What exactly is HDR?

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This topic contains 5 replies, has 5 voices, and was last updated by  dangerdizzy 11 years, 9 months ago.

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  • #1010

    Jakevol2
    Participant

    I know it stands for High Dynamic Range. But what does that mean. I asked a person at work who has a Masters in Photography and she didn’t even know the term. I have seen examples of HDR photography but I still dont understand in essence what it is.

    #11842

    Snug Tight
    Participant

    Digital photography doesn’t have a very big dynamic range. If you take a photo with bright areas and dark areas in the same frame, the exposure will be set for one or the other. The bright area will look ok, but the dark areas will be too dark, or the dark will come out ok, but the bright areas will be washed out. With HDR, many shots are taken with different exposures of the same subject. Using a photo processing program, the photos are combined. It is probably explained better here:

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

    #11843

    Analogy
    Participant

    Dynamic range means the ability of an imaging device to capture extreme differences in brightness within a scene. You may have already noticed that your camera sees a scene a lot differently than your eye. While your eye can perceive detail in both the bright areas and shadows within the same scene, your camera might end up blowing up the bright areas to get shadow detail or crushing the shadows to avoid overexposing the bright areas. We say that the human eye has a high dynamic range and the camera has a low dynamic range.

    HDR is about trying to recreate the way your eye can perceive all the details even in a scene with large differences in brightness. We have to do this with cameras that can’t naturally capture all of the different levels of brightness in a single shot, so instead we take several shots at different levels of exposure. Some with faster shutter speeds to capture the highlights, and some with slower shutter speeds to capture the shadows. These shots then must be combined into a single HDR image (which preserves the brightness differences from the original scene) using special software. Now, your computer monitor and really anything that you’re likely to be viewing these pictures on will be a low-dynamic-range medium, so the HDR software must do something called “tone mapping” to produce an image that looks natural. The best tone mapping algorithms look just like you’re there. The worst ones look like crap.

    #11844

    QuickSilver
    Participant

    I have read about astrophotographers stacking images to achieve a superior image and there are several pieces of software out there labeled for that specific task. The one that comes to mind was produced by Meade and called Autostar Suite. Is this the same thing as HDR? ❓

    #11845

    Analogy
    Participant

    Nah, what astronomers do is more like lowering your ISO and taking a longer exposure.

    #11846

    dangerdizzy
    Participant

    I have read about astrophotographers stacking images to achieve a superior image and there are several pieces of software out there labeled for that specific task. The one that comes to mind was produced by Meade and called Autostar Suite. Is this the same thing as HDR? ❓

    Nah, what astronomers do is more like lowering your ISO and taking a longer exposure.

    Actually, you’re both correct. Something along the lines of HDR is performed by astronomers, having many exposures at varying exposure lengths then combining the images together in PP. They do this to prevent having blown highlights – much like ordinary HDR.

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