Antlia Triband Ultra Processing

Jeramie Shuler

Greetings- 

I shoot with a 2600 OSC and my typical workflow is WBPP, Crop, DBE, BlurX, NoiseX, and then into stretching. Recently I noticed that while attempting to stretch an image I see that the color "peaks" in the histogram are all separated with gaps between the red, green, and blue where I would typically see the peaks aligned with one another. I believe that what I am seeing is how the filter actually "works" and closely follows the spectrum curve for this filter. 

My questions are the following:

1. Can someone confirm that what I'm seeing with the separation in the channel peaks is caused by the filter, or is there a missing data calibration step that is causing this?
2. I'm assuming that if the triband ultra filter is creating those discrete channels, I should treat the data differently than I would unfiltered OSC data. If so, is there a specific workflow that I should follow to properly work with this data? Would you potentially use a NB workflow? 

Many thanks for any guidance on this.

J

Jeramie Shuler

Here's what I'm talking about with the separation between the peaks:

BlockHead

When you are using a narrowband filter you are observing (letting through) only particular wavelengths of light. So when you look at the histogram of an image that shows each of these wavelengths (since you are using a triband filter) you will see the information at each of these positions in the spectrum. If they lined up... that would be very bad! 

This situation is different than looking at continuum imagery (broadband images) where the SKY values are generally equal in signal of all colors- that is the sky is generally neutral (except in light pollution or if the moon is in the sky). Removing the bias of the sky brightness in each color results in a neutral sky color. That is why you do the alignment.

This is also done with NB images as well... no one wants a bias in the sky color. However, NB images will not likely have anything like these aligned sky values since you are looking at very particular wavelengths with filters that have very different transmission values. 

What you are seeing is normal physics.

-the Blockhead 

Jeramie Shuler

Many thanks. 

So, I was correct on my first assumption. 

Is there a specific workflow you would recommend to process OSC data with a triband filter? 

J

BlockHead

Not the moment. This isn't an area of expertise for me right now.

-the Blockhead