Using the FFT filter to remove photgraphic paper texture

[bart_hickman]

Seems like just using the median filter (bare minimum needed to soften the pattern), followed by a good NR tool (Neat Image, Paintshop Pro, etc...) seems to work pretty well for that. Sometimes those magazine patterns are very irregular--the FFT will have a ton of harmonics and thus be time-consuming.

Bart

[Bmud]

I found today that FFT really is just fine the original way we were doing it with the FFT and median filter. I split a 600dpi image up today and did the CMYK channels seperately only to find that it comes out more harsh and messes up the colors -- so I had to use a median layer to correct color anyway.

Maybe the trick to getting color halftone removal to look better is redesigning a brush with a linear gradient to help with the circles of different sizes.

I agree though. this i all very fascinating, but I'm about fed up with the work involved. A full blown pattern removal filter would be nice.

If this discussion got any more technical we'd have enough to figure it out ourselves :P

[Taco]

Originally Posted by bart_hickman

Seems like just using the median filter (bare minimum needed to soften the pattern), followed by a good NR tool (Neat Image, Paintshop Pro, etc...) seems to work pretty well for that. Sometimes those magazine patterns are very irregular--the FFT will have a ton of harmonics and thus be time-consuming.

Bart

I've been doing the median filter/noise reduction for a while and it's pretty good. As well as scanning at 600 dpi and reducing to 300 dpi. but I'm always on the look out for something better.

[Bmud]

More recently, with pictures that are big enough, I've just been running the despeckle filter to kill halftone patterns.

[Taco]

not a big fan of despeckle myself, but the new noise reduction filter in psp X has a lot of potential. A friend of mine swears by it to remove the regular pattern without harming the detail. I can't match the results yet unfortunately, but I'm still playing around with it.

Anyway, didn't mean to get this subject off topic. I'm still interested in an automated fft filter such as this. I set up a script is psp that uses the poster filter (set to 4) and then the threshold filter (set to 152) to seperate the brighter stars from the darker background. cut out the center, then color it gray, overlay it to a copy of the fft image and use ifft. the results work and are pretty quick, but it could be very much improved. I left out a lot of details, but it was just something I was toying with.

[bart_hickman]

Here's a handy script I use to split the active layer into RGB components so I can edit them directly. For the FFT, you can paint on the red layer. When you're done, just merge the group and you're ready for the IFFT. The colors are put into groups so it's very easy to quickly add a curve to the red channel to make the stars more vivid while you erase them. Just delete or turn off the added layers prior to merging the RGB group.

In PSPX, it can run in the restricted folder. It won't run in PSP9 or earlier yet--I have that on my to-do list.

http://home.comcast.net/~zumbari/Scr...pRGB.PspScript

Bart

[Bmud]

I just recently found the magic of the new Reduce Noise filter circa Photoshop CS2. I havn't run FFT in quite a while.

[bart_hickman]

Hi Klassy,

Is there a chance you used the wrong FFT? There are two FFT plugins--you want to use the RGB FFT. Which image did you do the FFT on? Can you post the result of the FFT?

Bart

[bart_hickman]

Your attached image is too small for me to see the texture. Could you post either a larger size or a link to the original?

Bart

[bart_hickman]

The FFT technique works on pattern noise. Pattern noise is concentrated at a few discrete frequencies so when you do a Fourier transform on the image, the pattern noise shows up as a star pattern--the stars are the frequency-domain representation of the noise. (The technical term for noise like this is spurious noise and the stars are called spurs.)

In the image you attached, it looks like a combination of aliasing (due to image size reduction) and jpeg compression has caused the pattern noise to be converted into essentially random noise and thus no longer removable with the FFT.

If you have textured photos, you want to be sure to scan at a high enough resolution to not just capture the image details, but capture the details of the texture as well.

Bart

[videosean]

Originally Posted by Bmud

Apparently the plugin doesn't like images over a certain size. I've been trying to pinpoint the behavior as to reverse engineer some sizing rules or to make a proper bug report, but FFT i so slow while I'm at work that I'm having no luck even with a binary method. Just losing lots of time on the clock. It might also be a RAM problem.

Somewhere around the thus far, i've gotten..

bigger than 2662x2991
smaller than 2862x3191

I'm guessing that this means that 1024*3 = 3072 is the magic number. I'll do some more tests at home with my dual core and 2gb of RAM and see if I get similar results. I've got a 512 stick here.

Your post is getting close to what my problem has been I think. I have a scanned image that is 2878x3996 and I get a Red channel that is nothing but black (flat, 0 grey value) after running FFT-RGB and a Green channel with alot of noise and a cross pattern but no stars and the Blue channel is a flat 128 grey value.

I resized my image so that it was 2253 x 3072 (using your 3072 as the largest dimension - I had also added a 50% grey border before downsizing as per other user tips in this thread) and got the results I was expecting... stars and whatnot For a free filter I guess this is acceptable. The texture I'm trying to remove is a fairly typical mid to late 1970's matte paper surface from a portrait studio. The color in the image is completely faded/shifted to red/orange and there isn't any kind of watermark on the back of the print nor a studio's name on the front.

edit - because I'm lazy, I used the magic wand to select all the stars for fixing.

1. Magic wand tolerance = 8, uncheck contiguous, click in the middle of a star to select the brightest point.
2. Use the lasso tool, deselect all the areas you don't wish to correct - the large cross, for example, I deselected as well as a few small points that didn't look like stars.
3. Select -> modify -> expand by 5 pixels
4. Image -> Adjust -> Brightness/Contrast, I just reduced the contrast all the way down and the made a slight adjustment to the brightness so it looked like it matched.

This image has been a personal project that I've left sitting on my HD (it's been maybe 2 years since I scanned this image LOL) waiting for the day I found a good way to kill the paper's texture. Thanks RetouchPro and Alex

[sattva]

Originally Posted by Taco

I've searched for a while for something that would remove the moire (or halftone dot) pattern that is found in magazine prints. ... I'd like to apply filter and process complete. I wouldn't hesitate to pay for a commercial version if this were the case.

Taco,
There are a special Descreen filter to eliminate the halftone dots (the screen) and prevent the moire pattern:
http://www.descreen.net/eng/soft/descreen/descreen.htm
This plug-in employs the FFT.

Attachments:
1) The original image.
2) The same image after screen removing. You may see the prominent halftone moire pattern.
3) The same image after screen removing and moire reducing.

[chiko321]

I had come across another technique to remove the texture if you are having trouble getting software to work. It is quite simple. If you think of the texture that you see as a result of shadows and highlights on what is basically glossy paper, all you need to do is 1 of 2 things. Get a scanner that has dual bulbs, that is to say, one before and after the scanning head. If you can't find a scanner with dual bulbs, you can also do a neat trick by scanning the photo upright and then scanning the photo again (precisely 180 degrees) and scanning the "shadows and highlights" in reverse. Once the 2nd scan is rotated upright and aligned to the first scan at 50% transparency, pretty much all of the texture can be eliminated. This works best if your scanner head does not have any problems with variable skewing, otherwise you'll be "fudging" and stretching different zones of the photo to blend well with the first scan. In the meantime i'll definitely be looking into this other app as time allows! It could be a great timesaver! Especially if you know how to create actions or JSX scripts for CS3!

[oppor2nity]

First of all, thanks for posting this tutorial, as it seemed to be the solution to my current problem, and most likely will be. Alas, right now I cannot make this work.

No matter how I try, I can't achieve the final result as shown in the tutorial.

I'm starting out with an RGB8 scan which is yellow-ish as has a heavy embossed dot pattern all over the image. I have also tried desaturating this first, but that hasn't changed anything.

I copy, apply FFT, select the red channel only, see the stars and paint them out. I apply IFFT and end up with an image in which the pattern seems to be not gone, but more like cancelled out. The problem is, it resembles a negative. I drag that over the original and change the blending mode to Luminosity, but no colour can be seen through the greyish layer.

Where am I going wrong?

Cheers,

/Ulf

[chillin]

You could use ImageJ instead. It requires less steps.