The Develop and Contrast modules seem to do a good job stretching my images but the fainter nebulosity seems a little dull.
I am used to stretching with an S curve in photoshop to target the fainter nebulosity without brightening the stars so much.
Is there a method to adjust the apparent slope in the Develop or Contrast modules, or am I completely on the wrong track.
Any help would be appreciated, while I am getting good results with StarTools I feel I could get a little more of the faint stuff.
Ken
How to bring out faint nebulosity
Re: How to bring out faint nebulosity
Hi Ken,
What you're after is the HDR module, specifically its 'Brighten Dark' algorithm (but do experiment with the other settings and algorithms!). Use the Dark/Bright Response to vary the response of dark detail to the enhancement.
As you've discovered, StarTools has a bit of a different approach to stretching your signal. StarTools makes a clear distinction between 'global' (what you're used to in Photoshop) and 'local' (which is what the Contrast, HDR and Sharp modules do).
Whereas a global histogram stretch (for example with an S-like curve) affects the whole image, a local stretch applies varying degrees of stretching based on local characteristics of the image.
Therefore in StarTools, a global histogram stretch is considered 'just the beginning' and further detail is teased out using the Contrast (medium-large scale local manipulation), HDR (medium-small scale local manipulation) and Sharp modules (medium-small inter-scale and noise aware local manipulation).
Depending on the quality of your data, also do not dismiss the AutoDev feature. As of 1.3.5 it has become my preferred way of performing global stretching bar none, often needing very little (or none!) further refinement in the Contrast/HDR or Sharp modules. If AutoDev has reasonably reliable information at its disposal and it may assume that any noise in the image is random in nature (NOTE: be careful with debayered images from OSCs and DSLRs - the interpolation process will have introduced non-random artifacts due to noise), then AutoDev will be very adept at calculating a global stretch that brings out all detail as effective as possible. A Region of Interest can further help AutoDev home in on the detail that you find the most interesting.
What you're after is the HDR module, specifically its 'Brighten Dark' algorithm (but do experiment with the other settings and algorithms!). Use the Dark/Bright Response to vary the response of dark detail to the enhancement.
As you've discovered, StarTools has a bit of a different approach to stretching your signal. StarTools makes a clear distinction between 'global' (what you're used to in Photoshop) and 'local' (which is what the Contrast, HDR and Sharp modules do).
Whereas a global histogram stretch (for example with an S-like curve) affects the whole image, a local stretch applies varying degrees of stretching based on local characteristics of the image.
Therefore in StarTools, a global histogram stretch is considered 'just the beginning' and further detail is teased out using the Contrast (medium-large scale local manipulation), HDR (medium-small scale local manipulation) and Sharp modules (medium-small inter-scale and noise aware local manipulation).
Depending on the quality of your data, also do not dismiss the AutoDev feature. As of 1.3.5 it has become my preferred way of performing global stretching bar none, often needing very little (or none!) further refinement in the Contrast/HDR or Sharp modules. If AutoDev has reasonably reliable information at its disposal and it may assume that any noise in the image is random in nature (NOTE: be careful with debayered images from OSCs and DSLRs - the interpolation process will have introduced non-random artifacts due to noise), then AutoDev will be very adept at calculating a global stretch that brings out all detail as effective as possible. A Region of Interest can further help AutoDev home in on the detail that you find the most interesting.
Ivo Jager
StarTools creator and astronomy enthusiast
StarTools creator and astronomy enthusiast
Re: How to bring out faint nebulosity
Thanks Ivo,
As a Newbie I had down loaded the stable version 1.3.3.224, I have now installed the 273 version and the added controls will take a while to understand.
However I have reworked some images following your advice with significant improvement.
I stack with DSS and was not sure of the settings I should be using, but have just rad another post where you have explained that.
I will restock and try again.
Thanks again
Ken
As a Newbie I had down loaded the stable version 1.3.3.224, I have now installed the 273 version and the added controls will take a while to understand.
However I have reworked some images following your advice with significant improvement.
I stack with DSS and was not sure of the settings I should be using, but have just rad another post where you have explained that.
I will restock and try again.
Thanks again
Ken