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Author Topic: histogram and adjustment for only part of an image  (Read 209 times)

bwana

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histogram and adjustment for only part of an image
« on: February 05, 2019, 09:57:08 AM »

When I am adjusting an image with the levels tool (that graph that is a straight line where you can add bezier points and bend parts of it up and down), I sometimes only want to apply these corrections to a part of an image. Although I could use the gradient tool in lightroom and then drag the sliders to achieve changes, the histogram then changes but it is reflecting ALL the luminance values of the entire image.  If I want to edit clouds for example, I would use the circular mask tool to cover a cloud and then adjust. And although the histogram will show me what's clipping, I would like to get a sense of the specific range of tonal values in the cloud and how they are changing. In photoshop I could even get more refined and specify which luminance values I want to change (luminosity mask), But I still just use the eyeball. Then when I print, I have to 'remember' what the adjustments looked like on screen for the region I adjusted. If I had a histogram, it would help me be more quantitative and reproducible. Is there an application or technique that would allow this?
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nirpat89

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Re: histogram and adjustment for only part of an image
« Reply #1 on: February 05, 2019, 11:54:19 AM »

When I am adjusting an image with the levels tool (that graph that is a straight line where you can add bezier points and bend parts of it up and down), I sometimes only want to apply these corrections to a part of an image. Although I could use the gradient tool in lightroom and then drag the sliders to achieve changes, the histogram then changes but it is reflecting ALL the luminance values of the entire image.  If I want to edit clouds for example, I would use the circular mask tool to cover a cloud and then adjust. And although the histogram will show me what's clipping, I would like to get a sense of the specific range of tonal values in the cloud and how they are changing. In photoshop I could even get more refined and specify which luminance values I want to change (luminosity mask), But I still just use the eyeball. Then when I print, I have to 'remember' what the adjustments looked like on screen for the region I adjusted. If I had a histogram, it would help me be more quantitative and reproducible. Is there an application or technique that would allow this?

A little confusion....

The graph like tool - are you sure you are talking about Levels and not Curves.  The former should look like a histogram.

Are you using Lightroom or Photoshop?  You are going back and forth and it is not quite clear to me what your question relates to. 

If it is Photoshop (I don't know about Lightroom): if you make a selection, the histogram will reflect the property of the selection only and not the whole image.  So if you want to work on the clouds, select them, the standalone histogram will take into account only the clouds.  Now if you make an adjustment layer (be it Levels or Curves,) it will use the selection to make a mask for that layer.  The selection gets automatically deselected at that point and the histogram will reflect the whole image.  Then do Selection > Reselect.  This will take the histogram back to representing only the selected pixels.  Do your adjustment and deselect when satisfied.  Similarly any mask (gradient, luminosity, etc.) can be also reselected by simply right-clicking the layer mask and selecting "Add Mask to Selection."


:Niranjan.
« Last Edit: February 05, 2019, 08:00:40 PM by nirpat89 »
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bwana

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Re: histogram and adjustment for only part of an image
« Reply #2 on: February 05, 2019, 12:15:39 PM »

thank you. I am using lightroom. My discussion of photoshop only refers to what I know from reading and I do not really use it. I guess I need to spend time in it. It seems to be able to do what I want based on your clear reply.
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mcbroomf

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Re: histogram and adjustment for only part of an image
« Reply #3 on: February 05, 2019, 12:43:17 PM »

PS will do exactly what you want.  You are referring to the curves tool not levels, but using any adjustment tool in PS that creates a layer over the image you can then apply a mask to the curve/tool, eg so that the adjustment will only apply say, to the cloud are you have painted into the mask.  You can then turn the adjustment layer on/off and see what change it's having on the histogram.

If you subscribe to LuLa I can strongly recommend the interviews Kevin did with Charles Cramer last year.  Charlie uses this technique for much of his own post process local adjustments.  If you're not a subscribed it's worth joining (IMO) just for these.
https://luminous-landscape.com/videos/master-charles-cramer/
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digitaldog

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Re: histogram and adjustment for only part of an image
« Reply #4 on: February 05, 2019, 12:44:10 PM »

thank you. I am using lightroom. My discussion of photoshop only refers to what I know from reading and I do not really use it. I guess I need to spend time in it. It seems to be able to do what I want based on your clear reply.
In Photoshop, the selected area is what you'll see from a Histogram but that's not the case in Lightroom; it is the entire image.
As for Histogram info in general:

Everything you thought you wanted to know about Histograms
Another exhaustive 40 minute video examining:

What are histograms. In Photoshop, ACR, Lightroom.
Histograms: clipping color and tones, color spaces and color gamut.
Histogram and Photoshopís Levelís command.
Histograms donít tell us our images are good (examples).
Misconceptions about histograms. How they lie.
Histograms and Expose To The Right (ETTR).
Are histograms useful and if so, how?


Low rez (YouTube): http://www.youtube.com/watch?v=EjPsP4HhHhE
High rez: http://digitaldog.net/files/Histogram_Video.mov
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Andrew Rodney
Author ďColor Management for Photographers"

Rand47

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Re: histogram and adjustment for only part of an image
« Reply #5 on: February 05, 2019, 06:49:08 PM »

thank you. I am using lightroom. My discussion of photoshop only refers to what I know from reading and I do not really use it. I guess I need to spend time in it. It seems to be able to do what I want based on your clear reply.

Since you clarify that youíre using Lightroom, Iíll chip in.  While curves adjustment layers with masks in Photoshop is probably the most flexible and direct way to achieve what youíre after, you can also get a ďa lot of the way thereĒ in Lightroom.  Using your cloud example, use the paintbrush tool to create a selection that includes your clouds.  Then use the range masking tool to narrow your selection to clouds (luminosity range masking most likely for clouds).  You can then use a combination of tools;exposure, clarity, blacks, whites, contrast, etc. to take your selection in a lot of useful directions.  Iíll often neutralize all of the sliders, and then turn on the visibility of the selection (the O key toggles) and create the selection first.  Then when Iím happy with the selection, Iíll start to tweak it.

This approach is a sort of kluge, but youíll be surprised at how well it can work as a ďfakeĒ selective curves adjustment.

I posted a query recently wondering why Adobe hasnít given us true layers and curves in the targeted adjustment tools.  That would be slick.

If youíre a member here, check out the Masters videos w/ Charles Cramer.  He uses curves adjustment layers/masks to great effect in Photoshop.  The videos are very instructive.
Rand
« Last Edit: February 05, 2019, 06:53:45 PM by Rand47 »
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Rand Scott Adams
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