Image Processing techniques to remove diffraction Artifacts

Ashill Chiranjan

I am trying to create a programmable aperture using a DLP but due to the nature of the application I appear to get lots of diffraction artifacts in my images (see attached).

Are there any image processing techniques that I can use to remove these artifacts. i.e. post processing techniques.

In the images below we see a picture of a dot. Only 1 dot is being photographed (bottom right) but 3 other dots appear around it. Can this be removed post processing?

It was suggested to Use 2D FIR filters. Not sure if any other techniques are possible?

over 9 years ago

0 Fizix over 9 years ago

TI__Guru 54725 points

Hello Ashill,

Are you using any imaging lens to form the image?

Using an imaging lens just as you would with a broad band illumination to form the image will also re-converge the image of the dot into one.

Fizix

0 Ashill Chiranjan over 9 years ago in reply to Fizix

Prodigy 90 points

Hi

Yes i am using an imaging lens to form the image.

0 Fizix over 9 years ago in reply to Ashill Chiranjan

TI__Guru 54725 points

Hello again Ashill,

Thank you. Would it be possible to make a simple diagram of your optical system from illumination source to image? It would be helpful.

Fizix

0 Ashill Chiranjan over 9 years ago in reply to Fizix

Prodigy 90 points

0 Ashill Chiranjan over 9 years ago in reply to Ashill Chiranjan

Prodigy 90 points

Hi fizix

Please see diagram above. Sometimes if the object is far enough away the light is already collimated so i do omit lens 1. The objective is basically to get the dlp into the aperture plane.

Thank you

0 DLP_ViALUX over 9 years ago in reply to Ashill Chiranjan

Prodigy 30 points

Hi,

Things will become more simple if you place the DMD plane parallel to the image plane.

If that is not feasible for certain reasons, you shall take advantage of the https://en.wikipedia.org/wiki/Scheimpflug_principle

0 Fizix over 9 years ago in reply to Ashill Chiranjan

TI__Guru 54725 points

Ashill,

Your arrangement shows the DMD in collimated space which puts the DMD surface at a Fourier transform plane of the object. This WILL give you diffraction artifacts. I know of no way to remove them in this scheme.

Here is what I was implying (see diagram):

Of course this may defeat what you are attempting to do. Otherwise you will have to move far enough away from the DMD that you isolate only one order in your current configuration. Specifically only one order gets into the lens or you put an aperture on the outbound lens to only capture one order.

I hope this helps.

P.S. To DLP_ViALUX - I think his diagram was not intended to represent relative parallel surfaces. In any case Sheimpflug will not solve the diffraction artifacts if the DMD is in collimated space.

0 Ashill Chiranjan over 9 years ago in reply to Fizix

Prodigy 90 points

Hi Fizix

Thank you very much for the reply and diagram. I really appreciate it.

With regards to the configuration you suggested, yes it is defeating the purpose of my application as I do not wish to form an image on the DLP. I have been told that the only way to remove the diffraction is post processing techniques such as FIR filters. Is there any other way using image processing techniques that I can use to remove the artifacts.

0 Fizix over 9 years ago in reply to Ashill Chiranjan

TI__Guru 54725 points

Hello Ashill,

I am not aware of any post processing techniques to do it, but that does not mean they do not exist.

Is using an iris at the second lens to restrict the rays to those only from the brightest order not an option?

Fizix

0 Ashill Chiranjan over 9 years ago in reply to Fizix

Prodigy 90 points

Hi Fizix

It most certainly is an option. I just wanted to check if other post processing techniques exist before i introduce another aperture into the system. Hopefully that is able to help with the diffraction effects.

Regards

Ashill

0 Fizix over 9 years ago in reply to Ashill Chiranjan

TI__Guru 54725 points

Ashill,

I am not aware of any post processing techniques, but you may want to search some of the literature from the MOEMS conferences at SPIE. And other research done on DMDs.

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Image Processing techniques to remove diffraction Artifacts