LogLin
Function
This node is typically used when handling logarithmic film plates, typically cineon files either coming from a film scanner, or when writing them out for film recording. It will convert them from the logarithmic color space to the linear color space for accurate compositing, and can then be used at the end of your tree to convert the image back into logarithmic space for film scanning. You would also use this around nodes that only work in 8 or 16-bits, functions like Primatte, Keylight or other plug-ins from third parties. Ultimatte is the exception, as it maintains float values. For a full description of this process, jump to About Logarithmic Color Space .
LogLin's color parameters are linked together by default, so the gBlack and bBlack will reflect whatever the rBlack has. You can of course adjust these to further color correct your scanned plates.
An important point about this node is that it only does color correction - it does not change your bit depth or your file type. When Shake imports the Cineon files, a typically 10-bit file, it will automatically promote it to 16-bits. This process has nothing to do with the color correction.
The default values are supplied by Kodak - if you apply a LogLin in Shake, you should get the same visual result as if you plugged in the same numbers into any other package's logarithmic converter. The range of for the offset and black and white points are 0 to 1023, the range of a 10-bit file (8-bit is 0 to 255, 9-bit is 0 to 511). Every 90 points adjustment of these values is equivalent to a full f-stop of exposure.
Parameters
|
Type
|
Defaults
|
Function
|
conversion |
int
|
0 | This describes is you are converting from log to linear space or linear to log space. 0 means log to lin, 1 means lin to log. |
offset |
float
|
0,0,0
|
These values offset the individual color channels. |
black, white |
float
|
90, 685 | These set the black and white cutoff points. The default values are 95 and 685. |
nGamma |
float
|
.6 | The film negative gamma. The default is .6, as
per the standard Kodak specification. Generally, this number is not touched.
The .6 is an average of the response curves, and may differ from stock to
stock and even channel to channel. Have fun looking it all up on Kodak's
site - check out products/Film/Motion Picture Film, and then check the characteristic
curves. Fun for everybody. |
dGamma |
float
|
1.7 | The display gamma, according to Kodak, to compensate for the monitor's lookup table. This was set to neutralize the Cineon system's standard monitor setting. It's inclusion here is more of a heritage thing. It is highly recommended that you leave it at 1.7. |
softClip |
float
|
0 | The rolloff values on the white point. Default is 0, which gives a Linear break. By increasing this value, you smooth the curve out. |
image LogLin( image In, int conversion, float rOffset, float gOffset, float bOffset, float rBlack, float gBlack, float bBlack, float rWhite, float gWhite, float bWhite, float rNGamma, float gNGamma, float bNGamma, float rDGamma, float gDGamma, float bDGamma, float rSoftClip, float gSoftClip, float bSoftClip );
Script
image = LogLin( image, conversion rOffset, gOffset, bOffset, rBlack, gBlack, bBlack, rWhite, gWhite, bWhite, rNGamma, gNGamma, bNGamma, rDGamma, gDGamma, bDGamma, rSoftClip, gSoftClip, bSoftClip );
Command Line
shake -loglin conversion
See Also
About Logarithmic Color
Space