DVL-Digest 624 - Postings: Index 35mm Blow Ups JPEG empiricals Photoshop 5.0 Text Titles for 35mm Blow Ups - Adam Wilt The best transfers I have ever seen came from a company in Vancoover, BC > that used only NTSC and a proprietary process they developed. In the past > 2 years I have seen a lot of DV to film transfers and this place was the > best, even over PAL>film. I can't remember the name of the place but > there can't be too many in Vancoover. Digital Film Group, Inc.; http://www.digitalfilmgroup.net/ Cheers, Adam Wilt JPEG empiricals - "Perry" I promised to come back with some experimental conclusions so here'tis: (all experiments conducted with Photoshop) 1) There is no colour prefiltering with still images to change the colour mapping. (unlike video) 2) The luminance and color components get the same spacial resolution. It appears that the color components get a lower value resolution. At higher extremes of compression, the anti aliasing pixels can be compromised resulting in an apparent loss of resolution. 3) Compression blocks are square, not rectangular as had been suggested. So to come back to the rotate question: there is no particular significance in a rotation of the image, it is just another way of shuffling the information in the compression blocks. you could get a similar result by moving the image a non multiple of 8 pixels. In summary: If you save an image with JPEG compression, the algorithm will discard some information as being less important (redundant) to the viewer. If you then re-open this image and resave it with the same JPEG parameters, the information has already been discarded and so the second JPEG file has almost the same data size as the first. If you move the image, the compression blocks change and a new set of redundant information is discarded, resulting in a smaller but lower quality file. The bottom line is that quality does not get lost, and data size does not get smaller, unless the image is moved between generations. Those of us that have conducted generation tests with DV already knew this to be true. Note that these conclusions are relevant to the first order effects. The JPEG algorithm produces artefacts that are often called mosquito trails, and these will tend to accumulate and get worse in subsequent generations. Perry Mitchell Video Facilities http://www.perrybits.co.uk/ Photoshop 5.0 Text Titles for - Adam Wilt I have been finding that text titles I create in Photoshop 5.0 for use in > Premiere 5.1c as scrolling text via the image pan filter produces > "flickering" text edges as the text scrolls up the screen. Have a look at http://www.adamwilt.com/Tidbits.html#CGs and see if that helps solve your problems. Cheers, Adam Wilt (diese posts stammen von der DV-L Mailingliste - THX to Adam Wilt and Perry Mitchell :-) [up] |
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