This loader as well as ldr.4Bit&Arith actually are "extensions" to the base loader ldr.4BitGoDot. The included options for screen modification simply had no room in the base loader anymore.

The first of these options (in Compose section Modify Data) is called Bump Map. This is a term located in the arena of raytracing. It allows you to manipulate graphic data into a second picture in such a way that the impression arises you have "coined" something onto the first picture, e.g. a pattern. The process runs according to the following algorithm: all gray values (of the bumpmap to be loaded) below 7 are subtracted from the available values, whereas all values above 7 get added. Bump Map represents something like a combination of Addition (see below) and Subtract (part of ldr.4Bit&Arith). How to easily produce bumpmaps we will describe with the keyword "Convolve". Lader 4Bit&Map Modify

The second option AlphaCh (short for Alpha Channel) enables us to morph two pictures gently into one another. To achieve this, both pictures must be joined with the same alpha picture, one set to pos (-itive), the other set to neg (-ative). You finally add the two intermediate results (you could have saved in the REU for instance; see svr.Temp, Temp, or Undo) to the final picture using the third option Addition (set to: 100%). Alpha channels are pictures, which exclusively mark the transitions of a further picture to a third one. For this it is necessary the alpha channel to be a gray scale picture. Each brighter gray tone lets the picture to be treated (the reloaded one) become a bit more visible, beginning with black (everything covered) up to white (completely transparent).

Note: The resulting pictures are gray scale pictures and are displayed with false colors. Thus they are usable only for printing preparations or to be exported to foreign computers.

From version 1.03 on the loader is able to process clips. For information about handling see ldr.4BitGoDot and svr.4BitClip.

Displayed in "Image Information":

Example pictures:
Bump Mapping Here we used an alpha channel as a bumpmap. Inside (values beyond 7) the picture lightens, outside the "bumpmap" darkens the picture (with values below 7).

The alpha channel consists of a diagonal gradient, which lets our two example pictures flow into one another very beautifully. Alpha Cannelling


Arndt Dettke

Copyright © 1996, A. Dettke, latest update - 12/31/99