Introduction to Luminosity Masks
Introduction to Luminosity Masks
In this article I want to introduce you to a Photoshop topic that has to some extent fallen from favour, primarily due to the superlative work that Adobe has done in Camera RAW and in Lightroom for managing images. In both offerings we find five areas of luminosity control, blacks, shadows, exposure (aka midtones), highlights and whites. For many photographic post processors these solve most issues. However, when you want much more granular control and image specific adjustments, we merely need to hop over to Photoshop to step up to the next level.
What is Luminosity
Luminosity is a fancy word that describes tone across an image. When we think in 8 bits, like our histograms, black is 0 and white is 255. Each pixel making up the image will have a luminosity value in that range, and each pixel only has one value at a time. The histogram shows us graphically how many pixels have that value, a great advantage, but to take our manipulation to the next level we want to be able to confine our adjustments to a specific luminosity range.
What is a Mask
In Photoshop parlance a mask controls the impact of an adjustment. Areas of a mask that are completely white pass the entire effect of the adjustment, like a clear sheet of acetate. Areas of a mask that are completely black block the entire effect of an adjustment like a dark sheet of paper. In any mask there can be any range of values from 0 (black) to 255 (white). In many masks, we are creating the mask manually, either through a selection or some other controlling method such as a gradient. Masks provide us selective control over how an adjustment is delivered.
The Luminosity Mask
A luminosity mask is simply a mask created to mask out certain levels of luminosity and to pass others through at some level of effectiveness. Simply put, a luminosity mask divides the selection into two halves and passes one half and blocks the other. This is an oversimplification but does illustrate what is happening.
Since we already have five tonal ranges capable of being manipulated in Camera RAW or Lightroom, we are likely to go to Luminosity Masks only when those tools are not sufficient to achieve the creative goals. In this article, I provide instruction on creating twelve new channels that can be used independently to create luminosity masks for an adjustment layer. Since luminosity deals with a brightness value from 0 to 255, they are most effective with those adjustment layers that manage brightness, specifically Brightness/Contrast, Levels, Curves and Exposure. I am using Photoshop CC 2015.5.0 for this article, so some minor elements may differ if you are on a different version.
To begin our work we will go to the Channels Palette. If you do not see Channels as an option in your workspace, go to the Window menu and click Channels to open it. For any image that is in colour, or any black and white image stored as colour (and in reality, all should be) you will see four channels by default. RGB is the composite channel for the three primary colours of light. You will also see individual channels for each colour, Red, Green and Blue. What we are going to do in the following steps is to create twelve different luminosity channels, four for lights, four for darks and four for midtones. It is unlikely that you will need more channels, but the process works for however many you choose. I will be giving each channel a name and extend my thanks to Tony Kuyper, from whom I learned this technique and from whom these names originate. It may occur that when you are making a channel that you will get a dialog box indicating and insufficient number of pixels are available and that the selection will not be visible. This is not a problem, it is simply telling you information about a given selection. What it really means is that there is very little that will fit the channel and therefore nothing of substantive value to use as a mask, essentially resulting in a channel and mask that are completely black, meaning no adjustment will be passed.
We will start by making the first of the Light channels, where Light refers to the areas of the image brighter than 50% grey.
Open the image in Photoshop
Go to the Channels Palette
At the bottom of the Channels Palette is a small circular icon. When you mouse over it, you will see that it is the Load Selection function. Click on the RGB channel thumbnail and drag it to the Load Selection icon and release it
You will know (likely) see a selection of the image indicated by the Photoshop "marching ants". Go to the Select menu and click Save Selection. Name this selection Lights
There are a couple of methods to make the remaining Lights channels. Some involve dragging again but in this article I will document the keyboard method because it is a bit quicker, and because making all these channels gets tedious. The keys you will use are different for Windows and for Macintosh. For a Windows machine, you will use the Shift-Alt-Ctrl combination with your clicks, for a Macintosh machine you will use Shift-Opt-Cmd. Hold all the keys down when you click. In the instructions below substitute your keyboard command for your machine for the word KEY.
KEY click on the Lights Channel
From the Select menu Save Selection as Light Lights
KEY click on the Light Lights Channel
From the Select menu Save Selection as Bright Lights
KEY click on the Even Lighter Lights Channel
From the Select menu Save Selection as Super Lights
You now have four new channels created. There is no eyeball beside any of them, and if there is, click to turn the channel off, or your image looks wonky. Our next step is to make the Darks channels. We use our first Lights channel to make our first Darks channel because Darks are the inverse of Lights.
Click the thumbnail for the Lights Channel. Be sure not to click the eyeball icon
From the Select menu, choose Load Selection and from the dropdown choose Lights. It should be the default.
On Windows hold down Shift and Ctrl and tap the letter I. On Macintosh hold down Shift and Cmd tap the letter I. This inverts the selection
From the Select menu click Save Selectionand name this selection Darks
You have now created your first Darks channel. Now we create three more. The keys you will use are different for Windows and for Macintosh. For a Windows machine, you will use the Shift-Alt-Ctrl combination with your clicks, for a Macintosh machine you will use Shift-Opt-Cmd. Hold all the keys down when you click. In the instructions below substitute your keyboard command for your machine for the word KEY.
KEY click on the Darks Channel
From the Select menu Save Selection as Dark Darks
KEY click on the Dark Darks Channel
From the Select menu Save Selection as Shadow Darks
KEY click on the Shadow Darks Channel
From the Select menu Save Selection as Super Darks
At this point, you now have eight channels in addition to the defaults, four for Lights and four for Darks. Many people stop here but we are going to make four more channels specifically for the midtones. Making the midtones channels is more work as it involves subtracting channels from the base RGB channel to create the midtones channels. If you are on Windows you will use the Ctrl and Alt keys along with the click, on Macintosh you will use the Opt and Cmd keys.
Click the thumbnail for the RGB Channel
On Windows hold Ctrl and tap the letter A, on Macintosh hold Cmd and tap the letter A to select all. You will see marching ants around the frame of the image
On Windows hold Alt and Ctrl, on Macintosh hold Opt and Cmd then Click the thumbnails of the Lights channel and the Darks channel. This subtracts the selections made by the Lights and Darks channels from the image
From the Select menu click Save Selection, and save the selection as Basic Midtones
You have now created the basic midtones channel. It can often happen that you will get the dialog box I mentioned earlier when creating this selection. It just is telling you that there are very few pixels that are perfectly 50% grey. Now let's create the remaining three midtones channels.
Click the thumbnail for the RGB Channel
On Windows hold Ctrl and tap the letter A, on Macintosh hold Cmd and tap the letter A to select all. You will see marching ants around the frame of the image
On Windows hold Alt and Ctrl, on Macintosh hold Opt and Cmd then Click the thumbnails of the Light Lights channel and the Dark Darks channel
From the Select menu click Save Selection, and save the selection as Extended Midtones
Click the thumbnail for the RGB Channel
On Windows hold Ctrl and tap the letter A, on Macintosh hold Cmd and tap the letter A to select all. You will see marching ants around the frame of the image
On Windows hold Alt and Ctrl, on Macintosh hold Opt and Cmd then Click the thumbnails of the Bright Lights channel and the Shadow Darks channel
From the Select menu click Save Selection, and save the selection as Wide Midtones
Click the thumbnail for the RGB Channel
On Windows hold Ctrl and tap the letter A, on Macintosh hold Cmd and tap the letter A to select all. You will see marching ants around the frame of the image
On Windows hold Alt and Ctrl, on Macintosh hold Opt and Cmd then Click the thumbnails of the Super Lights channel and the Super Darks channel
From the Select menu click Save Selection, and save the selection as Super Midtones
Well done! You have now created twelve unique luminosity channels. Take a close look at the thumbnail for each channel. You will see a range of tones from black to white in each channel, this range of tones will now be used to make a mask for an adjustment layer. As a starting point, consider your image and think about what luminosity values you would like to make adjustments to. Then on Windows hold down Ctrl and click the channel thumbnail or on Macintosh hold down Cmd and click the channel thumbnail. This loads the selection made by that channel. Switch to your Layers palette and create and adjustment layer by clicking the icon at the bottom of the palette that looks like a half white half black circle. A menu will pop up. Let's make a Curves adjustment layer so select Curves.
The adjustment layer is created. It will automatically have a mask created with it based on the channel that you selected. The histogram that appears in the Curves callout will show you the values that are being passed by the mask. You can now manipulate the curve and adjust the white and black points by dragging them. There is no "right" answer, this is artist's choice but you will see the effect of your changes in real time on the image. Once you have settings you like, you can close the Curves callout and decide on the next area you want to adjust. Follow the same steps to load the selection from the appropriate channel, come back to Layers and make a new adjustment layer.
This is very much experimentation, because every image is different. Try different adjustment layer types, even those outside the four luminosity adjustments. There is no harm in trying something. If it doesn't work out, just throw that layer away, you will not be damaging the original as Adjustment Layers are non-destructive.
You've now learned how to create Luminosity Channels and to make Luminosity Masks from them and to use those masks with adjustment layers. As the birds say, it's time for you to fly on your own. If you have questions, you can post a comment, or email me directly at ross@thephotovideoguy.ca
Now if you found the method to create all those channels useful but a bit tedious, you can download my FREE Photoshop Luminosity Channel Creation Action right HERE. Simply download the action and double click the file you download to install the action into the action palette in Photoshop. Then when you want to make Luminosity Channels, just open the Actions palette from the Window menu and scroll down to the one titled RC Luminosity Masks. Select it and from the button bar at the bottom of the palette, click the icon that looks like a PLAY button from a VCR or old tape recorder. This will run the action and create the luminosity channels automatically for the current image. You can then use them to make masks with adjustment layers as you wish.
Enjoy and go have some fun! Until next time, peace.