FORUMS: list search recent posts

Help Selecting Lightness Ranges

COW Forums : Adobe Photoshop

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
George Stattin
Help Selecting Lightness Ranges
on Oct 13, 2009 at 7:04:33 am

How can I select pixels that fall within a specific lightness range? Note, what I am not trying to do is select all highlights or shadows or midtones (i.e. color range command). The idea is to restrict the selection to the pixels who's lightness values fall within 1 of 7 portions of the histogram, as pictured:



For example, I need to create a selection of pixels with lightness values between 188 and 225 (the "Lights" range), as in the picture below:



Return to posts index

John Mensinger
Re: Help Selecting Lightness Ranges
on Oct 13, 2009 at 1:29:25 pm

George, I can't see an image in your post, but what you want is a "luminance mask."

Typically, you can produce such a mask by loading a given channel as a selection. In the Channels panel, Ctrl+click on a channel thumbnail to load that channel as a luminance mask. Your image may already contain a channel that will produce a useful mask this way, but if it doesn't, choose the channel that's closest, duplicate it, then adjust its luminance range using Levels and/or Curves until it is suitable as a basis for your mask.


Return to posts index

John Mensinger
Re: Help Selecting Lightness Ranges
on Oct 13, 2009 at 2:01:50 pm

Ah! Found it. My original reply was the quick & simplified explanation.

This tutorial will really give you the weapons you need for masking and adjusting based on luminance and density:
http://www.deke.com/category/free-tags/luminance-mask


Return to posts index


George Stattin
Re: Help Selecting Lightness Ranges
on Oct 13, 2009 at 5:53:50 pm

Thanks John,

Yes, I'm trying to create a luminance mask, but a smart luminance mask if you will, that can be replicated via an action for any image. I happen to have already read Deke's book and am familiar with basic channel operations. Deke is the best, but his solution accomplishes precisely what I intend to avoid: selecting a range of lightness based on subjective appearance, with only one threshold: above #. For example, with his luminance mask the result will contain "all pixels lighter than #."

If it helps, I'm thinking along the lines of the Threshold adjustment. The problem is that the Threshold adjustment in Photoshop is also of the type, "select all pixels above #." Instead, I need to "select only pixels between # and #".

If you are able to see the pictures it would help a lot. My goal is to make an action that will create 7 Hue/Sat Adjustment Layers, each masked by one of the 7 lightness ranges, Shadows, Darks, Dark Mids, Midtones, Light Mids, Lights, and Highlights. So I must determine how to mask each lightness range with a command that is repeatable via action regardless of the characteristics of an image.

Here are the direct links to the images. The first shows the ranges I'm trying to accomplish, the second shows an example of selecting only one range while excluding all others (i.e. between 184 and 219). Note, any solution doesn't necessarily have to be based on numerical values, as long as it selects only a definable, contiguous percentage of the histogram.

http://img200.imageshack.us/img200/852/lightness.gif
http://img360.imageshack.us/img360/7442/howr.gif


Return to posts index

George Stattin
Re: Help Selecting Lightness Ranges
on Oct 13, 2009 at 6:49:23 pm

I've found a solution. It's surprisingly obvious :)

1. Add a Gradient Map Adjustment Layer going from black to white.

2. Add a Curves layer, map all input values to an output of 0. All pixels will turn black.

3. Still in curves, use the pencil to draw a short horizontal line (by clicking then shift clicking, or by carefully dragging) along the top of the graph, sending only the desired range to white (255).

4. Use the result to create a mask, use that mask to restrict a Hue/Sat Adjustment Layer.

5. Repeat 2-4 for each Hue/Sat layer (do not re-add the gradient map or curves layers). The layers created in steps 1 and 2 can be deleted afterward.

The resulting hue/sat layers will, theoretically, allow for awesome color control (at least as far as basic color corrections), surpassing standard commands available in Photoshop or Camera Raw. A similar method can likely be applied to Lab mode for ultimate color control.

Thanks for your time guys, I hope someone finds this useful someday :)


Return to posts index

John Mensinger
Re: Help Selecting Lightness Ranges
on Oct 13, 2009 at 7:39:54 pm

Wow! Very interesting.

It really is the range-targeted mask you originally sought.

I like the way you think, George. Thanks for sharing.

John M:
All of the vim with none of that annoying vigor.


Return to posts index

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
© 2017 CreativeCOW.net All Rights Reserved
[TOP]