a. Please what is the difference between RGB Mapping and luminance mapping.
b. Please can you explain the functions of MB 1D Frame Mod and MB Attribute Index parameters.
i'm using Graffiti preset
Are you talking about one of the graffiti grid scan presets from V4? They don't use the Source Alpha brush type.
Please I am using source brush under the brush type control panel.
If you want to use the image brush's alpha channel for the brush shape (and associated anti-aliasing), you need to use the Source Alpha brush type. Otherwise, 255 white in the brush rgb channels masks the brush out, and 254 to 0 blends if your Fill Option is set to Blend. If it's set to From, then there is no anti-aliasing.