DVL-Digest 622 - Postings: Index - (2) why Roated jpegs Save Smaller - (2) dvsupport.com is up - "Perry" This IS a joke isn't it!? Trailing a review of NAB2000 that hasn't been written yet when the show finished over 5 months ago! Maybe it's a typo and should read NAB2001 Perry Mitchell Video Facilities http://www.perrybits.co.uk/ why Roated jpegs Save Smaller - "Perry" Don't confuse still graphics with video. Most video compression first restricts the color space to cut down on information before compression (e.g. 4:1:1 or 4:2:0 for DV) but AFAIK this is not done for still graphics when JPEG compressed. JPEG uses a form of DCT (Direct Cosine Transform) which then presents the image in a way that enables the lossy compression process to work. This is mostly a process of discarding information that is deemed to be of little relevance to the viewer. For a given image, once this information is discarded the first time, subsequent compression cycles should show little change (ignoring the secondary artefacts which produce the 'mosquito trails'). However, if the image is moved (such as a rotation) then a completely different set of information will be presented and a further amount discarded. The original discarded information will not of course be regained, so overall there will be a distinct loss of quality and of course a reduction of the data size as noted. Perry Mitchell Video Facilities http://www.perrybits.co.uk/ why Roated jpegs Save Smaller - "Perry" I will have a play with Photoshop over the weekend and report back. Perry Mitchell Video Facilities http://www.perrybits.co.uk/ (diese posts stammen von der DV-L Mailingliste - THX to Adam Wilt and Perry Mitchell :-) [up] |
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