Archived posting to the Leica Users Group, 2007/01/11
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]A quick look at compression..... and lossy vs, non-lossy..... this is really a quickie and basic explanation. Usually the compression algortihims are quite complex. Here I have used an easy algorithim. Actual compression algorithms are a lot more complex, but this example shows the principles. Note.... compression has nothing to do with photographic images, It is a mathematical process used on a st of data. One of the chief uses for compression is image compression. Original data.....a series of binary bits 0111110010001011111111111 Compression without loss.. hex format 0500100010C Compression with loss I guess I could do this more elegantly, but think of it as a math relationship on every 5 bits, averaged and outputted as a single bit.... 10011 When uncompressed, the results are possibly Lossless: a precise replication of the original data 0111110010001011111111111 Lossy: a mathematically derived representation of the original data. 11111000000000011111111111 Why the difference? Loss. The whole issue of loss is compression density vs fidelity. Mathematical representations are approximations of the original data. ( some simple examples include truncation by rounding, multiplication and keeping the same number of input and output bits, etc.) This gets REALLY nerdy, and I am afraid Ted would throw a fit or reach for another bottle of his favorite whisky. So suffice it to say that Lossy compression is representational and lossless is accurate. ALL the printers that you use at home, and let's say 99.9999999% of the prints you have made at most labs are lossy prints. Where do you think the extra pixels come from? Decompressed data from the image file. So iin the long run, 99.999999999% of all your images now are involved with lossy algorithms, no matter how you took the original capture. Frank Filippone red735i@earthlink.net