44.1 Overview

This library provides functions to deal with palettes. As the name implies, a palette is a palette (= set) of colors. The minimum number of colors in a palette is 2 and the maximum number of colors in a palette is 256. The individual colors in a palette are referred to as pens. Those pens are addressed through their indices within the palette, starting from 0. Thus, the first pen in a palette is pen 0, the second one is pen 1, and so on. There can be one pen in a palette that is marked as a transparent pen. Pixels that use this pen, e.g. in a palette brush, will appear transparent then. Typically, pen 0 is the transparent pen.

The number of colors in a palette is referred to as its depth and it is always expressed as a power of 2 exponent. The following depths are available:

‘1-bit:’

2 colors.

‘2-bit:’

4 colors.

‘3-bit:’

8 colors.

‘4-bit:’

16 colors.

‘5-bit:’

32 colors.

‘6-bit:’

64 colors.

‘7-bit:’

128 colors.

‘8-bit:’

256 colors.

Because of the limited number of colors that can be stored in a palette, palette graphics are no longer widely used today. However, using palette graphics does have some advantages over using RGB graphics in certain situations, for example:

• – Palette graphics make it very easy to implement certain effects like color cycling or fading. Because of the limited number of colors that need to be modified these effects can be computed in very few CPU cycles.

• – Memory consumption is much lower than when using RGB graphics. For 32-bit RGB graphics, a single pixel will require 4 bytes of memory whereas in palette mode, a single pixel will just require 1 byte of memory. Thus, a 1920x1080 image will require about 8 megabytes of memory in 32-bit mode but only 2 megabytes of memory in palette mode.

• – Because palette graphics require less memory than RGB graphics, they can also be compressed better when saving them to disk, e.g. as PNG images. Saving images that don't use more than 256 colors as RGB pixels in PNG will yield a significantly bigger image file than saving it as a PNG that uses a palette. That is why you might want to save images that don't use many colors as palette images if you care about file sizes. Functions like SaveBrush() support palette images as well.

Of course, in order to become useful, a palette always needs to be attached to another object that provides the actual pixel data that should be drawn using the colors taken from the palette. In Hollywood, the following object types support palettes:

• – animations
• – BGPics
• – brushes
• – displays
• – sprites

For most object types, you can just set the LoadPalette tag to True in functions like LoadBrush() to make Hollywood create a palette brush for you. You can also convert RGB brushes to palette brushes using functions like QuantizeBrush() or RemapBrush(). Once you have a palette object, you can change its palette using the SetPalette() function.

Special care needs to be taken when putting a display in palette mode. This will have several implications that you need to be aware of in order to make the most out of a palette mode display. See Palette mode displays for details.