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Finding the Luminosity of a single pixel

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  #11  
Old 11-28-2013, 11:24 AM
skoobey skoobey is offline
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Re: Finding the Luminosity of a single pixel

Quote:
Originally Posted by milesburden View Post
There's some mixed responses here. I'll answer them individually:

Gry: Thanks for your input, it's much appreciated. I'm a big fan of your work!

Klev & Scooby: The reason I wanted to know how to determine individual luminance levels was twofold, I'm currently spending a lot of time (like most of you I expect) playing about with colour adjustments and I've grown incredibly fond of luminosity masks but wanted to have more control over the range that is selected. It's not a specific problem as such but an experimental technique. Say theres a particular luminance range or even a specific range within an object in an image that I wanted to play a blue through. From the useful input I've had on this thread I can now sample some pixels across that item and get a luminance range for it. I now know what values to target with my blend if sliders or can create a mask of that desired range. Why that's baffling to some of you I'm not sure?

Skooby; I was experimenting, trying to create a mask in a manner I hadn't done before, how else am I expected to learn if I don't experiment/ask? I did this with different methods, once by splitting the sliders and another without, I played with the blend modes also. It targeted the range I wanted, and I can adjust the mask if it's too harsh. No need to snigger. I'm fully aware that you can create masks with channels, and numerous other methods. I just wanted to try/learn a different technique.

Miles
If you want to colorize a specific tonal range, you can do that by a gradient mask, then use blending modes (making transparent parts of the gradient is a great way to avoid masking, or at least most of it).

I thought you had a specific task at hand, so I wanted to learn more form you, not discourage you.

It can definitely be a good way to do masking without going into actual pixels, only adjustment layers.
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  #12  
Old 11-28-2013, 12:12 PM
milesburden milesburden is offline
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Re: Finding the Luminosity of a single pixel

Seems I misinterpreted the nature of your response and jumped the gun, apologies for that.
By gradient mask do you mean a black and white gradient map masking the specific tones required or am I lost?

Miles
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  #13  
Old 11-28-2013, 05:34 PM
skoobey skoobey is offline
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Re: Finding the Luminosity of a single pixel

"Say theres a particular luminosity range or even a specific range within an object in an image that I wanted to play a blue through"

You make a blue color sample in a gradient map, make the other to samples transparent, and adjust it's position. Blend as you wish.
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  #14  
Old 11-29-2013, 03:43 AM
milesburden milesburden is offline
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Re: Finding the Luminosity of a single pixel

Hi Skoobey, sorry I got lost by the term 'gradient mask' as opposed to 'gradient map'. That makes perfect sense, and would skip a few unneeded steps. I'll spend a little more time thinking about the problem before asking a question in future as that solution now seems bloody obvious. Thanks for your help.


Miles
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  #15  
Old 11-29-2013, 07:30 AM
skoobey skoobey is offline
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Re: Finding the Luminosity of a single pixel

I'm so sorry. Yes, GRADIENT MAP.
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  #16  
Old 11-29-2013, 10:18 AM
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andrewrodney andrewrodney is offline
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Re: Finding the Luminosity of a single pixel

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Originally Posted by klev View Post
It seems I'll never understand some of these requests. Why would you want to know a sample from one pixel on a regular basis? Noise, rounding during interpolation, etc. render such a measurement not very interesting. Was it a strand of hair or something like that? Even then the results may not be as you expect.
Amen to that comment.
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