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Broken Sword: Palletized JPEG for Game Boy Advance Broken Sword is a graphical adventure game re-implemented from scratch to work on the Game Boy Advance. Selecting the right compression techniques for various data is important for all games and never more so when you want to squash as much as possible onto an 8MB cartridge without resorting to content butchery. The largest chunk of our storage budget was given to animation data, but the game also contains roughly 150 unique background images, nearly 80 music cues complete with orchestral sample set, a suite of SFX samples and five languages worth of dialogue. Uncompressed, the backgrounds in Broken Sword would occupy close to 7MB. This article discusses the technique we used for storing lots of high detail unique backgrounds for use with character (tiled) BG modes. There's no glamor here I'm afraid; this article presents a useful, flexible solution to the meat and potatoes problem of managing a large number of background graphics. Design Deciding
on a graphics mode to best fit the game was first port of call after identifying
all visual requirements. We decided to use a screen mode which supports
256 colors because JPEG compression suits detailed images particularly well, so it was a natural first choice for storing our backgrounds. Not only is it very powerful, crunching images down to impressive ratios, but it's very flexible too. JPEG compression can accept a quality parameter, making it very simple to play the quality of the resulting image against its compressed size. We exploited this in our build process by applying an initial global quality level to all backgrounds, set as low as we could get away with, then spending the remainder of the budget individually improving any backgrounds that decompressed with too many ugly artifacts (those with large areas of solid color in particular). Figures 1 to 3 give an example of JPEGs flexible quality control. It's also worth noting that both the artifacts and the decrease in saturation subtleties that JPEG introduces are much less noticeable on the Game Boy Advance LCD.
For ten representative backgrounds, on average, JPEG compression, set at a quality of 50/100 compresses images down to 30.2 percent of their original size. With a quality setting of 35/100 this becomes 24.8 percent and at 20/100 its down to 18.1 percent.
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Design
Features
