Stacking/merging to increase brightness of highlights

sirch

sirch

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Following my first foray into Astro photography I was pondering if it is possible to stack a set of images so that the bright parts (in this case stars) get brighter without the rest of the image changing?
 
Thanks but looking at the feature list it doesn't seem to offer much that is different from enfuse and photoshop. What I had in kind was something that essentially did an image align and then added bright pixels without brightening "backgound" pixels. Might be tempted to have a go at writing something myself
 
Wouldn't increasing both brightness and contrast do the same thing?



Steve.
 
StarStax is for creating star trails using multiple long exposures. Take a look at RegiStax 6 as I think this will be what your looking for.
 
Steve Smith said:
Wouldn't increasing both brightness and contrast do the same thing?
Click to expand...

To some extent but it would not merge a stack, I did try this but I am not looking to increase overall brightness as that increases light pollution...

Brian_of_Bozeat said:
IIRC, photoshop layers with the "lighten" method only show the brightest pixels from each layer.
Click to expand...

Thanks for the video, there are lots of options for choosing the brightest pixel in the stack but what I was looking for was effectively to sum only the bright pixels, hence brighten the stars but not the background or light pollution. So I don't what the brightest value for every pixel, only for the "bright" pixels. I suppose something like a threshold so that only "white" pixels get enhanced, the rest remains the same or even gets dimmer.

Thinking about it perhaps one way (although not using a stack necessarily) would be to create a layer of only the sky/stars, convert that to mono, crank up the brightness and then merge that with the original.


MartinCornwall said:
StarStax is for creating star trails using multiple long exposures. Take a look at RegiStax 6 as I think this will be what your looking for.
Click to expand...

Thanks, looks interesting it is not obvious from the web page what it does, I'll download it and have a go.
 
If the terms brightness and contrast are used correctly, brightness affects the black level, contrast the peak level.

You could adjust the contrast to brighten the peaks, then adjust the gamma to lower the midtones and shadows.

However, you'd want to avoid clipping and work in linear light, not sRGB Gamma.
 
Thanks @st599 I've never really done anything with gamma adjustments (at least not knowingly), I'll have a go.
 
sirch said:
Thanks for the video, there are lots of options for choosing the brightest pixel in the stack but what I was looking for was effectively to sum only the bright pixels, hence brighten the stars but not the background or light pollution. So I don't what the brightest value for every pixel, only for the "bright" pixels. I suppose something like a threshold so that only "white" pixels get enhanced, the rest remains the same or even gets dimmer.
Click to expand...

If a curves adjustment doesn't provide enough precision in targeting just the bright bits you're after then Layer styles | Blend if allows you to select the range of tones affected by any given layer.

So you could adjust the highlights using a duplicate layer lighten or screen blend modes, or a curves adjustment, or image statistics, and use with 'blend if' accordingly.

An alternative approach would be to use luminosity masks.
 
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