Modifying Negative Film Gamma or Reference Levels with the Photo Lab Tool

The transformation between log and linear color spaces is controlled by three parameters: negative film gamma, Cineon reference, and linear reference. Gamma controls the contrast, while Cineon reference and linear reference establish a correspondence between points in the two color spaces. The Cineon code, specified as the Cineon reference, is transformed to the value specified as the linear reference. For example, you may want to base the transformation on the 90% white card and specify a Cineon reference code of 685 and a corresponding linear reference value of 90.

NoteAll Delog and Log parameters are animatable —see Setting Keys Manually and Validating and Applying the Expression String.

The white reference is mapped to 0.9 in linear space. Cineon codes above reference white are mapped to values above 0.9, however, these values can be greater than 1. This tool does not clamp to 1, so there is no loss of information.
All incoming pixels with values between 1 and 95 produce black pixels.

Note All channels are linked by default.

To uniformly modify values with the Log or Delog tool:

Do one of the following:
- Drag the red (R), green (G), or blue (B) channel fields to the right to increase, or to the left to decrease, values uniformly on all three channels. Alternatively, you can also drag the luminance (L) field to achieve the same result.
- Select a single channel that you want to modify by deselecting the Lock button.
  Drag the red channel field to the right to increase, or to the left to decrease, the level of the red channel.
  
  The green and blue channels are not affected. However, the overall luminance field updates to reflect the change.

NoteYou may also type values into the channel fields and press Enter. In the case of modifying all channels uniformly, when values are typed into any field, the other fields update. The luminance field will update regardless of which method is used to modify the values.

Using the Trackball to Modify Negative Film Gamma, Cineon Reference and Linear Reference

The trackball allows you to modify levels with a more freestyle, intuitive approach. The trackball emulates a typical 360-degree color wheel that can be dynamically changed by dragging the center of the color wheel. Consequently, the effect on the red, blue, and green channels is predictable.

For example, dragging the trackball towards the red portion of the color wheel increases the value of the red channel, but decreases the values of both the blue and green channels, and adds blue and green to the shadows and midtones of the image.

Modifications made using the trackball are cumulative; each movement of the trackball is added to the previous one. The trackball changes color to reflect the degree of change.

To modify levels with the trackball:

Drag the trackball to modify levels in the image.
Note To reset the trackball, channel, and luminance levels, select the Reset button below the trackball or the Reset button in Tool Options area on the right side of the UI (this button resets the entire tool).

Except where otherwise noted, this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License