| cgBlendImage, more than 2 images? [message #90716] |
Thu, 02 April 2015 07:25  |
sam.tushaus
Messages: 14
Registered: February 2015
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Junior Member |
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Hello! I was wondering if anyone had tried using cgBlendImage to blend more than 2 images. I have 4 images - I've tried blending 2 of the images, blending the other 2, and blending those together, but I've had no luck thus far. Has anyone tried this? Should I simply stick with two separate blended images instead?
Thanks!
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| Re: cgBlendImage, more than 2 images? [message #90718 is a reply to message #90717] |
Thu, 02 April 2015 10:11  |
sam.tushaus
Messages: 14
Registered: February 2015
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Junior Member |
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On Thursday, April 2, 2015 at 11:40:39 AM UTC-5, Mike Galloy wrote:
> On 4/2/15 8:25 AM, wrote:
>> Hello! I was wondering if anyone had tried using cgBlendImage to
>> blend more than 2 images. I have 4 images - I've tried blending 2 of
>> the images, blending the other 2, and blending those together, but
>> I've had no luck thus far. Has anyone tried this? Should I simply
>> stick with two separate blended images instead?
>
> I don't know the details of cgBlendImage, but if you want to blend four
> images like:
>
> I = a * I1 + b * I2 + c * I3 + d * I4
>
> where a + b + c + d = 1, then you should blend the first two images
> together to get I12:
>
> I12 = a / (a + b) * I1 + b / (a + b) I2
>
> Blend images 3 and 4 to get I34:
>
> I34 = c / (c + d) * I3 + d / (c + d) I4
>
> Then blend the I12 and I34 to get the result:
>
> I = (a + b) / (a + b + c + d) * I12 + (c + d) / (a + b + c + d) * I34
>
> Is that what you are doing?
>
> -Mike
Yes! That's what I was trying to do. I'm not sure where you're getting a, b, c, and d though - I'm not weighting each image by anything. I don't think it's necessary, from the documentation.
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| Re: cgBlendImage, more than 2 images? [message #90719 is a reply to message #90718] |
Thu, 02 April 2015 17:02 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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sam.tushaus@gmail.com writes:
> Yes! That's what I was trying to do. I'm not sure where you're getting a, b, c, and d though - I'm not weighting each image by anything. I don't think it's necessary, from the documentation.
It's necessary. The values a, b, c, and d are numbers that sum to 1.0. I
would do this the way Mike advices.
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thue. ("Perhaps thou speakest truth.")
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