- general
- image strip
- compression
- decompression
- combining sprites
Combining Sprites in an Image Strip
The interactive Adobe Flash pixel art illustration is divided into 72
regular shaped rectangles. Per rectangle a compressed image strip is
calculated, based on the compression technique previously described.
This results in 72 image strips containing a certain amount - depending
on a predefined minimum amount of different pixels - of rectangles with
different dimensions.
The next, fairly difficult, problem is how to combine the separate
images of an image strip in order to get an image strip with the lowest
possible surface, which means an image strip with a minimum amount of
redundant space.
If an image strip has e.g. 32 rectangles with different sizes, the
possible options are astronomical. Even with a very fast computer, it's
impossible to calculate them all.
To calculate a good option - not necessarily the best one if the numbers
of rectangles are relative high - I start with the first rectangle, and
position this rectangle on position 0,0. The next rectangle is
positioned on the right side of this rectangle, or at the bottom left.
This process is repeated until all rectangles are positioned.
The first time the last rectangle is positioned the overall surface is
calculated and used as the minimum surface. The next step is to
reposition the last rectangle to a new available position. This is one
of the positions on the right side or bottom left side of previous
rectangles. The new overall surface is calculated and compared with the
minimum surface.
If all possible positions are calculated, the rectangle, before the last
rectangle, is repositioned and the whole process is repeated again...
etc., etc.
By adding some extra checks to bypass solutions that are not relevant, the calculation of a reasonably good solution is do-able.
The next example illustrates the process. The example image strip
contains four different-sized rectangles.
A few possible options are drawn; option 18, 19 and 20 are the most
efficient solutions, which means they have a minimum amount of redundant
space.
Adobe flash can't cope internally with images bigger than 2800 pixels to reconstruct the original images. To bypass this restriction, I use several image strips to rebuild all 72 image strips.
The next image show two image strips used for the detail animations.
The black areas are redundant space.
