stewartpratt wrote:... Hm, from reading that I think you may be misunderstanding what decompression is ...
Probably. Many thanks for the explanation. Since I normally talk only to myself about such matters my terminology tends not to be too exact. But as I understand it, when a JPEG is 'Saved For Web' to reduce its file size, the lost data cannot be recovered because the 'compression' is lossy. The original file from which the optimised version was saved needs to be kept separately.
But with, for example, ZIP files, all the data is recoverable. I don't use TIFF files but I understand they are more flexible and also allow 'lost' data to be recovered.
Tom Richardson wrote:(... don't have a go at me or else I will print your message out and hang it on the nail in the outside midden)
Sorry. I wasn't having a go at you (honest).