Glenn ChanREELSony Vegas Tutorials

Linear Light Processing in Vegas 8

One of the new features in Vegas 8 is the capability to do "linear light processing". Normally image processing is performed on the values as they are, as gamma-corrected values. Gamma correction is used to make storage more efficient. However, it is possible to convert the values to linear light values to get results that are optically correct. This allows for dissolves to be more film-like and for diffusion effects to be more realistic.

Cross Dissolves

Linear light processing.

Normal / Gamma corrected processing.

Diffusion Effects

Linear light processing.

Normal / Gamma corrected processing.

To create this diffusion effect:

1- Superimpose the video onto itself by crtl-dragging it onto a higher track.

2- Add a Gaussian blur videoFX. The images above used the "Extreme Blur" preset.

3- Add Color Curves. Settings can be seen visually below.

4- Set the compositing mode on the upper track to "add".

5- Adjust the opacity on the top layer to adjust the strength of the diffusion effect. As an alternative, you can add a Levels filter and adjust that instead.

Performing linear light processing in Vegas 8

There are a few methods for performing linear light processing in Vegas 8

Method #1: Change the project properties to "32-bit floating point" and change the compositing gamma to "1.000". This will automatically perform all processing in linear light. Be careful as linear light processing is not always appropriate! Certain videoFX will give very different results in this mode (compared to a compositing gamma of 2.222). The "studio RGB to computer RGB" presets will not do what they say. The Color Corrector will yield visible hue shifts when increasing saturation.

Method #1/2: To get around this problem, you can manually 'sandwich' videoFX with gamma conversions so that they yield the right results. Apply a levels videoFX with a gamma of 2.222 before your videoFX. You can change the order of effects by dragging its name left/right in the videoFX window. Then apply a second levels videoFX with a gamma of 0.45 after your videoFX.

In a 1.000 project, the sandwiching technique can be used to get particular FX (e.g. Levels, Color Corrector) to behave as if they were in a 2.222 project. In a 2.222 project, you can apply the sandwich -with the order of the videoFX reversed- to get FX to behave as if they were in a 1.000 project.

Method #3: Manually convert values to linear light values before processing. Create a new track for events to be processed in linear light and move your events onto this track. Apply a Levels videoFX with a gamma of 2.222. If you are also using the pan/crop tool, set the Levels videoFX to be applied before pan/crop by clicking on the Pre/Post Toggle triange in the event FX window (not shown). This will allow image resizing to be performed in linear light.

Finally, apply a second Levels videoFX at the trackFX level (the leftmost red arrow in the diagram points to trackFX).

This will only work for videoFX that can be confined to a single track. This method does not work for the diffusion effect method outlined above.

Method #4: For optically-correct cross dissolves, use the SMLuminance plug-in (third party download). This transition will work in 8-bit projects.

Convert Values to Computer RGB Levels Beforehand

For proper light light processing, convert your sources' levels to computer RGB levels/range (0-255) beforehand. Certain codecs like Vegas' DV codec will decode to studio RGB levels. Convert these clips by applying a Levels videoFX onto it.

In projects with a compositing gamma of 2.222, simply apply the Levels videoFX with the "studio RGB to computer RGB" preset.

In projects with a compositing gamma of 1.000, add a Levels videoFX with an input start of 0.068 and input end of 0.916.



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