IR imaging, false color and image subtraction question

K
Posted By
KBob
Feb 28, 2004
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781
Replies
4
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Closed
Here’s what I’m trying to do: with two or more IR filters having different cutoffs (separate exposures for each), I’d like to subtract one image from the other to achieve a "passband" effect. Each of these filters pass IR below their cutoff points–for example 720nm and 1000nm. I’d like to be able to create a false color image of (for example) red, IR from 720 to 1000nm, and 1000nm and below, assigning each of these spectral regions to R, G and B. What is the best approach to this using Photoshop CS?
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J
john
Feb 28, 2004
In article , KBob
wrote:

Here’s what I’m trying to do: with two or more IR filters having different cutoffs (separate exposures for each), I’d like to subtract one image from the other to achieve a "passband" effect. Each of these filters pass IR below their cutoff points–for example 720nm and 1000nm. I’d like to be able to create a false color image of (for example) red, IR from 720 to 1000nm, and 1000nm and below, assigning each of these spectral regions to R, G and B. What is the best approach to this using Photoshop CS?

Are you using color IR or B&W IR film? Single exposures, or multiple frames with different exposures? (And I presume you are using Kokak HSI 4143 film, or some other that covers 1000nm.)
K
KBob
Feb 28, 2004
On Sat, 28 Feb 2004 11:39:36 -0600, (jjs)
wrote:

In article , KBob
wrote:

Here’s what I’m trying to do: with two or more IR filters having different cutoffs (separate exposures for each), I’d like to subtract one image from the other to achieve a "passband" effect. Each of these filters pass IR below their cutoff points–for example 720nm and 1000nm. I’d like to be able to create a false color image of (for example) red, IR from 720 to 1000nm, and 1000nm and below, assigning each of these spectral regions to R, G and B. What is the best approach to this using Photoshop CS?

Are you using color IR or B&W IR film? Single exposures, or multiple frames with different exposures? (And I presume you are using Kokak HSI 4143 film, or some other that covers 1000nm.)

I’m using a digital camera (Sony F828) that has plenty of sensitivity, even well below 1000nm. Usually the blue channel has the least noise, but I’m trying to take multiple exposures of the same scene with each of 2 or 3 filters, then subtract the image content between them in order to create a new color triad for producing a false color result. Since the camera has relatively high resolution and sensitivity, the results should be good, if only I could remember how it was done…
J
john
Feb 28, 2004
In article , KBob
wrote:

[…]
I’m using a digital camera (Sony F828) that has plenty of sensitivity, even well below 1000nm.

Excellent.

Usually the blue channel has the least noise,

I’ve found the Green (in RGB) to be cleanest with film, but moving on…

but I’m trying to take multiple exposures of the same scene with each of 2 or 3 filters, then subtract the image content between them in order to create a new color triad for producing a false color result.

Look into layer modes, and in particular the "apply image" option inPS. Check out Ed Scott’s good explanation at:
http://www.photo.net/photo/edscott/ms000010.htm

I’ll bet it rings all the familiar bells with you.

Since the camera has relatively high resolution and sensitivity, the results should be good, if only I could remember how it was done…

Should you ever have the opportunity – try Medium Format film, or even 4x5IR. You will be floored by the quaility.

Best of luck. Share images with us if you can.
K
KBob
Feb 28, 2004
Look into layer modes, and in particular the "apply image" option inPS. Check out Ed Scott’s good explanation at:
http://www.photo.net/photo/edscott/ms000010.htm

I’ll bet it rings all the familiar bells with you.

That certainly hits the nail on the head, doesn’t it? Thanks for the URL, and yes-I’ll be anxious to share my experiences with this method. Now…pray for sun (sorry, Seattle).

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