The HSVTool node converts the input color space to a HSV color space and converts the adjusted values back to the image input color space for further processing for the output. The HSVTool node is used to adjust the HSV channel components of an image the the Read node stream. It’s basic operation are to adjust the Hue: which is the color of the input image, Saturation: which is the color range of the input image, and Brightness: which is the color value level and the grayscale of the input image.
Each section has a rang controls that can be adjusted to limit the effects of a node by narrowing the input color ranges.
What are some standard work-flow using HSVTool?
You can do secondary color corrections or color replacements with the source/destination eyedropper tool.
You can use the HSVTool for linear/color keying.
You can do an overall color shift by using the rotation range adjuster in the Hue parameters etc.
The following screen captures are based on a single pixel selection without manual component modifications. You will see different alpha mattes display based on the alpha output components.
The image above is the result of a single color pixel selection using the blue destination replacement color.
Brightness adjustment ranges
This is when you make adjustments to Hue, Saturation, and Brightness to limit the input color ranges for the desired effect. You can look at the third viewer on the right that has matte/alpha generated by the color selection key using the source color eyedropper. This is the alpha interpretation of the alpha output component which is the to Hue.
Each of the matte generated displays are based from the colors that are spread across the image on a single pixel selection and it HSV values.
By using a low resolution and/or compressed image you will see the artifacts in the alpha channel. This makes it harder to do a replacement or secondary color correction. Is is evident that the blue channel has the most artifacts/noise, you can use the CImgDenoise or CImgBlur node and blur one or two pixels in the blue channel to soften the pixel edges. This technique will not always work, remember to apply dynamic range applications when using the HSVTool. You can only push the Saturation and Brightness so far. Also remember that HSVTool need color input in order to apply any color filtering even though it can output greyscale and matte data.
When you need to pull a key with the ChromaKeyer the key color is outputted as black or represents a transparency. See node grap below for an example.
The image below is the ChromaKeyer parameters panel. You can see that the eyedropper has a chroma green selection from the input image. You may also notice the acceptance angle is very high, this is because the source material is compressed.
As you can see from the panel the chromakey subtracted the chroma green, replacing it with black/transparent. The “Key Lift” and “Key Gain” clamps the black/white to make a clean matte from the keyed selection.
Even if the chromakey generates transparency from the node, it still outputs a black and white matte that can be used as an inverted mask or holdout matte to apply needed filter effects.
A holdout matte is a section of your image that tells the keyer not to key the selected area. A holdout matte is commonly used to define a area within your image that might have similar colors to the color being keyed.
The node graph below is using the same green screen image when pulling a key with the HSVTool. The alpha output shows up as the white color. This HSVTool does not subtract the color to generate a matte, as oppose to the ChromaKeyer and Keyer nodes that subtracts the color to generate a matte. If you are concerned about color spaces, ChromaKeyer and Keyer process data in RGB color space and the HSVTool process in HSV color space.
The image below is the HSVTool parameters panel. You can see that the source color eyedropper operator has a chroma green selected. As you look further down the panel you will notice the Hue, Saturation, and Brightness parameters which has all the values the make up the chroma green selection.
The important part to remember is that Hue, Saturation, and Brightness are used to generate and adjust the matte(s) based on the output alpha mode. The image output alpha is set to min(All), when selected, Hue, Saturation, and Brightness can be used to adjust the matte/mask output.
There are eight output alpha modes. The only mode that can’t generate a matte is the “Source” mode. Even if there’s no matte generated you can still do color replacements and color corrections.
The image above displays two HSVTool nodes that is keying the same input, but generating two different mattes based on the output alpha. The middle viewer is the Hue mode output. The viewer on the right is the min(Hue, Saturation) mode output. When you are working with compressed source images the output alpha modes will yield different results.
If you need more control on the alpha/matte output, the ColorLookup node can help adjusting edges.