Digital Light & Color

I played a bit with the AHD and VNG interpolations for the same RAW files and I don't find them that overly different. With low noise images, AHD seems to produce less zipper-like artifacts on sharp edges than VNG, but with high noise images it produces these unnatural mosaic-like structures in smooth areas (VNG makes noise look more natural, but also produces some single-pixel 'spikes' in the noise).

What are other's experiences with it?

The forums at the RawTherapee raw processor software website http://rawtherapee.com/forum/ have dozens of threads comparing many kinds of raw demosaicing algorithms. Maybe a bit of a time-waster to find good discussions among all the Extreme Pixel-Peeping sportsmen, though.

There's always Guillermo Luijk's in depth tutorial for DCRAW at http://www.guillermoluijk.com/tutorial/ ... dex_en.htm which goes into depth on DCRAW's raw image process techniques and options. PWP50 seems to expose some of the options discussed there, so it's useful for background.

For me in general, AHD interpolation seems to provide the best, all around results. The only time I resort to VNG is when I have exceeded a len's diffraction limits during a 'capture'. In this case, I will do two RAW conversions, one with AHD and the other with VNG... ...and use the conversion that will best provide a final preference image when recovering using various sharpening techniques from the softening due to the lens diffraction... ...in some rare cases, I have specific image area Composite-blended the final preference images from the AHD and VNG conversions.

Den, what's the visual/practical difference between AHD and VNG interpolation when developing diffraction-blurred RAW? Why would you bother to use VNG, only for blurred RAW? Is it because of aggressive sharpening and the 'maze-like' AHD noise being emphasized and with sharper initial RAW you wouldn't have to go as hard on the sharpening sliders so the 'maze' doesn't show that much?

OTF: how do you attempt to sharpen such images?

MaciejT....

(1) Never really did consider the differences. AHD and VNG interpolation conversion images just provided differing starting points for specific image area sharpening [and occasionally specific image area noise reduction] and other post-processing techniques. Did not ascertain generic relationships that could significantly be due to the method of interpolation. My overall impression was that the subsequent post-processing techniques obscured the differing interpolation artifacts so that they became essentially a non-factor.

It has been some time since I did this and I was unable to locate my notes... in any event, my current photographic style [Canon EOS-350D] is too limit aperatures to f11 and lower with the camera on aperature priority [usually f8 which seems to be a good 'camera ready initial' setting for compromise DOF and in-focus 'sharpness' considerations] and if I need more speed, to up the ISO from 100... ...so it has been some time since I really had to deal with lens diffraction issues.

(2) lens diffraction recovery sharpening and other difficult recoveries... In addition to the usual suspects: USM, BilateralSharpening, etc. and depending on the desired output resolution: (a) downward Resizing for web image resolutions will often recover from lens diffractions after a 50% to 65% Amount of Sharpen or just printing on 4x6 inch paper letting the printer driver do the sharpening; or (b) for gallery quality prints and 3456x2304 pixel image resolutions, I try:
(i) micro-contrast sharpening with AdvancedSharpen with a setting [*.as file in txt format] and sometimes with the suggested mid-tone mask described in (ii):

AdvancedSharpen 1.0
speckradius 0
speckthresh 255
speckdiffthresh 255
removewhitespecks 0
removeblackspecks 0
blurradius 1.0000
bluramt 0.0000
blurthresh 255 255
blurflags 0
sharpenradius 0.4990
sharpenamt 1.2012
sharpenthresh 4 8
sharpenflags 1
histexpand 2
end

adjusting settings as needed and followed by if necessary, black/white speck removal of 1 pixel of the resulting image version using AdvancedSharpen's Speck Removal tab;

(ii) then HighPass Filter-Hard Light sharpening with a 3 to 5 pixel radius; followed by HighPass Filter-Hard Light sharpening with a 50 to 75 pixel radius [Local Contrast Enhancement]. Both of the HighPass-HardLight sharpenings use masks to limit the effect to mid-tones and to limit the white half of the sharpening to 2/3's of the black half of the sharpening.

The mid-tone mask [Composite-HardLight Input mask] is a Brokenline curve: [0,0], [5,0], [20,40], [50,100], [80,40], [95,0], [100,0] and the mask to control white/black half sharpening ratio [Composite-HardLight Overlay mask] is the default diagonal [0,0], [100,100] with the white amount set to 66.7% and black amount set to 100% when used in the Composite-Hard Light transform.

These two masks when used, will allow the use of the Composite-Hard Light filter rather than the normal Soft Light filter when employing High Pass Filter sharpening sequences without generating objectionable white sharpening halos...