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Infrared filter on RGB image

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Infrared filter on RGB image

nisha
3 posts
Dear ImageJ Experts,

If I have sent this message twice please pardon me, because my first post
has "This post has NOT been accepted by the mailing list yet." on the top.

I want to apply an IR filter on a color image. And so was exploring
different tools to accomplish this task. I am new to ImageJ and have very
less knowledge about the programming possibilities.

I would like to know whether it is possible to apply an IR filter of a
specific wavelength on a RGB image or some other desired wavelength filter
(from the visible spectrum) on a RGB image? If so, please guide me.

Thanks in advance! :)

Best Regards,
Nisha

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Re: Infrared filter on RGB image

Robert Baer
88 posts
On 1/14/2013 11:40 AM, Nisha Shah wrote:

> Dear ImageJ Experts,
>
> If I have sent this message twice please pardon me, because my first post
> has "This post has NOT been accepted by the mailing list yet." on the top.
>
> I want to apply an IR filter on a color image. And so was exploring
> different tools to accomplish this task. I am new to ImageJ and have very
> less knowledge about the programming possibilities.
>
> I would like to know whether it is possible to apply an IR filter of a
> specific wavelength on a RGB image or some other desired wavelength filter
> (from the visible spectrum) on a RGB image? If so, please guide me.
>
> Thanks in advance! :)
>
> Best Regards,
> Nisha
>
> --
> ImageJ mailing list: http://imagej.nih.gov/ij/list.html
First, this is a more complicated question than I think you probably
appreciate.   Second, filtering, per se,  is typically done at capture
time using "hardware" filters.  You can do some "software filtering"
when you have extremely well defined spectral conditions, but this is
rarely the case.  Finally, there is the mixed situation where you want
to use multiple images with and without a hardware filter to separate a
part of a signal.  ImageJ has utility in this latter instance.

Digital RGB representations of images are typical done either by using a
monochrome camera taking pictures using a spectral filter placed in
front of the camera to limit the wavelengths captured, or by using a
color camera in which case the channels are most often separated by what
is know as a Bayer filter.  The spectral sensitivity of the monochrome
chip can vary in either case.

Some cameras have the ability to turn on and turn off an "IR " filter,
and if you have such a camera, you might be able to determine the IR
contribution to the image by image subtraction. ImageJ could help you
with this task depending on whether the IR filter is a lowpass or
bandpass filter.  ImageJ certainly can do mathematical operations on
sets of images like image subtractions.

You do not tell us enough about the hardware part of your task to tell
you much more about how ImageJ might help.

Rob Baer

--
__________________
Robert W. Baer, Ph.D.
Professor of Physiology
Kirksille College of Osteopathic Medicine
A. T. Still University of Health Sciences
Kirksville, MO 63501 USA

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Re: Infrared filter on RGB image

nisha
3 posts
Dear Dr. Baer,

I am extremely sorry, I made a huge mistake in explaining my doubt. Actually, I have a color image (captured from an ordinary camera) on which I want to produce an effect as if during the time of capture, the object was exposed to some wavelength. For example, while capturing an image, say the object was exposed with a wavelength of 630nm (red color) or an infrared wavelength.

I want to induce such effects on images. I am really sorry, I used wrong words in expressing my doubt.

Thanks in advance!

Nisha
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Re: Infrared filter on RGB image

Gabriel Landini
1783 posts
On Monday 14 Jan 2013 18:36:39 you wrote:
> Actually, I have a color image (captured from an ordinary camera) on which I
> want to produce an effect as if during the time of capture, the object was
> exposed to some wavelength.

No you can't achieve that on an image that has already been captured because
you do not know which parts of the image reflect or absorb IR light.

Digital cameras typically have an infrared blocking filter because the sensors
usually respond to the near infrared as well as in the visible spectrum. That
being said, a tiny amount of near infrared light gets in the camera and gets
mixed with the visible light, and this can be captured if you use a visible
light blocking filter like the Hoya R72 or the Wratten 89B (you can get these
filters in photographic equipment shops). But you can't really separate the
NIR light from the rest of the image once it is shot.

Some people remove the IR blocking filter from the camera to have more
sensitivity in the NIR, but this is not something you may want to do with an
expensive camera. With some webcams this can be done very easily.
See for example: http://www.hoagieshouse.com/IR/

Regards
Gabriel

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Re: Infrared filter on RGB image

Robert Baer
88 posts
In reply to this post by nisha
On 1/14/2013 12:36 PM, nisha wrote:

> Dear Dr. Baer,
>
> I am extremely sorry, I made a huge mistake in explaining my doubt.
> Actually, I have a color image (captured from an ordinary camera) on which I
> want to produce an effect as if during the time of capture, the object was
> exposed to some wavelength. For example, while capturing an image, say the
> object was exposed with a wavelength of 630nm (red color) or an infrared
> wavelength.
>
> I want to induce such effects on images. I am really sorry, I used wrong
> words in expressing my doubt.
>
> Thanks in advance!
>
> Nisha
>
>
Perhaps I am still missing your question, but let me try saying it this
way.  In "theory" an RGB color image contains only information from the
visible part of the spectrum and NO information about infrared
emission.  Depending on the physical collection method, however, this
theoretical assumption may not be the case.  I imagine you are concerned
that your images contain influence from IR emissions.

However, you can not estimate how much IR contamination there is in your
images  with software alone (ImageJ or any other software).  To estimate
IR contamination you must also make direct, physical measurement of IR
cross-talk under conditions where there is no primary image signal .  
Such crosstalk may vary with conditions (say excitation intensity), and
so it must be measured under conditions appropriate to you measure.  
That is, you need appropriate positive and negative controls for IR
crosstalk.

The only way to know how much contamination of your images comes from IR
emissions is to measure IR crosstalk physically.  If you construct some
sort of library specifying how much IR emissions affects each of your
RGB channels, you may THEN be able to subtract out its effect.

You CANNOT estimate how much IR has contributed to your sample images
from just the images.

Hope this makes the issue more clear,

Rob Baer

--
__________________
Robert W. Baer, Ph.D.
Professor of Physiology
Kirksille College of Osteopathic Medicine
A. T. Still University of Health Sciences
Kirksville, MO 63501 USA

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ImageJ mailing list: http://imagej.nih.gov/ij/list.html