LF: Grabber image format

[MarkusVester@aol.com]

Dear LF Group,

today I have changed the 8-bit image format for my grabber from .gif to .png. This appears to save some 20% of volume, due to a more effective lossless compression algorithm.

When I started grabber operation I had tried various flavours of .jpg first, but the halved colour resolution soon turned out inadequate for many fine details on the colour-DF display. With 256 colours and lossless compression, resolution looked much better, but very weak signals and noise details tended to get masked off by too few dark palette entries. I got around that by brightening the original bitmap (gamma=1.49 in IrfanView) before reducing to 8 bits, and then darkening the colour table again (gamma=0.67) before uploading.

Please report if you find any difficulties displaying or downloading the .png images.

73 de Markus, DF6NM

http://members.aol.com/df6nm/Grabber.htm