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  1. #21
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    Maybe if the Adox/Fotoimpex plans to do small production runs of products equivalent to certain Agfa ones proves to be a technical and commercial success, that type of small scale low fixed costs method of manufacturing might one day allow someone to make colour infra red film. Well, it's a nice thought!

  2. #22
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    Quote Originally Posted by Helen B View Post
    I guess there is, but it depends on what properties you want to be equivalent. In many ways digital is a lot more suitable for false-colour infrared imaging than film is, particularly in technical applications.

    Best,
    Helen
    Helen;

    Digital cannot and does not do false color imaging. EIR does because the sensitivities are shifted and you use the filter to eliminate any blue portion of the spectrum.

    Digital retains its normal sensitivity in all cases, but merely imposes an infra red component on the image.

    PE

  3. #23
    AgX
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    There are multispectral cameras with separate spectral channels, especially for aerial surveying. I guess Helen was referring to those.

  4. #24

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    Quote Originally Posted by Photo Engineer View Post
    Helen;

    Digital cannot and does not do false color imaging. EIR does because the sensitivities are shifted and you use the filter to eliminate any blue portion of the spectrum.

    Digital retains its normal sensitivity in all cases, but merely imposes an infra red component on the image.

    PE
    Dear PE,

    Yes, but surely you can reassign any group of wavelengths to any colour in the image as presented, and filter out any group or groups. Or am I missing something? (It's late and this is far from impossible).

    Cheers,

    Roger

  5. #25
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    Roger, in digital, the blue is blue and IR sensitive, the green is green and IR sensitive and the red is red + IR. In film, the blue is blue + green, the green is blue + red, and the red is IR.

    I'm not sure how you would accomplish this feat in digital then, due to the sensitivity SHIFT in analog. Oh, you might approach it in PS, but nothing like in film. It would take massive manipulation in PS to do it which defeats the purpose of just clicking a shutter with analog.

    PE

  6. #26
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    Quote Originally Posted by Photo Engineer View Post
    Roger, in digital, the blue is blue and IR sensitive, the green is green and IR sensitive and the red is red + IR. In film, the blue is blue + green, the green is blue + red, and the red is IR.

    I'm not sure how you would accomplish this feat in digital then, due to the sensitivity SHIFT in analog. Oh, you might approach it in PS, but nothing like in film. It would take massive manipulation in PS to do it which defeats the purpose of just clicking a shutter with analog.

    PE
    PE,

    Taking Roger's post one step further:

    With false-colour film you normally use a yellow filter to restrict the blue+IR sensitive layer (which ends up as a red image) to just IR (or very near IR to be more precise). If you did the same with digital, then you would have IR, green+IR and red+IR. It is a trivial matter to turn that into IR, green and red channels, and you can assign any colour you wish to any channel - such as red for the IR channel, blue for the green channel and green for the red channel (to mimic EIR's false colours). This is not 'massive manipulation' by any means. Furthermore, you could use other filters or combinations of filters to produce any combination of three channels from five bands (very near UV, blue, green, red and very near IR).

    For those who don't already know, EIR has the following false colour effect:

    Blue + IR sensitive layer, forming a red image;
    Blue + green sensitive layer, forming a blue image;
    Blue + red sensitive layer, forming a green image.

    Best,
    Helen

  7. #27
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    Helen;

    I would put it this way.

    Remember that Blue is filtered out in the exposure

    Film:

    Blue + IR sensitive layer forms a cyan image of the IR light
    Blue + green sensitive layer forms a yellow image of blue light
    Blue + red sensitive layer forms a magenta image of red light

    Digital:

    Blue + IR sensitive layer forms a yellow image of IR light
    Blue + green sensitive layer forms a magenta image of IR light + green light
    Blue + red sensitive layer forms a cyan image of IR light + red light

    In the analog case then, the layers have only one sensitivity, but with digital two layers have IR + color sensitivity. Therefore in the analog film each layer is limited to 'seeing' one color but in digital the sensors can see 2 colors.

    That is the problem. And it is not trivial to separate. Although you can get some interesting looking pictures.

    PE

  8. #28
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    Quote Originally Posted by Photo Engineer View Post
    Helen;

    I would put it this way.

    Remember that Blue is filtered out in the exposure

    Film:

    Blue + IR sensitive layer forms a cyan image of the IR light
    Blue + green sensitive layer forms a yellow image of blue light
    Blue + red sensitive layer forms a magenta image of red light

    Digital:

    Blue + IR sensitive layer forms a yellow image of IR light
    Blue + green sensitive layer forms a magenta image of IR light + green light
    Blue + red sensitive layer forms a cyan image of IR light + red light

    ...
    PE,

    I think that you have a few things mixed up there in the digital part, and a typo in the film part*, but as this is APUG the best thing to do is probably to leave the digital discussion here (though I didn't start it) and let the readers decide who they want to believe.

    Best,
    Helen

    *"Blue + green sensitive layer forms a yellow image of blue light" should be "Blue + green sensitive layer forms a yellow image of green light". The transposition of cyan/red; yellow/blue; and magenta/green in our descriptions are just different ways of describing the same thing, of course - as it is a reversal film I gave the primary-primary connection. We are, therefore, in full agreement about the way EIR interprets colours and IR.
    Last edited by Helen B; 07-18-2007 at 07:14 AM. Click to view previous post history.

  9. #29
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    Helen, thanks for catching my error in the analog part. Your correction is 'correct' for analog.

    I did wish to describe analog in terms of the dye formed. I then described the digital in the same terms even though it does not form dye. I got the information for digital from the web sites devoted to this topic and some practical experiments.

    By using a very heavy neutral density over the lens of a digital camera, and then exposing, you can equalize the IR speed to the visible speed of the sensors thereby getting usable pictures as I described with color superimposed on the IR image.

    I have done quite a bit of this, but will not post it due to the fact that it is a digital work. I was trying to find a substitute for Infra Red color and could not, to my satisfaction, do this.

    PE

  10. #30

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    Quote Originally Posted by ajuk View Post
    The thing with colour infrared film is there is no digital equivalent is there?
    There is (NIK software), but it's not a very convincing imitation, AFAIC...as is usually the case with digital versions of film styles.

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