wwp@yahoogroups.com:
Re: Full Screen VR
Andrew 2004-Jun-30 05:28:00
> So you mean that the scale which is used by Adobe and Quicktime and which
> corresponds very close to the independent JPEG Group is not the standard.
I didn't explored PhotoShop, but can say about QuickTime - yes, QuickTime framework (which is used by CubicConverter and perhaps all other tools on Mac, has non-linear, non-standrd JPEG compression scale.
Make a simple test by own - save your movie with Quality set to "Least" according to 5-speeds slider. QuickTime's JPEG compression is 0 now. But jpegdump estimates it as 25 standard JPEG quality. And you could check it by your own eyes - your panorama is still OK, although is hard compressed. If this would really applied 0 standard JPEG compression this would destroyed the image completely but you still see details because it's 25.
BTW I see nothing strange in fact that QuickTime (and perhaps PhotoShop) uses own compressions scale.
> This is a good article where you can also see how the IJG compression and
> the photoshop are very close to each others.
> http://www.photo.net/learn/jpeg/#ijg
>
> According to the above article JPEG dump measures the IJG compression
> scale.
> I do not know how you measured it with Jpegdump. but it definetly does not
> correspond to
> IJG or Photoshop. compression rates.
I need to note that jpegdump estimates very close to the real compression values.
I have tested it with popular PC programs IrfanView, Picture Window Pro, PhotoShop's "Pro JPEG" plug-in and JPEG quality was estimated 100% right. About PhotoShop - ;-) - it has the same primitive few-stops slider (at least my version) as QuickTime has and I have no luck (no time) with testing it.
=Andrew Jakowleff