The effect is that tones in the upper-most stop of light can be described by nearly 1500 different variations, whereas tones in the lowest measured stop of light can only be described by two possible values - on or off. The "knee" that occurs on the left side of the graph is not caused by an applied curve, but rather, the fact that more and more pixels are clipping to 0 with each diminished stop of light, causing the average to diminish at a decelerating rate (as there are no negative values to work with).Īn important observation here is that even though stops of light are logarithmic (one stop is a doubling of light) the CMOS sensor measure light in a linear fashion and the RAW file records those values in a linear value scale.Within one stop above the point I have labeled for black. Pure white occurs somewhere within one stop below the point for which I have labeled "RGB White". I am using whole stop increments, so don't get too hung up where exactly the RGB clipping is occurring.I have noted where the JPG (OOC) went completely to black (RGB Black) and white (RGB White), and the properly metered exposure (METERED 0 EV).
For each exposure I have noted the shutter speed followed by the average green value from RawDigger, the tick mark lines up with where that average actually falls on the logarithmic scale.Clearly, the 8 second exposure is clipped against the RAW upper limit, values indicate clipping occurs about 1/3 of a stop above the 4' exposure.
In this particular exposure sequence using shaded sunlight the Red and Blue channel lagged about a stop behind in the values shown here for the green channel. In the RAW format, black starts at the value of 255.
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