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Old Apr 19, 2011, 1:55 PM   #1
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Default How can I extraxt IR data from RAW image ?

Hi
How can I filter only Infra Red image from RAW ?
I want to get IR image without IR filter

My camera is Panasonic FZ35

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Old Apr 20, 2011, 2:04 AM   #2
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Does Panasonic FZ35 stores IR data in RAW file ?

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Old Apr 20, 2011, 6:54 AM   #3
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Sorry, it doesn't work that way. Photosites on a sensor simply record values, based on how much light hits them while the shutter is open. Those values are then stored in the RAW file. It doesn't distinguish between different wavelengths, and most of the IR light spectrum is going to be cut out from reaching those photosites by a filter over the sensor anyway.

What does happen is that each photosite is only sensitive to one color (red, green or blue). That's because of the Bayer Filter array over the sensor. Then, the values are combined during raw conversion (based on values from adjacent pixels), so that Red, Green and Blue values are stored for each pixel location in the final image. See more about how that works here:

http://en.wikipedia.org/wiki/Demosaicing

But, again, most IR light is being filtered by an IR cut filter over the sensor. You can't get around that by shooting RAW, and there is no way for the RAW file to know what wavelength the light that reached it was at. It's only recording values for how much light it received at each photosite, not the wavelength of the light (it has no way to distinguish visible light from IR)

If you want to record IR images, you'll need a filter over your lens that blocks the visible spectrum and lets only IR through to the sensor. But, because modern digital cameras use an IR cut filter over the sensor, you'll need relatively long shutter speeds to get enough light through to record an image.
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Old Apr 21, 2011, 10:51 PM   #4
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In addition to what JimC said, some cameras have IR cut filters that are so efficient it becomes impractical to record an image. I discovered that yesterday while shooting two different cameras with a Hoya R72 filter.

The only other option would be to have the camera converted (they take out the filter over the sensor), but then its not useable for regular photographs.
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Old Apr 22, 2011, 2:37 AM   #5
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However, the FZ35/38 can definitely see some light that isn't visible to the human eye - I noticed that if I take a picture of my TV then it picks up coloured lights on the Wii controller that I can't see.

You could just take a regular RAW image, split it into RGB channels in photoshop. It wouldn't be true infra-red but the red channel on its own would give you a similar effect.
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