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Old 19-01-2014, 10:11 PM
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CIELAB colour space

I have recently discovered the joys of processing in the CIELAB (L*a*b*) colour space. I have mainly been using it for tweaking of colour and colour intensity, but I have also developed some more specific techniques that rely on it, e.g. for fixing coloured star haloes and transplanting RGB stars into a narrowband image.

Jay GaBany included LAB manipulation as one of the (ten?) techniques for colour enhancement in his AAIC 2013 talk. He mentions it again in the "Lessons from the Masters" book and the section by Adam Block in the same book includes a couple of pages on using LAB in Photoshop for adjusting galaxy colour. Apart from this I haven't seen it mentioned much in the astro context.

Is anybody else using LAB in their processing?

Cheers,
Rick.
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Old 20-01-2014, 05:58 AM
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Yes Rick, I've been using LAB for years on my astro shots.
Love the fine control it gives.

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Old 20-01-2014, 08:46 AM
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The only technique I have used was to control colour noise with blurring of the appropriate channel in LAB. But other approaches seemed more flexible so tend not to use it.

We never got those talks from AAIC. I didn't take notes because I figured I could go over them later in the downloads.

Greg.
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Old 20-01-2014, 09:20 AM
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Yes Rick, I've been using LAB for years on my astro shots.
Love the fine control it gives.

Thanks, Andrew. There's a lot to be said for decoupling lightness from colour. Quite a few of the PixInsight processes use LAB behind the scenes and have an option to operate on the L channel only.

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Originally Posted by gregbradley View Post
The only technique I have used was to control colour noise with blurring of the appropriate channel in LAB. But other approaches seemed more flexible so tend not to use it.

We never got those talks from AAIC. I didn't take notes because I figured I could go over them later in the downloads.

Greg.
Greg, the chapter by Jay in the Lessons from the Masters book covers pretty much all the stuff he talked about in his first AAIC talk but it is a shame we haven't seen the rest of the presentations online yet.

I have found a few things that I can do in LAB that are much more difficult to do in any other way. I'm reading a Photoshop book, Photoshop LAB Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace at present. I'm hoping to pick up a few new techniques that I can transfer across to PixInsight.

Cheers,
Rick.
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Old 20-01-2014, 10:45 AM
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I'm reading a Photoshop book, Photoshop LAB Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace at present. I'm hoping to pick up a few new techniques that I can transfer across to PixInsight.

Cheers,
Rick.
Yep Rick, I'm pretty sure that's the book I was reading when I first started using LAB techniques in PS.

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Old 20-01-2014, 11:10 AM
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I have found a few things that I can do in LAB that are much more difficult to do in any other way. I'm reading a Photoshop book, Photoshop LAB Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace at present. I'm hoping to pick up a few new techniques that I can transfer across to PixInsight.

Cheers,
Rick.[/QUOTE]

Sounds good Rick. I am always wanting to learn new software processing approaches.

Greg.
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Old 20-01-2014, 11:16 AM
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Yep Rick, I'm pretty sure that's the book I was reading when I first started using LAB techniques in PS.

It's a good book so far, Andrew. A bit slow to start but I suppose colour spaces are a mystery to a lot of folks and the basics have to be covered.

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Sounds good Rick. I am always wanting to learn new software processing approaches.

Greg.
I'll report back on anything interesting that I pick up, Greg.

Cheers,
Rick.
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Old 20-01-2014, 12:11 PM
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I use LAB colour on every image at some stage.
I like the way it boosts the colour without changing the brightness.
It also allows very fine adjustments of tone.
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Old 21-01-2014, 09:28 AM
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LAB is one of those things that comes into style and then goes out of fashion and then comes back again!

Haven't played with it for a while myself.

H
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Old 21-01-2014, 09:46 AM
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LAB is one of those things that comes into style and then goes out of fashion and then comes back again!

Haven't played with it for a while myself.
Not for me, I use it whenever I need to and for me it's a great way in getting what I want out of my images.
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Old 21-01-2014, 12:31 PM
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Thanks for the feedback Allan, H and Andrew. I think that some processing in LAB will be a permanent part of my workflow.

Cheers,
Rick.
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Old 21-01-2014, 02:21 PM
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Thanks for the feedback Allan, H and Andrew. I think that some processing in LAB will be a permanent part of my workflow.

Cheers,
Rick.
Thanks Rick,
I actually learnt about it from Louie.
see here:

http://www.youtube.com/watch?v=fE2GS_87Ct8


cheers
Allan
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Old 21-01-2014, 03:20 PM
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Of course!

My experience: I rely on the histogram for processing my landscape images (identifying tonal regions). Once converted to Lab and then back to Adobe RGB, the histogram gets shot -- everything ends up as quantized data in the midtone regions, which makes it very hard to work when trying not to clip data.

Admittedly, I've never used it for astrophotography.

H

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Not for me, I use it whenever I need to and for me it's a great way in getting what I want out of my images.
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Old 21-01-2014, 04:15 PM
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Once converted to Lab and then back to Adobe RGB, the histogram gets shot -- everything ends up as quantized data in the midtone regions, which makes it very hard to work when trying not to clip data.

Admittedly, I've never used it for astrophotography.

H
Doesn't sound right, if that's what you get then I don't blame you for not using it.
I've never found this to be the case though and I like using it, it's not a 'style' that comes and goes for me.
I'd recommend people look into it, I'm sure there's tuts online or the book that Rick mentioned is a great start.

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Old 21-01-2014, 05:33 PM
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I have used LAB in non astro images a bit, it gives you a few more options so I would be interested to see what it offers for astro.

Brett
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Old 21-01-2014, 07:05 PM
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I have used LAB in non astro images a bit, it gives you a few more options so I would be interested to see what it offers for astro.
G'day Brett,

Uses I have found so far are intensifying colour (as per the video tutorial from Louie that Allan posted above), modifying colour (tweaking that cyan galaxy to make it look more blue, etc.) and a host of applications for operating on lightness or colour independently. A good example of this is incorporating RGB star colours in a narrowband image by merging the a and b channels through a star mask but leaving L unmodified so that the star profiles don't change.

Cheers,
Rick.
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Old 03-02-2014, 07:05 PM
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G'day Brett,

Uses I have found so far are intensifying colour (as per the video tutorial from Louie that Allan posted above), modifying colour (tweaking that cyan galaxy to make it look more blue, etc.) and a host of applications for operating on lightness or colour independently. A good example of this is incorporating RGB star colours in a narrowband image by merging the a and b channels through a star mask but leaving L unmodified so that the star profiles don't change.

Cheers,
Rick.
Good post.

Many people will already know this:

I find when processing that you have to separate the idea of brightness & colour
& always be thinking of one or the other.
LAB mode allows you to do that.
You can wreck an image by turning up the brightness to increase the colour. (with curves)


It is sometimes hard to process without damaging the stars.
Another great idea is to get rid of the stars from nebulas using this trick in a Photoshop tutorial:

http://www.astro-photography.net/Star-Removal.html

Note - if I press delete on PS CS5 it doesn't work as per the tutorial.
I just need to select the stars & click: edit, fill.
The stars magically disappear.
(If some are still there you can use the healing brush tool to get rid of them.)

They can then be copied & pasted back in later from a partially stretched
version that was saved on your HDD.
That way they remain undamaged & still have colour.

cheers
Allan
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