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    Micro 4/3 - increasing exposure in post
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    I did some experiments with my LX100. According to reviews on dpreview and other places - with photographs, I can underexpose and then raise the exposure on the computer and it is pretty close to indistinguishable from having just exposed correctly to begin with. But of course, with more highlight headroom. I wanted to see if I can do this in video. I shot at 4k. All used the standard picture style with sharpness and noise reduction at -2, except for the second one as noted.

    Attached are three screen captures from Resolve. In the first one, I shot at ISO 200, and then raised exposure about a stop. In the second one, I shot at ISO 200, noise reduction in the camera at +2, and then raised exposure about a stop. In the third one, I shot at ISO 400, and didn't touch the video on the computer. In the fourth one, I shot at ISO 800, and then lowered the exposure by about a stop.

    I'm a total newbie to Resolve, I used the following settings to raise exposure: Gamma +.16, Gain +1.27, Offset 20.8. For the reduction in exposure I set to gamma -.03, gain .9, offset 25.6. I'm sure I can learn more and do a better job (for example the saturation is quite a bit higher in the untouched photo). But I'm not sure if any amount of playing with exposure settings would prevent the noise that I see from showing up. Note that Resolve already downsized to 1080p, as I normally would.

    Clearly, the first one has a lot of noise in the shadows that the third one doesn't. Unfortunately, raising noise reduction in the camera (the second shot), didn't help - it actually made it worse. The last shot - which was initially overexposed, does show a little less noise. So, at least from this limited test - getting exposure right the first time is much more important in video than photos. Which is kinda what I expected.

    200-raise.jpg200wNR-raise_1.2.2.jpg400-keep.jpg
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    #2
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    For me, I try to slightly overexpose (without clipping) and correct it in post.

    If you are not using log video, there is LESS data captured in the shadows.

    Think about it: for a linear 8 bit system, the first 4 bits only capture 16 different levels of darkness.
    The other 4 bits capture 240 (16-255) levels.

    Generally, you don't loose quality when you make something darker, BUT you can when you make it brighter if you get clipping.
    The old photographer saying "Expose to the right" is also true for video.
    Last edited by Digital Frank; 04-04-2017 at 08:20 PM.


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    Thanks for the response. That makes sense, but then why do some sites like DP review indicate in tests that there is no sacrifice in photography to underexpose and then raise the exposure in processing (for certain cameras, and of course when shooting raw). I guess the two differences between a raw photograph and video are the lack of compression, and that the photograph is 12 or 14 bit. So 12 or 14 bits are basically enough to store shadows without noise?

    Here is an example site I found from google: http://improvephotography.com/34818/iso-invariance/


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    Quote Originally Posted by Digital Frank View Post
    For me, I try to slightly overexpose (without clipping) and correct it in post.

    If you are not using log video, there is LESS data captured in the shadows.

    Think about it: for a linear 8 bit system, the first 4 bits only capture 16 different levels of darkness.
    The other 4 bits capture 240 (16-255) levels.

    Generally, you don't loose quality when you make something darker, BUT you can when you make it brighter if you get clipping.
    The old photographer saying "Expose to the right" is also true for video.

    This is not true of recording 8-bit video, which is gamma corrected for equal number of grayscale steps for every stop. The first stage AD in the camera does digitize linear data, but that is usually 16 bit or at least 14 bit these days. 8-bit video is gamma encoded for 256 equal value steps taken from 16 bit linear data. Compression and chroma subsampling is what reduces value rendition in deep shadow due to macro blocking close values. Noise reduction tends to muddy things a bit too.
    Moderate underexposure, one or two stops, is an effective technique for protecting highlights in wide DR high contrast conditions if used correctly. I routinely recorded video with my old Canon GL2 at 1-1/2 stops under in high contrast outdoor daylight conditions with excellent results. 8-bit video is a 9.5 stop DR medium. Within a narrow range, choosing to protect or sacrifice either highlight or shadow rendition is a creative choice.


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    Senior Member Cary Knoop's Avatar
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    Quote Originally Posted by Digital Frank View Post
    Think about it: for a linear 8 bit system, the first 4 bits only capture 16 different levels of darkness.
    The other 4 bits capture 240 (16-255) levels.
    That is true but no camera works like that.
    The acquisition from the sensor is higher than 8 bit and then the information is gamma curved during encoding to 8 bits.

    Edited to add: just noticed the prior reply which explains the matter very well.


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    So if the video was recorded raw, would there be no sacrifice to increasing exposure in post processing? I think I can try that out in my 70D using Magic Lantern. Note that the 70D isn't an "iso less" sensor unlike others, but I can see what I get.

    But when recording compressed video in the camera, there is a sacrifice to increasing exposure in post processing - you will get lower image quality in the shadows from noise reduction / compression - but obviously it may be a better choice than blowing out highlights.

    Is that about right?


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