SprToJPEG - Sprite to JPEG convertor

by George S. Kapogiannopoulos


SprToJPEG generates JPEG (Joint Photographic Experts' Group) image files from Sprite files and it works both in RISCOS 2 and RISCOS 3. The compressed files can be used with various viewers, such as ChangeFSI. The Program supports Sprites having 256 colours or more. The JPEG format is
a very convenient way of storing images and provides very good compression so
that images that are converted to JPEG format use very little disc space. The
example 24 bit sprite provided takes up 107K of disc space. After converting
it to JPEG, it uses just 7K at a quality setting of 75%. Acorn makes use
of the JPEG file format to compress the example images provided with the
Risc PC.

The program can be loaded by double-clicking on its icon in a directory
display or by clicking on the icon in the RISC User menu program. When it
has loaded, an icon will appear on the icon bar and a directory display will
open. To convert a sprite, simply drag the sprite file to the SprToJPEG icon
bar icon. A save box will appear allowing you to save the file wherever you
want.

A 16 million colour example sprite is included with the application
directory so that you can try out the program. The sprite is in the file
250GT in the directory display which is opened when you run the program.
Once you have created some JPEG files, you can view them by loading
ChangeFSI, which is on the RISC OS support disc or, if you have
a Risc PC, in the Utilities directory of your hard disc. Load
ChangeFSI by double-clicking on it, then you can display JPEG files by
dragging them to the ChangeFSI icon on the icon bar. 


Menu Options
The Quality option sets the quality of the compressed JPEG file. Settings should be between 50 and 95. The default quality 75 is good enough for almost any image. Higher settings on quality increase dramatically the JPEG file size for hardly any gain in output image quality. Settings around 5 to 15 give a warning message because some JPEG decoders may be unable to read the resulting file. The Greyscale option forces the compressed image to be a gray scale one. The program works best with natural images, giving a compression ratio of 10% to 20%. Computer generated images like line art drawings or cartoon graphics which have large areas of the same colour are not compressed very efficiently. The latter can be compressed better by using GIF (Graphics Interchange Format) or by using an archiving program.

Feel free to contact me for bugs, comments or whatever:

Mail:	George Kapogiannopoulos Megdoba 18,
	131 22 Nea Liosia,
	Athens,
	Hellas (Greece).

Email:	georgek@iit.nrcps.ariadne-t.gr
	gkapog@di.uoa.ariadne-t.gr


 Copyright RISC User 1994