On 27 Sep., 23:07, Erik Krause <[email protected]> wrote: > Am 27.09.2011 15:16, schrieb Calvin McDonald: > > > Can someone tell me why in general someone would want their pano > > downscaled by Hugin? > > In other words, is there a good reason to set this to something besides > > 100%? > > Yes. The 70% rule was introduced by Ken Turkowski, QTVR pioneer at > Apple. He found out that you can downscale a Bayer interpolated image > (as most digital camera images are) to 70% without loosing relevant > image information. You can try it: Downscale an image to 70%, then > upscale again to original size. Compare with the original.
I tried, and indeed the difference is nearly invisible. When I put the original and the scaled-down-and-up-again image in two layers and looked at them with difference layer mode and brightened by a few 100 percent, a ghost image occured showing what had gone missing: very fine contrast. Not really visible at all, even though it's detectable - and I only used cubic interpolation, so if I used something better the effect migt even be less. This was on a landscape taken RAW with a decent lens on a EOS 450D, > This might or might not hold true, depending on image content. While > color information is indeed upscaled during Bayer interpolation, > brightness information could be taken from any sensor pixel. Hence one > could assume that a more or less black and white image with high > contrast might suffer more from downscaling than a low contrast but very > colored one. The differences were largest in areas with small detail, as expected (grass in the foreground) and along high-contrast edges. I'd add that it does also depend on what camera/lens you're using. If I take zoom images with the 450 D's kit lens, I don't even expect 70%. And when the images are warped and blended, there's two more processing steps which lower resolution, so the resulting image is slightly blurred compared to the input anyway (unless there's some superresolution magic going on). 70% is probably even a bit optimistic, then. I usually go for something like 50 - the visible difference is small and proecessing is much faster. Kay -- You received this message because you are subscribed to the Google Groups "Hugin and other free panoramic software" group. A list of frequently asked questions is available at: http://wiki.panotools.org/Hugin_FAQ To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/hugin-ptx
