That means highlight clipping would be recorded at around 180, with no image details recorded in the range 181-255. On a camera with an 8-bit codec like the GH4, you would have a scale from 0-256. The vertical calibration on the chart is a 10-bit scale from 0-1024. ![]() That would appear to sacrifice the camera's 80-109 IRE range, for the sake of allowing you to use Varicam V-Log LUT's interchangeably with GH4 V-Log-L footage. In order to match the V-Log curve, he claims you should set exposure for highlight clipping at 79 IRE. That's where the GH4's 12-stop dynamic range ends with highlight clipping, 4 stops short of the 16-stop range of the Varicam's V-Log tone curve. The important issue, however, is that green rectangle Barry drew on the chart at stop 4. This is the part of the dynamic range that must be accurately exposed in order to match the non-log segment of the V-log LUT you select. Note how the flat log segment of the curve extends down to about -4, with a rolloff knee down to 0% reflectance in the bottom 4 stops of the shadow range. The chart shows 16 stops from -8 to +8, with zero calibrated to 18% gray reflectance. Here's a link to Barry Green's explanation of how the GH4's V-Log-L differs from the Varicam's V-Log tone curve: Standard color correction tools are insufficient to convert those camera log spaces to a display-referred color space, though many people still try to use them, making the job very difficult and producing inaccurate colors. For most camera log spaces that transformation involves a matrix or a 3D LUT. A specific transformation is required to convert them to the color space of a display. Scene-referred images aren't meant to be displayed directly. Contrast, saturation, and highlight handling are up to you and your workflow, instead of being determined by the camera and how it was set during shooting. They represent the image in terms of the way the camera's sensor captured it. The images are rendered for a certain type of display, and the look is baked in.Ĭamera log spaces such as S-Log and V-Log are scene referred. Standard cameras record into a display-referred color space: the signals are meant to be sent to a monitor for display, without any manipulation. If you want a purely technical description: īut if you want some context, basically V-Log and V-Log L are the same idea as Canon Log or Sony S-Log, though with specific differences. ![]() And in some circumstances, you'd get banding if the jump is too big.Īnd if this is the case., then why compress the luminances into such a narrow range? Why not scale it to the camera's full luminance range, and preserve as much of the "in -between" luminances as possible? If your camera has a range of, say, 1-1000, then why reduce the image to 300-700?Īs I said, I don't think I'm understanding this correctly. Thus, each luminance value would be doubled: 1 becomes 2, 3 becomes 6, 42 becomes 82, etc.) There'd be no real increase in the range of luminances. Say I have a photo with luminance ranges from 0 to 100, and I scale that to 0-200. It seems to me that if you take a narrow range of luminance, and scale it to a larger range, you don't get pixels with in-between values. I don't mean that it leaves out the highs and lows. But doesn't this mean that the color palette leaves out a lot of value? This enables color graders to "stretch" those values, and thus, have some play with the midrange gamma. V-log delivers a very flat image, where the darkest elements are greyish, and the lightest elements are bright, but not completely blown out. If someone could explain this to me, I'd be grateful. I think I'm misunderstanding something about the virtues of v-log and flat profiles.
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