z-projection SUM

[Sarah Locknar]

Hi all-
I have a stack of 24-bit RGB images where the G channel is about twice as
bright as R and B.  When I do a z-projection using SUM, the green intensity
is much lower, while using AVERAGE the relative intensities seem to be
preserved.  Can anyone confirm if the resulting SUM is autoscaled in R, G
and B independently and then recombined for the 24-bit image?  The other
possibility is that some sort of wrapping occurs if the intensity goes
above 255 in a channel (green in my case).
Thoughts?
Thanks
Sarah

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*Sarah Locknar, PhD*
Project Scientist


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[Rasband, Wayne (NIH/NIMH) [E]]

On Dec 6, 2012, at 11:41 AM, Sarah Locknar wrote:

> Hi all-
> I have a stack of 24-bit RGB images where the G channel is about twice as
> bright as R and B.  When I do a z-projection using SUM, the green intensity
> is much lower, while using AVERAGE the relative intensities seem to be
> preserved.  Can anyone confirm if the resulting SUM is autoscaled in R, G
> and B independently and then recombined for the 24-bit image?  The other
> possibility is that some sort of wrapping occurs if the intensity goes
> above 255 in a channel (green in my case).

It does autoscaling. To avoid this, convert the RGB stack to composite color using the Image>Color>Make Composite command. Z Project (Sum) will then create a multichannel 32-bit composite color stack.

-wayne

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