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Old Jan 5, 2016, 3:29 PM   #1
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Hi again,
Further to my question re how cameras produce black and white images. I have converted one of my old point and shoots (an EasyShare Z915) to IR, by removing it's IR blocking filter. Of course, what I have now is pictures with a pink cast, and colours. If I now switch the camera to black and white mode, I get what looks to me as a pure NIR image, i.e. green vegetation is white. Is this a true NIR image, or just some sort of adulterated black and white. The images look quite similar to what my Cybershot F717 (which is IR capable) produce. (The reason I converted the EasyShare is because the F717 is crippled in IR mode (wrt shutter speed), and cannot be used in full sunlight without filters that restrict the amount of light taken in.
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.... john
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Old Jan 5, 2016, 4:19 PM   #2
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If you have only removed the IR cut filter, I would think you would be getting a B&W image which includes both visible light, and IR. To get just the IR component, you would have to use a filter to block the visible spectrum.
As I recall, the sensitivity of silicon sensors is heavily biased toward the deep red and Infrared, which is part of the reason for the IR cut filters in the first place.
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Old Jan 6, 2016, 6:31 PM   #3
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Hi VTphotog,
So, what you're saying is that black and white images are basically modified coloured images; not coloured images minus colour, which is what IR is. Would that be another way of putting it?
..... john
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Old Jan 6, 2016, 10:03 PM   #4
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Originally Posted by Shinnen View Post
Hi VTphotog,
So, what you're saying is that black and white images are basically modified coloured images; not coloured images minus colour, which is what IR is. Would that be another way of putting it?
..... john
Is that what I'm saying? I'm not really sure.
The IR images I have seen have been either from thermal imaging cameras, IR film (with IR filter on the lens), or digital cameras with IR filter on the lens. The images were more or less as you describe your pics; with bright foliage and dark, nearly black skies. The TI cameras had cooling systems to keep the CCD at a constant, (very cold) temperature, so temperature of picture elements would correspond to calibrated brightness levels.
Infrared LEDs as used in remote controls, should show up bright white, as would incandescent lamps, but fluorescent lights would be bright only at the ends where the heaters are.
Not sure about the white LED types, but would guess they would not be bright, if visible at all.
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Old Jan 9, 2016, 10:00 PM   #5
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Hi,
I'm at an impasse here. I've abandoned using Black and white settings on the IR converted camera. They're very noisy and course looking; so I think this is a dead end. I've converted two cameras now (i.e removed the IR cut filters) and each gives me an image that is a combination of IR and colour, with a magenta like hue. I haven't figured out how to remove the hue and the colours. These are point and shoots, and are not amenable to filters. I'm going to have another look at my F717 and see if I can adpapt it (add filters) so that it will give me a pure NIR image.
Thanks,
...... john
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Old Jan 10, 2016, 8:34 AM   #6
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If you only removed the IR Blocking filter, you still wouldn't get much IR because the green and blue filters in the Bayer Filter would still be blocking IR, and the resulting images wouldn't look much different than if you hadn't removed the IR Blocking filter.

If, however, you removed the Bayer Filter as well as the IR Blocking Filter, the camera would process the resulting images as though the Bayer Filter were still in place, except that the images would be brighter. That is, the photoreceptors that were previously under the blue filters in the Bayer Filter and only detected blue light, would now be receiving the entire spectrum of light, the photoreceptors that were under the green filters would be receiving all light instead of just green light, etc. So each photoreceptor would detect about 3 times as much light as it did before you removed the Bayer Filter, but in addition, the camera would try to make sense out of the extra light it was receiving, and would produce images that were very bright, possibly with a slight tint depending on which if any color was predominant in the scene you shot.

In other words, I don't think that simply removing one or more filters from the sensor would actually provide you with an IR image, even if you added an IR Passing filter (a photographic filter that passes IR Light but blocks all colors of visible light), because the camera would still think that the light detected by the sensor was passing through the Bayer Filter, and thus would still contain all colors of visible light, and would process the image as if it did, but with anything green, vegetation or not, being brighter.

So if the scene contained a lot of green vegetation, and you didn't use an IR Passing filter, the vegetation would still appear brighter because Bayer Filters have twice as many green photoreceptors than either red or blue, so it wouldn't actually be an IR image, because the camera wouldn't understand the data it was receiving from the sensor, and would process the image the way it would normally.

So if you're not using an IR Passing Filter, you're not getting IR images. And in order to get a true IR image, you'd have to reprogram the camera so that it would stop thinking it still had the Bayer Filter installed.

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Old Jan 10, 2016, 11:33 AM   #7
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Some of our users here have done IR work with DSLRs. Due the the amount of light blocked by the IR filters used, these tend to be long exposures even in daylight. Try searching the forums for IR or infrared pictures to get an idea. I think there has been some discussion of techniques in these threads.
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Old Jan 10, 2016, 11:35 AM   #8
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If you want to confirm that you're taking IR photos, take a photo in the dark. Warmer objects (people, animals, portions of a dark house where heat is escaping, etc.) will be brighter than the cooler background.
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Old Jan 10, 2016, 1:36 PM   #9
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Well, I don't seem to get any results using the search terms I mentioned for these forums. Off the top of my head, I recall that forum member Mtngal has done some IR, so that may be a place to start looking.
I believe the type of IR photos Tcav is talking about are what one would get with the thermal imaging cameras, and include far infrared. Using near IR filters with a digital camera (which is what you will normally get) won't quite give you the same results, though a lighted cigarette will show up brighter than a fluorescent lamp (for example)
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Old Jan 10, 2016, 3:20 PM   #10
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https://en.wikipedia.org/wiki/Infrared_photography

If you remove both the IR Blocking Filter AND the Bayer Filter, and use an IR Passing filter, you'll be doing IR Photography. There are two kinds of IR Passing Filters: one appears black because it blocks all visible light while only passing IR, and the other passes IR and some red light so you can just barely see through it.

You're not doing IR photography if you just remove the IR blocking filter, or you remove the IR filter and the Bayer Filter but don't use an IR Passing Filter.

But the camera will still produce color images because it will still presume that the Bayer Filter is in place and providing color information. Converting the images to B&W will get rid of the false color.
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