Any suggestions on how to "onion skinning"?

[Luis]

 From Wikipedia: http://en.wikipedia.org/wiki/Greyscale

'Converting color to grayscale

To convert any color to its most approximate level of gray, first one  
must obtain the values of its red, green and blue (RGB) primaries.

Then, add 30% of the red value, 59% of the green value, and 11% of  
the blue value, together. Regardless of the scale employed (0.0 to  
1.0, 0 to 255, 0% to 100%, etc.), the resultant number is the desired  
gray value, such that a new RGB color would have red, green, and blue  
values equal to the new number. These percentages are chosen due to  
the different relative sensitivity of the normal human eye to each of  
the primary colors (less sensitive to green, more to blue).'

Cheers,

Luis.


On 29 Nov 2007, at 09:54, Luis wrote:

> Hiya,
>
> Some time ago we used to add the RGB values together and then  
> divide by 3. This was waaaay back, and the results were ok then.
>
> I spotted this on the net:
>
> R*.3+G*.59+B*.11 to get the grey value, haven't tried it.
>
> Cheers,
>
> Luis.
>
>
> On 29 Nov 2007, at 00:39, Ken Ray wrote:
>
>> On Wed, 28 Nov 2007 20:50:11 -0200, Andre Garzia wrote:
>>
>>> Ken,
>>>
>>> Have you tried snapshoting the card, then somewhere off screen  
>>> you put
>>> a gray image on top of the snapshot with some blend and take another
>>> shot. Depending on ink combinations you might have a nice result.
>>
>> Good idea - I'll compare that speed-wise with other suggestions  
>> people
>> have made.
>>
>>> Another way, which I don't know how fast it is, is to read each  
>>> pixel
>>> in the snapshot and convert it using some proportional gray value.
>>
>> Yeah, that was Chipp's suggestion - which I might use too - took  
>> about
>> 500ms on a 400x400 image on my MacBookPro.
>>
>>
>> Ken Ray
>> Sons of Thunder Software, Inc.
>> Email: kray at sonsothunder.com
>> Web Site: http://www.sonsothunder.com/
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