has attached above.
Two samples of fft edited picture is also being attached. The first one has been done in AstraImage with plain FFT editing. The second, done in ImageJ has gone through adjusting of Brightness/Contrast and applying of Median filter at a setting of 2.
I agree with you I can’t quite get results as good as jcr6. Perhaps this is the difference between 0$ and 799$
As I said right at the start I thought jcr6 provided the best results
Floras has obviously been manipulated so its hard to compare.
Perhaps someone will have the time to compare FFT RGB with FoveaPro FFT
We may have to rely on byRo and jcr6 for the answers.
As I pointed out this picture is a tiny portion of a much larger image and it was given to me rolled up. I suppose that an invisible crease or stretch in the paper could very easily spoil the mathematics of removing a fixed pattern.
We used to mount a lot of our studio photographs using Ademco dry mounting tissue and an Ademco press. We used to use a tacking iron to tack the photo into place before placing it in the press. I am sure that this process would now cause a problem for FFT. As there will be parts of the print with a slightly different texture
Note to Rô and a way to do low & high pass filters
1023 (presumably the horizontal direction) is 3 x 11 x 31, but that would run at nearly full speed since a whole line should fit in the L1 cache on your computer. 2047 is 23 x 89, but there is already a large delay in vertical accesses through the image, so you might not see a delay that is significantly worse than memory accesses already are. (Isn't caching fun!) Perhaps we should do benchmarks and compare.
Low Pass and High Pass Filters
I need to read Alex's document, but here are a couple of quick tricks you can try:
1) After performing the FFT, make a ROUND selection starting at the center.
2) Feather the selection. (try it with a large number and with a small number)
3) Press the Delete key. (This will make a high pass filter because we've just deleted the low frequencies)
4) Perform the inverse FFT
1) as before
2) as before (you might try a larger feather radius for this test)
3) Select Inverse (now the high frequencies are selected, not the lows in the center)
4) Press the Delete key. (This will make a low pass filter because we've just wiped out the high frequencies.)
5) Perform the inverse FFT
Notes: You can also try going into the QuickMask and making a radial gradient from the center as a method of proportionately selecting frequencies. If you have one that goes from 0 (not selected) in the center to 255 (fully selected) at the outer edge, you've created something very much like an "Ideal Inverse" and that can be useful for contrast adjustment.
You might also try using the Adjust->Levels function on a selection to increase/decrease the relative strength of a selection. By using Delete or Levels, you only affect the magnitude of a frequency. I would recommend AGAINST using the clone tool because then you're remapping stuff from another frequency and probably making extra junk in your image.
Time to read Alex's notes...
Yup.. He's using FFTW. There are license issues with that. I can't sell a product based on it. It is, however, extremely fast even with non-power-of-two dimensions.
Also, because the channels are only 8-bit (unless you're specifically choosing 16-bit) your image will get noiser just from the FFT->IFFT transform. Try it.
One of the things that we're going to have to decide here is what should be in a package that does FFTs. I don't want you guys to be paying $800 for something that you're going to use maybe 5 filters out of 177. That isn't cool. I would rather wrap some nice UI around the kinds of functions that you will do and make it part of Optipix ?4? ($150, but *discounted* to all of you.)
I do have ideas along those lines, but am reluctant to share them yet because they will influence your thinking and I'd like to see what y'all come up with.
I will also provide some FoveaPro serial numbers to this group because we cannot get very far in the discussion once your 3-week demo period has run out.
I did think once that I should fill with black, then I thunk again that this would be creating new noise - seeing as the original un-textured image would not have little black spots all over the FFT image. Maybe 50% grey? Dunno. In the end cloning (with blending set to Darken) seems the easiest way out.
In practical terms, again, FFT won't usually take out all the texture, and as Camaraken pointed out a little random fluctuation could throw off the FFT completely. So, after going through FFT an image will almost certainly need some more touching up.
What I have recommended has been to take out the worst of the texture with FFT and then use some more conventional techniques (as beautifully explained in Flora's tutorial) to finish up.
- Didn't know that 1023 factored easily! Oops!!
- I had tried manipulating the FFT space before, but always ended up with a semi-transparent gooey mess. Will try again.
- Is that really a ROUND selection? I had imagined that it would have to be oval, in the proportions of the canvas.
PS Now you've put up a photo, people are going to think we're brothers!
Last edited by byRo; 05-28-2005 at 08:18 AM. Reason: Karnt spel
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