Light Graffiti

Description

This effect/filter creates light graffitis from a video by keeping the brightest spots.

Parameters

Statistics (above the keyframe ruler)

The stats switches allow easy and accurate adjustment of the threshold parameters.

Parameter	Value	Description
Show brightness statistics	Switch	If on, displays the brightness and threshold, for adjusting the brightness threshold parameter. Example: To adjust the brightness threshold, check this box and adjust the threshold until the whole light source is highlighted. Repeat the same with the other parameters. Only parts that are highlighted in all thresholds will count as light source.
Show background difference statistics	Switch	If on, displays the background difference and threshold
Show background difference sum statistics	Switch	If on, displays the sum of the background difference and threshold

Switches (above the keyframe ruler)

Parameter	Value	Description
Transparent background	Switch	Makes the background transparent, allowing to apply a composite effect and paint the light mask over a completely different video.
Nonlinear dimming	Switch	If on, uses nonlinear dimming (may look more natural)
Reset	Switch	Use this to reset the clip if you need to adjust parameters. The effect will not reset if the clip is played again, so you need to do this manually.

Nota

If Reset is not switched off, the effect will not produce any visible results.

Parameters

Parameter	Value	Description
Brightness threshold	Integer	How bright (`R+G+B`) does a pixel need to be in order to be recognized as a light source? Increasing this threshold requires brighter light sources (i.e. more white or less color, respectively) but prevents some «false alarms» where semi-bright parts, e.g. hands where colors can change quite a lot compared to the background, are incorrectly recognized as light source.
Difference threshold	Integer	How much does the strongest color channel of a pixel have to change, compared to the background image (`max(dR, dG, dB)`), in order to be recognized as light source? Increasing this threshold makes it harder for light sources to be accepted on bright backgrounds, but decreases the danger of noise or generally bright spots counting as light source.
Difference sum threshold	Integer	How much does the sum of all color channels relative to the background image (`dR + dG + dB`) have to change until a pixel is recognized as a light source? Raising this value might, in some cases, avoid that some light objects lit by the light source are added to the light mask.
Sensitivity	Integer	For slowly moving light source try to use a lower sensitivity to obtain a better exposure.
Lower overexposure	Integer	The light mask does not get white immediately when the light source is moving slowly or staying steady.
Dimming	Integer	Dims the light mask. Lights will leave a fainting trail if it is set to a value > 0.
Background weight	Integer	Strength of the (calculated) background image. Setting it to 100 paints the light mask directly over the background, without the painting person in the image if the video starts with a «clean» background image. (See the α parameter.)
α	Integer	Determines how the effect tries to adapt to background changes. The Light Graffiti effect remembers the first frame of the clip it is applied to, so the clip should always start with the painter outside of the video. If the background constantly changes, e.g. on a street, try to set α > 0 to calculate an average background image.
Saturation	Integer	Increases the saturation of lights.