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image mock-up
In message , fritz_2077
writes Hi, I have a requirement to mock up an image based on some MTF data that has been given to me. It sounds a bit like a homework or project problem. Though most university terms have just ended... In essence what I need to do is to take some imagery from an optical system that I know the MTF curve for, and change the imagery such that it looks similar to that produced by a modified version of the initital system. The latter MTF curve will be of a lower performance than the first so in practical terms I need to degrade the image. Can anybody recommend a way to do this? I am relatively new to optics so the principles are not 100% understood. My initial idea was to perform a FFT on the image and then adjust the magnitude values in some way before applying the inverse FFT. I'm not entirely sure how I would go about doing the adjustment to the magnitudes but any advice would be gratefully accepted. Thanks in advance. You will probably get more complete answers on sci.image.processing ps. Also if anyone know of any software that could help with this I'd appreciate knowing what it is and where it ca be obtained from. There are various ones around. Most accept an image and a point spread function in real space rather than the MTF. The standard way to do this sort of thing is with an FFT based convolution code. Some thought is needed about the edge discontinuities and other implementation details. Regards, -- Martin Brown |
#2
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image mock-up
In message , fritz_2077
writes Hi, I have a requirement to mock up an image based on some MTF data that has been given to me. It sounds a bit like a homework or project problem. Though most university terms have just ended... In essence what I need to do is to take some imagery from an optical system that I know the MTF curve for, and change the imagery such that it looks similar to that produced by a modified version of the initital system. The latter MTF curve will be of a lower performance than the first so in practical terms I need to degrade the image. Can anybody recommend a way to do this? I am relatively new to optics so the principles are not 100% understood. My initial idea was to perform a FFT on the image and then adjust the magnitude values in some way before applying the inverse FFT. I'm not entirely sure how I would go about doing the adjustment to the magnitudes but any advice would be gratefully accepted. Thanks in advance. You will probably get more complete answers on sci.image.processing ps. Also if anyone know of any software that could help with this I'd appreciate knowing what it is and where it ca be obtained from. There are various ones around. Most accept an image and a point spread function in real space rather than the MTF. The standard way to do this sort of thing is with an FFT based convolution code. Some thought is needed about the edge discontinuities and other implementation details. Regards, -- Martin Brown |
#3
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image mock-up
if u can FFT MTF and (TFF) then methinks u hav more skills than ur post
implies try www.adobe.com Artie "fritz_2077" wrote in message om... Hi, I have a requirement to mock up an image based on some MTF data that has been given to me. In essence what I need to do is to take some imagery from an optical system that I know the MTF curve for, and change the imagery such that it looks similar to that produced by a modified version of the initital system. The latter MTF curve will be of a lower performance than the first so in practical terms I need to degrade the image. Can anybody recommend a way to do this? I am relatively new to optics so the principles are not 100% understood. My initial idea was to perform a FFT on the image and then adjust the magnitude values in some way before applying the inverse FFT. I'm not entirely sure how I would go about doing the adjustment to the magnitudes but any advice would be gratefully accepted. Thanks in advance. Fritz ps. Also if anyone know of any software that could help with this I'd appreciate knowing what it is and where it ca be obtained from. |
#4
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image mock-up
"fritz_2077" wrote in message om... Hi, I have a requirement to mock up an image based on some MTF data that has been given to me. In essence what I need to do is to take some imagery from an optical system that I know the MTF curve for, and change the imagery such that it looks similar to that produced by a modified version of the initital system. The latter MTF curve will be of a lower performance than the first so in practical terms I need to degrade the image. Can anybody recommend a way to do this? I am relatively new to optics so the principles are not 100% understood. My initial idea was to perform a FFT on the image and then adjust the magnitude values in some way before applying the inverse FFT. I'm not entirely sure how I would go about doing the adjustment to the magnitudes but any advice would be gratefully accepted. Thanks in advance. Fritz ps. Also if anyone know of any software that could help with this I'd appreciate knowing what it is and where it ca be obtained from. I don't have a specific answer, but oyu may be able to find it more easily knowing that the process is called modulation. You are modulating an image according to the properties of the optical system. The reverse process, demodulation, is probably more common. |
#5
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image mock-up
"fritz_2077" wrote in message om... Hi, I have a requirement to mock up an image based on some MTF data that has been given to me. In essence what I need to do is to take some imagery from an optical system that I know the MTF curve for, and change the imagery such that it looks similar to that produced by a modified version of the initital system. The latter MTF curve will be of a lower performance than the first so in practical terms I need to degrade the image. Can anybody recommend a way to do this? I am relatively new to optics so the principles are not 100% understood. My initial idea was to perform a FFT on the image and then adjust the magnitude values in some way before applying the inverse FFT. I'm not entirely sure how I would go about doing the adjustment to the magnitudes but any advice would be gratefully accepted. Thanks in advance. Fritz ps. Also if anyone know of any software that could help with this I'd appreciate knowing what it is and where it ca be obtained from. Take a look at the excellent MTF tutorial he http://www.normankoren.com/Tutorials/MTF.html . It's not very mathematical, but it contains a wealth of general information that might give you some hints about how to proceed with your project. I'd be tempted to try a heuristic approach first, if only to get a ball-park idea: Take one of those perfect varable spatial-frequency lp charts and using Photoshop or similar, make a test page of strips at various referenced contrast levels, print it, then eyeball it for the degraded MTF you're looking for. Load your image, then adjust its contrast to the eyeballed reference level and Voila! you've got your result. Maybe. Hopefully. An FFT approach is outlined on the web site indicated above and is as follows: ---------------------------------------------------------------------------- ------------------ The response of a component or system to a signal in time or space can be calculated by the following procedure. 1. Convert the signal into frequency domain using a mathematical operation known as the Fourier transform, which is fast and easy to perform on modern computers using the FFT ( Fast Fourier Transform) algorithm. The result of the transform is called the frequency components or FFT of the signal. Images differ from time functions like sound in that they are two dimensional. Film has the same MTF in any direction, but not lenses. 2) Multiply the frequency components of the signal by the frequency response (or MTF) of the component or system. 3) Inverse transform the signal back into time or spatial domain. Doing this in time or spatial domain requires a cumbersome mathematical operation called convolution. If you try it, you'll know how the word "convoluted" originated. And you'll know for sure why frequency domain is widely appreciated. --Excerpted from Norman Koren's Photography Page, http://www.normankoren.com/Tutorials/MTF.html. ---------------------------------------------------------------- (I believe the quoted passage between the lines above constitutes "fair use" and apologize profusely if such is not the case. The work and text were produced by Norman Koren, NOT me.) In the dim, ancient past, in an age before the Great Neuron Depletion, I used Mathcad's FFT routines for such things. These days, "Fuh...Fuh....Tea!", is something I diffusely exclaim when I at last recognize the warm, welcoming beverage sitting in a cup on my tray at the rest home. :-) |
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