Understanding wipe/auto dev

[BrendanC]

Hi again,

Yes, it's another question!

I don't understand how Auto Dev, Wipe, then Auto Dev works.

If I open my image (FITS, stacked in DSS, captured from modded EOS1000D, selecting 'Linear, from OSC/DSLR with Bayer matrix and not white balanced', and apply Auto Dev, I get this:

5.jpg (164.44 KiB) Viewed 2509 times

I then go through binning and cropping, and then get to Wipe. More often than not, wipe seems to do fairly drastic and unpredictable things to my image. This isn't a bad example, I've had worse:

1.jpg (186.42 KiB) Viewed 2509 times

However, when I 'Keep' the image, I get a message I don't understand. It says 'Please check color result. Compose mode is engaged. Luminance and colour are being processed separately and in parallel. Use the Color button to evaluate the effect of the Wipe module on your color data as well.'

If I keep the image, it goes back to how it looked before I applied Auto Dev! Like this:

3.jpg (50.83 KiB) Viewed 2509 times

So, questions are:
* Should wipe have such a dramatic effect?
* What does that message mean?
* What does it mean about using the Color button? Is it referring to the Color module towards the end of the sequence?
* How can I evaluate the effect of Wipe (ie what should I be looking for to evaluate it)?
* Why can't I change the mode?
* Why, after Keeping the wiped image, does it revert to pre-Auto Dev?
* What do I do after all this? Should I use Auto Dev again? If so, should I re-do the stretch, or use the image as-is?

Sorry, that's a lot of questions. But then again, I've been trying for some months to get my head around StarTools and I'm not sure I'm succeeding.

Thanks, Brendan

[admin]

Hi Brendan,

So, questions are:
* Should wipe have such a dramatic effect?

Yes.
The stretch in Wipe is designed to - continuously - show you defects in your background. It completely discards any previous stretch.

* What does that message mean?

It's hard to explain without just re-wording what the message says.
Detail and color is processed separately (yet simultaneously) while Compose mode is on. In essence you are seamlessly processing two datasets at the same time. This allows the processing engine make different decisions for your coloring and different decisions for your detail. This notion of separating luminance and color is standard fare for people doing, for example, LRGB composites. In years past, it has been common/recommended practice to process L (luminance/detail) and RGB (color) separately in sequence and then combine them at the very end (this practice remains so in other software). Even DSLR datasets can now benefit from the enhancement in signal fidelity and color presentation that this novel way of working brings (see also here); for non-white balanced DSLR datasets, the green channel is more reliable than the red or blue channels (a Bayer matrix has twice the amount of green samples vs blue and red). Re-weighing the luminance signal to reflect that allows you to process a cleaner luminance signal, while retaining the color data as-is.

* What does it mean about using the Color button? Is it referring to the Color module towards the end of the sequence?

The message is referring to the Color button in the top right corner.

* How can I evaluate the effect of Wipe (ie what should I be looking for to evaluate it)?

It is probably best to consult the documentation and videos.
In good, properly calibrated datasets, you should only have to worry about the removal of gradients.

* Why can't I change the mode?

If your are not processing an RGB image, but rather are processing luminance and color separately, the different modes are not applicable.

* Why, after Keeping the wiped image, does it revert to pre-Auto Dev?

Removing gradients, vignetting, etc. completely and drastically reconfigures the dynamic range your signal occupies (e.g. there is no longer need to allocate dynamic range to the useless gradients, it is now freed up for describing true celestial signal). Any prior stretch will no longer be suitable.

* What do I do after all this? Should I use Auto Dev again? If so, should I re-do the stretch, or use the image as-is?

Indeed, many/most workflows you will find in tutorials, videos and workflow charts will see you re-do your stretch (for the reasons outlined above).
See here for a very useful, succint workflow chart by J. Scharrman if you are not quite across what follows what, or what each step does.

Hope this helps!

[BrendanC]

Thanks for taking the time to provide such a comprehensive reply Ivo.

I'm still having difficulty with the flow of this process, but let's see if this starts working for me.

I do appreciate that you've provided a lot of help, support, tutorials etc.