RP Tutorials - - I need help with the fft filter.

zeldakasumi · #1 06-26-2006, 12:11 AM

Hello! I am new here and have found this site to be extremely helpful.^^

I need to remove paper texture from some old photos and am trying to follow this tutorial http://retouchpro.com/tutorials/?m=show&id=185 but my red channel is coming out completely black after I run the first filter. Can anybody tell me why this is and what I should do? Here are the two photos I was testing it on link. Thank you very much!

Flora · #2 06-26-2006, 05:17 AM

Hi zeldakasumi,

welcome to RP!

... I don't really know why that happened ... but surely something went wrong along the way ..

What I can tell you to try is:

* Make sure you didn't jump any step of the procedure,

* Make sure you work on a flattened (background only) copy of your image.

* Make sure you are working in RGB Mode. (BTW are you using the RGB FFT?)

* Make sure you are working on the composite (RGB) image and not on a single Channel when giving both commands: the (RGB)FFT first and the (RGB)IFFT after darkening the stars...

Try again and let us know... I had a quick try at one of your pictures and it can be done very well ...

zeldakasumi · #3 06-26-2006, 07:56 PM

Thank you for answering!^-^

Um, I still can't get it to work for me. I am using the RGB FFT, a flattened image, etc. What happens when I run the filter is my red channel turns completely black, a texture without stars is on the green channel, and the blue channel is a solid 50% gray. When I run the IFFT filter without doing anything to the channels the image comes out completely black. I also tried using the stand alone program ImageJ and I do get a cross with stars then but when I run the IFFT process it comes out almost completely black with just the barest silhouette of the figures.

EDIT: I tried it again with the image resampled to 300dpi instead of a 600dpi, and it worked!

However, if I don't resample and change it to 300dpi it still doesn't work. I really want as much image information as I can get so I don't want to resample. How can I make this work?

amontiel69 · #4 06-26-2006, 10:12 PM

I just joined this forum today, so this is my first post. I was having the same problem the original poster had with my red channel coming out completely black and the blue channel coming out solid gray. Just like it happened to her, I was able to apply the filter when I resampled my image from 600 dpi to 300 dpi. So, apparently it only works with images set to that resolution. Unless I am doing something totally wrong here. Any comments?

Thank you

Alejandro

Flora · #5 06-27-2006, 12:48 AM

Hi,

Alejandro,

welcome to RP to you too!!

When I worked on zeldakasumi's picture yesterday, I hadn't changed the resolution (600 pixels/inch) ... but, for speeding up the process, I had reduced its size... and it worked perfectly ...

After reading Alejandro's post, I made a search in our Forums, and found this post dealing with the same problem ...

Apparently the plug-in doesn't like files over a certain size ... In the quotation Bmud says that he found that "3072 is the magic number" (as the larger side of the image I guess...) ... Well, I tried that size, and still had a black red channel... so, I resized to 3000 pixels ... still no go ... I then resized the image decreasing it of 5 pixels each go ... The biggest size accepted by the FFT plug-in was: 2980x2822 pixels at the scanned resolution of 600 pixels/inch.. (see attachment)

Hope this helps.

Cameraken · #6 06-27-2006, 03:10 AM

Hi.

I ran a similar test to Flora here
http://www.retouchpro.com/forums/image-help/12703-fft-black-canvas-baseball-card.html

So if you want to keep the highest resolution Image Analyser will do at least a 4000 x 4000 image.

It’s available here (and it’s a bit easier to use)
http://www.retouchpro.com/forums/software/7210-freeware-image-analyzer.html

Ken.

amontiel69 · #7 06-27-2006, 07:48 AM

Hello Flora and Cameraken,

After I posted my message, I continued to try experimenting with the filter (I don't give up too easily) and I started changing the dimensions instead of the resolution. I was not as granular as Flora was, changing by 5 pix every time, but I arrived at 3000 on the longest side and it worked at 600 dpi. I am now having the problem that even after carefully selecting every single white spot I can see on the red channel, it still leaves a lot of the paper texture all over the image's surface. Should I select only those that clearly look like "stars" (a bright central spot with a halo around it) or everything that is white on the image?

I will look at the software on the link Cameraken posted and see how that works

Thank you for your help.

byRo · #8 06-27-2006, 08:17 AM

Quote:

Originally Posted by amontiel69

Should I select only those that clearly look like "stars" (a bright central spot with a halo around it) or everything that is white on the image?

The stars really should look like stars, a bright central part with vertical / horizontal lines passing through.
The stars should also always be in some sort of regular array, so little white spots in strange places are not part of a regular texture.

Quote:

Originally Posted by amontiel69

......it still leaves a lot of the paper texture all over the image's surface.

Usually this is because there are some stars hidden in the white central vertical / horizontal axis. They are not easy to see but often by following the general pattern you can "guestimate" where the hidden star should be. Painting a few places on the central axis doesn't hurt much, just don't get close the big central star.

Rô

amontiel69 · #9 06-27-2006, 09:38 AM

Thank you very much for your reply. I will try again painting as you suggested. I downloaded the Image Analyzer and had a try there. Even though I do software for a living, the logic of the program just escapes me. I found your post regarding the FFT filter at http://www.retouchpro.com/forums/showthread.php?t=7210, but it is just not doing what I want it to do. Even though this program seems to be a real piece of art, it is going to require a lot of experimentation with it.

I go to Map -> Make Map -> Fourier Transform and after a while I get a black image with a large bright central area and just a few dots scattered around. I assume that the way to work with this is to then select the eraser and get rid of those dots, but pressing P does not let me preview nor pressing the up and down arrow changes the eraser size.

Oh well, the world of retouching teaches me something every day.

Alejandro

amontiel69 · #10 06-27-2006, 10:06 AM

Hello again,

I just tried using the FFT filter painting only on those spots that look like stars and I am attaching a closeup of the results so you can see what I get after running the filter. Any ideas?

Thank you for your time and help

Alejandro