Bolton Astronomical Society

IRIS processing and green nebulae
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Author:  ESwarbrick [ Mon Feb 08, 2016 10:08 pm ]
Post subject:  IRIS processing and green nebulae

Hi, calling the IRIS workers........
I have an ongoing problem with IRIS and DSLR processing (Canon 600D full spectrum).
All the stages go OK until CFA conversion; the background becomes magenta and any nebulosity is almost white. Using the Equalisation command neutralises the background (sort of), but the nebula then becomes bright green. Each 'light' has this colour after CFA conversion to RGB. Photoshop confirms these colours so it's not a function of IRIS display. This has happened every time I try to use IRIS. IRIS Settings is told that my camera is a 500D from the limited choice. Binning makes no difference and processing in DSS and Regim is OK.
I hope somebody can throw some light (pun intended) on this problem.

Author:  rwilkinson [ Tue Feb 09, 2016 9:26 am ]
Post subject:  Re: IRIS processing and green nebulae

I hope that one of the Canon users will give you a definitive answer on this, but in the meantime, here are my suggestions:

First, check the date-stamp on the libdcraw.dll file in your /IRIS folder, and if it's earlier than September 2014, then replace it with the latest version, downloaded from here:

If this doesn't fix it, then try the setting for the Canon 50D.

If you call me on Skype I could talk you through this using the Share Screens facility.

Author:  DRatledge [ Tue Feb 09, 2016 9:39 am ]
Post subject:  Re: IRIS processing and green nebulae

I take it you are following the A4 sheet?

At CFA stage then colour appears for the first time. These are digital images made up of numbers. Saying the nebula is "white" doesn't really mean anything - by moving the screen stretch (threshold) sliders then we can get anything or everything white. Colours too will change as we move them up and down. It's worth taking time to get familiar with these sliders.

What really counts are those numbers. Move the cursor over the image and see what numbers you are getting - displayed bottom right. Move your cursor over the nebula. What are its numbers i.e. its brightness. Your camera should have 16000 as a maximum. If the nebula is reading 16000 then it really is white.

After CFA conversion the next stage is alignment - stellar registration. Then stacking - add a sequence. Then we get to do the colour balance. Black is the next command followed by Colour Balance - I would guess for you using a UHC filter (?) then 1/1/1.8 will be about right. However that full spectrum mod you mention is a worry - you will need to block infra-red if this is the case so a UHC-CCD filter is really needed not the ordinary one.

Hope this helps - it is a steep learning curve but the A4 sheet of instructions will give you a good image. Yes more advanced techniques could improve it further but leave them till you have mastered the basics.

Author:  bchamberlain [ Wed Feb 10, 2016 11:04 am ]
Post subject:  Re: IRIS processing and green nebulae

I'm no expert Eb but I get weird effects sometimes if, before saving as a Tiff in Iris, I forget to do a 'clipmin 0 0' to remove the negative numbers which Iris uses

Author:  rwilkinson [ Wed Feb 10, 2016 5:03 pm ]
Post subject:  Re: IRIS processing and green nebulae -SOLVED

I've just been on Skype with Eb and we've found the solution - the CFA-matrix wasn't being decoded correctly - so the red parts of the image came out green and vice versa.

But we soon deduced that with his Canon 600D camera it's necessary to select the CANON 50D/5Dmk2/7D option in IRIS's Digital camera Model drop-down menu.
This renders the nebulae in their proper red colours, but left the sky background looking greeninsh - so he'll be using the White balance adjustment sliders to obtain the "magic numbers" to put into the RGB balance boxes.

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