The Keying > Luma Keyer effect

The Luma Keyer effect is used to render pixels transparent according to their luminosity.
When you have scanned an image on a white background you obtain a completely opaque layer. With the Luma Keyer effect is is therefore possible to make the white pixels of this image transparent:

Let's take a look at the drawing on real paper above. Application of the Luma Keyer effect set with correct parameters will render the light pixels transparent (independent of their hue and saturation), progressively increase the opacity of the medium tone pixels and leave the dark pixels intact. This gives us the image shown to the right.

At this point, it is possible to re-color the image, if desired : simply place a layer under the image obtained and spread the colors of your choice on it (see example opposite).
You may also use the shape floodfill tools studied in lesson 6.

These are the functions of the Keying > Luma Keyer effect:
* The Display popup menu is used to choose between viewing the source image, the result or matte.
* The color box is used to choose the color the luminosity of which you wish to render transparent directly on the screen.
* The buttons Add and Sub are used to adjust the tolerance and softness of pixel cut-out.
* The mini-sliders allow adjustment of the following, depending on the luminosity and with the help of the diagram below:

The type of pixels which remain opaque
Those which are progressively made transparent
Those which will be completely transparent

It is recommended to combine the Luma Keyer effect in a multiple FX stack with the Colors > Histogram or the Colors > Slider effects to be able to precisely adjust pixel transparency (use the parameters relative to the alpha component) and remove the gray aspect (light) of semi-transparent pixels.

The effects Keying > Luma Keyer and Colors > Scan Cleaner change the opacity of the pixels differently : the Luma Keyer doesn't remove the unwanted pencil marks. The Scan Cleaner change the color of the pixels, and the Luma Keyer doesn't.