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Author Topic: Luminosity curves  (Read 5343 times)

David Mantripp

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Luminosity curves
« on: March 20, 2015, 03:46:35 PM »

Just trying to get back to grips with C1, after last using it at v3.8. Does it really not have a way to apply curves / levels to luminance/luminosity, but just to RGB? If not, what workarounds do people use to avoid ugly colour shifts?  I'm trying to find the way forward from Aperture ... Seems all alternatives have gotchas :-(
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BartvanderWolf

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Re: Luminosity curves
« Reply #1 on: March 21, 2015, 08:45:01 AM »

Just trying to get back to grips with C1, after last using it at v3.8. Does it really not have a way to apply curves / levels to luminance/luminosity, but just to RGB? If not, what workarounds do people use to avoid ugly colour shifts?

Hi David,

Since there are no other takers, which ugly colour shift? Capture One handles e.g. changes in Brightness quite gracefully, even if you want to use the Levels and Curves adjustments for that, instead of the Exposure and High Dynamic Range controls (which were significantly improved in Version 8). I'm not 100% sure (never saw the need to reverse engineer its behaviour), but it could be that the Levels adjustments are done at a very early stage of the Raw conversion, maybe even before gamma is applied. Curves adjustments can of course be more targeted, and there are Local adjustment layers available to tweak local colors (including the powerful Color Editor tool) to your heart's content.

Cheers,
Bart
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David Mantripp

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Re: Luminosity curves
« Reply #2 on: March 21, 2015, 09:39:24 AM »

Hi Bart,

Well, say I have a grey cloudy sky, and I want to add a contrast curve to bring out the structure. If I do this in C1 using the curves tool, I get structure, but I also get blue clouds... If I do the same thing in Aperture, or Iridient, or indeed Photoshop, I can set the curve to operate on luminosity, not RGB, and the outcome is largely neutral.

I can reduce this shift using other tools, but it gets quite complex. Note, i generally start with a neutral conversion, not film curve, so it's not as if I'm pushing things too far. In any case, I'm not a fan of the high contrast, saturatd look, I'm talking about fairly light adjustments here.

Seems a pretty basic thing... I must be missing something?

David
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Paul2660

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Re: Luminosity curves
« Reply #3 on: March 21, 2015, 04:49:59 PM »

Hello David,

I agree the curves tool in C1 is a bit dated, and limited, at least for my workflow.  You could try isolating parts of the image like your sky with a local adjustment.  Here C1 adds a lot of power to the user.  You don't have a curves tool (which is needed) in local adjustments, but you can control a lot of other features, that might help.  The WB was added to the local adjustments tools set in Vr 8 and it's very helpful to me with correcting color casts.

I find now with both LR an C1, I do as much as can with their tool sets, as they are now so powerful, I only wish the auto mask in C1 was as easy and accurate as the auto mask in LR.  C1's color editor is an excellent tool and can be used in a local adjustment layer, just make sure local adjustment layers don't overlap if you want to use the color editor as this seems to cancel out the effects.  Never has understood this, opened a case with C1, and they told me "that just the way it is".  You can have overlapping local adjustments and make WB adjustments in each and that won't effect the colors.

You can have 15 adjustment layers in C1's latest version of 8, and unlike LR, you can turn off individual layers to see their effects.  As far as can tell in LR at least for now, turning off adjustment masks created with the adjustment brush is all on or all off.  

I don't think you can set a adjustment layer in C1 to luminosity, like in CC, but they are still very helpful.

Paul
« Last Edit: March 21, 2015, 04:52:26 PM by Paul2660 »
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Paul Caldwell
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Jimmy D Uptain

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Re: Luminosity curves
« Reply #4 on: March 22, 2015, 12:20:01 PM »

Hi Bart,

Well, say I have a grey cloudy sky, and I want to add a contrast curve to bring out the structure. If I do this in C1 using the curves tool, I get structure, but I also get blue clouds... If I do the same thing in Aperture, or Iridient, or indeed Photoshop, I can set the curve to operate on luminosity, not RGB, and the outcome is largely neutral.

I can reduce this shift using other tools, but it gets quite complex. Note, i generally start with a neutral conversion, not film curve, so it's not as if I'm pushing things too far. In any case, I'm not a fan of the high contrast, saturatd look, I'm talking about fairly light adjustments here.

Seems a pretty basic thing... I must be missing something?

David

In this particular scenario, I would draw a mask on the clouds and use the clarity tool to bring out the structure.Then either reduce the saturation of the mask, or use the color edit tool to just reduce the blues.
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David Mantripp

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Re: Luminosity curves
« Reply #5 on: April 10, 2015, 04:36:20 PM »

In this particular scenario, I would draw a mask on the clouds and use the clarity tool to bring out the structure.Then either reduce the saturation of the mask, or use the color edit tool to just reduce the blues.



Well yes, but it seems odd to even need to do this. The concept of luminosity curves is hardly new. Photoshop has had it since Jurassic times. Aperture has it. Iridient has it (and LAB curves too). I guess Lightroom has it.

Not a show stopper but a strange absence.
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jrp

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Re: Luminosity curves
« Reply #6 on: April 11, 2015, 01:59:14 PM »

No, Lightroom doesn't have it; increasing contrast increases saturation, generally speaking. So far as I can tell, the Adobe guys have left it like this because they reckon that it gives a more pleasing result, much of the time.
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