M31 PI failed colour calibration.WHY?

[Daniel-K]

Hi just spent 2 hours processing in PI and came to try and get some colour out of my image and theres is nothing there! the only thing i can think of is the colour calibration failed is there anything i can do at this stage to get it back on track or do i need to star again.

Dan

[andrewluck]

It's probably not the colour calibration as this will only make adjustments to colour balance, not completely desaturate the image.  There's an case for saving the image at various points during processing to make it easier to revert to a previous version.

Any non-linear stretch will reduce the colour so once you've made the initial histogram stretch then increase the saturation, either through the Saturation or Curves tool.

Cheers

Andrew

[Daniel-K]

ok thanks i shall give that a try

[sharkmelley]

The Andromeda Galaxy needs a huge amount of stretching, which is why you are seeing this.  Christian Buil's free IRIS software has the wonderful arcsinh (hyperbolic arcsine) function that allows an incredible amount of stretching whilst preserving the original RGB balance of the astronomical data i.e. it doesn't "bleach" star colours to become white.  It's a shame that PI doesn't have this as part of its basic toolkit.  Photoshop has the same problem which is why folk end up resorting to star masks to protect star colour or to "fudge" it back in afterwards.  I'm sure there are lots of other workarounds but in my opnion the best approach is not to destroy the colour in the first place!

Mark

[Daniel-K]

i tried adding in the saturation at various stages last night but ended with the same result, this is the same data bu processed in CS6 it was alot easier to get the colour in cs6

[sharkmelley]

That's looking miles better!  Did you have to do anything special in PS6 when applying the stretching?

Mark

[Daniel-K]

no i just feel i have lost detail with doing it in CS6 i want this colour from the PI processing but i just cant get it when i use the colour saturation tool or the stretching  tool only the background seems to get a dose of the saturation.   

[Daniel-K]

still not right but got some colour. heading in the right direction i hope