HDR with Photoshop CS2

Discussion in 'Digital Photography' started by jdl8422, Sep 28, 2006.

  1. jdl8422 macrumors 6502

    jdl8422

    Joined:
    Jul 5, 2006
    Location:
    Louisiana
    #1
    I have been experimenting with trying to take some HDR pics. I have a canon 10D. The camera can be set to take 3 bracket exposures. I set it for -2..0..+2. I thought this would be enought for a HDR in CS2, but when I tell it to merge to HDR it says not enough dynamic range. Am I doing something wrong?
     
  2. spicyapple macrumors 68000

    spicyapple

    Joined:
    Jul 20, 2006
    #2
    I found it easier to shoot one exposure in RAW and use Photomatix (trial software) to create the HDR. It's faster and with better results. CS2 HDR isn't really that great.
     
  3. jdl8422 thread starter macrumors 6502

    jdl8422

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    #3
    What limitations do you have with the trial. Is it just good for a certain period of time?
     
  4. spicyapple macrumors 68000

    spicyapple

    Joined:
    Jul 20, 2006
    #4
    The trial software watermarks the images and runs indefinitely. There's really no need to bracket +/- 2 stops because the RAW format has 12-14 bits of dynamic range, which covers the bracketed exposure ranges.
     
  5. Zeke macrumors 6502

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    Oct 5, 2002
    Location:
    Greenville, SC
    #5
    Umm...HDR is 32 bits and raw dynamic range (expressed in bit depth) is about 9. There is no way you can say a single raw file = HDR. It's just not true. The idea behind HDR is that you can capture the detail in highlights and shadows by exposing for them and combining.

    As for the original question, I've never had the problem you describe. I routinely combine images of -2/-1/0 stops. Photoshop will let you merge to HDR any images that are varied (as far as I know) so you could technically use images 1/3 of a stop apart. If you post your images I could try it out and see if it's just something you're doing wrong.

    I don't like Photomatix as it looks chintzy and fake when you're done...the Photoshop method at least lets you control stuff and turns out very nicely when finished.
     
  6. Zeke macrumors 6502

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    Greenville, SC
    #6
    I find it somewhat confusing to talk about dynamic range in bit depth though since HDR is a floating point 32bit whereas images we traditionally deal with are integer. It's a lot easier to deal with f-stops. I think raw is about 10 stops from black to white. Obviously, the blacks are going to be noisy if you try and get any detail and most detail in the whites is lost due to the linear response of the sensors. This is why HDR was developed, so you can save the detail and make the dynamic range of your image as large as you want (depending on how many stops you expose for).

    Sorry for the rambling, I'm going to bed now.
     
  7. ChrisA macrumors G4

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    Jan 5, 2006
    Location:
    Redondo Beach, California
    #7
    One exposure does not really "count" as High Dynamic Range. Well OK technically it is the degenerate case of HDR just the same way that geometrically a point is a circle of zero radius. The whole point of HDR is to make an image that can't otherwise be captued in one expose
     
  8. ChrisA macrumors G4

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    Jan 5, 2006
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    Redondo Beach, California
    #8
    It's easy: one bit equals one f-stop. For example assume a 4-bit monochrome image. The shades of gray would be represented with numbers in the range 0...15 but lets call them 1...16. 1 is four stops less then 16. (each stop is a doubling of the amount of light, double 1 four times and you have 16)

    But notice the other problem with the 4-bit image. while it can hold four stops of dynamic range the grey scale is in one stop steps. You can trade dynamic range for smaler steps. For example with an 8-bit image you can store 8 stops of dymanic range but with one stop "steps" or you can have 6 stops of range with 1/4th stop steps.

    Let's say you want 12 f-stops of dynamic range and 1/8th stop steps. thats 12+3 bits, you would need 15 bits to do this and a 16-bit tiff file would work fine.

    I think you are right about RAW being about 10 f-stops. Typically RAW is 12 bits. But RAW files do not contain pixels and must be interpolated into images so the end result will have some bits to the right of the binary point if you are using fixed point math
     
  9. Zeke macrumors 6502

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    Oct 5, 2002
    Location:
    Greenville, SC
    #9
    Thanks for the explanation. It is very easy...I just didn't take the time to think about it. Yeah, I see the main benefit of using HDR is that it uses a floating point system (at least until you convert) that allows the steps between intensity values to vary by near infinitely small gradations prior to converting down (so you can get the levels of different sections correct before downconverting to 16bit).

    In any case, HDR is cool and requires more than 1 image for real HDR. 3 should be fine and I've done it with 1 stop between each exposure. I wish my camera would do more than 3 images in a bracket so I could just click 9 off and get the full range of the scene.

     

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