AHD and VNG interpolation artifacts

[tomczak]

AHD and VNG RAW interpolations can produce artificts, especially visible in shadows and when original RAW file is noisy. AHD produces a 'maze' or 'rods' like artifacts, while VNG is more like salt and pepper, lonely single pixel high-amplitude noise.

Since they have pretty unique character, I started thinking of a way of removing them, without obliterating details, before sharpening, but I can't figure out a good technique. Median, Blurs or USM with thresholds don't quite cut it, because these artifacts have higher amplitude than details, which will be removed first. AS speck removal is probably the closest to what I want, but it's still hard to separate these artifacts from details. Are there other techniques?

[den]

You might try experimenting with DCoffin's 'dcraw' options:

INTERPOLATION OPTIONS
-f
Interpolate RGB as four colors. Use this if the output shows false 2x2 meshes with VNG or mazes with AHD.
-m number_of_passes
After interpolation, clean up color artifacts by repeatedly applying a 3x3 median filter to the R-G and B-G channels.

If you need a Windows 'command line' "dcraw v9.10" executable, I can make it available. It is only 324KB... but if you have SNS-HDR Lite/Home/Pro v1.4.2 installed... it is located in the their 'Program Files' folder.

[tomczak]

Could such options be made available in PWP RAW? (but it may not be as easy as adding a switch, I imagine...).

[ksinkel]

If you note the progress bar, raw already includes an artifact reduction step.

Kiril

[tomczak]

True. Perhaps it is the number of passes of the median that would have to be increased to remove the artifacts in this example... I'll experiment with dcraw and report. Did others try it before?

[den]

Maciej...

I came across a 'dcraw' GUI that appears to have a 'blink' comparison feature that may be of interest... good for Windows Vista-32/W7-32 and uses v8.94/8.95 (June 2009) versions of dcraw ... default language is Spanish with English selectable... may have to use a Google or Bing translator for portions of the web pages... good list of links regarding dcraw use.

I have downloaded/installed it but haven't explored yet... more familar with using 'command line' options.

MEGUIv4.4 (June 2011) description: http://meguidcraw.blogspot.com/
and click on "Descarga / Download" to get to the download page [Download is a 1.4MB zip file].

[den]

MEGUIv4.4 Update...

I have not been successful to get this program to fully execute without a 'Program has stopped working' dialog [Vista 32 Home Premium, latest updates]. In truth, it really has nothing to add to guide one in the selection of options. It uses verbatim text from DCoffin's Manpage at: http://www.cybercom.net/~dcoffin/dcraw/dcraw.1.html.

I have uninstalled MEGUIv4.4, having elected to continue using 'command line' options added to a desk top Shortcut Properties/Target created from SNS-HDR v1.4.2's "dcraw.exe" [v9.10]; and the select and drag/drop file(s) features of the Vista OS... with 'pixel peeking'/comparisons/analysis using PWP transforms/tools...

FYI, my typical options for a Canon 350D CR2 file are: -v -n 20 -H 0 -w -o 1 -q 3 -m 1 -W -b 1 -g 2.4 12.92 -6 -T

This creates a CR2 full sized, sRGB, AHD, raw conversion 16-bit tiff that will further require (1) PWP RGB Brightness Curve transform editing to establish White Point, Full Range, and preference midtone/shadow brightness; and (2) sharpening and local contrast enhancement.

My apoligies if anyone else has had difficulty in trying out MEGUIv4.4.... There really is not that much to be gained in its use.

[tomczak]

What's known about PPG interpolation?

[MarkT]

I have found that "Bilinear" interpolation used via ufraw/Gimp produces the cleanest outputs. Not sure if this is am option of dcraw or of ufraw though...