Any suggestions on how to "onion skinning"?

Wilhelm Sanke sanke at
Thu Nov 29 04:48:57 EST 2007

Mark Smith mark at wrote:

> This is sort of interesting:
> if you simply take one of the color bytes of each pixel, and copy it  
> to the other two color bytes, you get a gray-scale result. The  
> brightness/contrast varies with which color you choose. For the few  
> images I've tried, it seems to be red =brighter/less contrast  to  
> blue= darker/more contrast. This may be no surprise to the pro image  
> wranglers among us, but seemed intriguing to me.

And Chipp Walters chipp at wrote:

> Mark,
> Unless you average the 3, your gray-scale result may not work
> properly. Try it on an image with 3 circles: 100%R, 100%G, 100%B and
> you'll see what I mean.

My experience is that with most photos you get a very nice grayscale 
image using the red pixel and copying the value to the other two pixels 
like Mark suggested.

The last public version of my "Imagedata Toolkit Preview 3" (update of 
April 17)


contains both grayscale routines using "average" and those with copying 
one color pixel to the other two - implemented for all three colors.

Speed for "average gray" and a 640X480 image (on a 2 GHz machine) is 
about 1.1 seconds and for "gray from red" about 600 milliseconds.-

The next update of the Imagedata Toolkit, which will be the last with a 
restriction to an enforced image size of  640X480, will probably be 
released before Xmas and contain a number of major enhancements (among 
them: scripted Rev emulation of cubic enlargement, integration and 
expanding of some new Gluas filters from Gimp - translated into 
Revolution - "stretch contrast", "compress contrast", enhancement of 
"jitter" filters with various multi-pixel jitters, another despeckle 
filter based on minimum differences between surrounding pixel pairs 
[this is another Gimp/Gluas development that is identical in 
effectiveness to the "median" approach, but somewhat slower], exchanging 
color values within a defined range by clicking on image and/or color 
scale, copying - and enlarging or shrinking - and pasting oval or 
rectangular portions of an image into the same or another image with 
variable fringe and/or overall blending into the basic image).

Best regards,

Wilhelm Sanke

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