Luminocity Masks in Photoshop

[hanover]

Luminosity masks are very cool, kind of arcane and so useful that I thought I would share them by way of a tutorial. By arcane, I mean a relatively unexplored technique... I have done a lot of photoshop training and very few books or video training packages really delve much into the realm of luminosity masking, yet the technique is so darn useful.

As far as I'm aware, all CS versions will do luminosity masking with the same commands and default hot keys. I'm using CS4 here. In writing this I'm assuming the reader has a basic knowledge of Photoshop, Tolstoy I'm not.

First off, an explanation of the whats and whys.

A Luminosity mask (LM from here on out) is nothing more than a selection based solely on the graduations of the brightness values of the image. In conjunction with Curves Adjustments, these masks provide a very convenient way to select specific brightness values in an image, which can then be altered as you see fit. You would use LM to lighten or darken only very specific areas of the image, like Curves Adjustments on steroids. It begins with a base mask will then be used to make a series of masks for lights and darks using the photoshop functions of intersection and subtraction.

There is a good bit of hot key use creating these masks so you definitely want to record this as an action.

First, create the base mask. I'll call it "Lights".

1. Go to your Channels palette. If you don't see a Channels palette on the anywhere on your interface, go to Window->Channels in the Top menu bar and select it.

2. Drag the RGB channel to the Load Selection button at the bottom of the Channels palette like this:






3. You'll see the marching ants appear on the image. The marching ants are enclosing the lighter areas of the image, looking something like this:







4. Click the Save Selection button at the bottom of the Channels palette. A channel called "Alpha 1" will appear. Double click on the name "Alpha 1" and type "Lights" and then hit the ENTER key to rename this channel.





5. Click on the RGB Channel to make it active, then type Ctrl+D to turn off the marching ants.

And that's it for creating the base luminosity mask for the light areas of the image.

Technically, this is creating an alpha channel. It won't be a mask until it's applied to a layer. That will be covered in the next installment.

[hanover]

Part Two!

To recap part one, we created an alpha channel named "lights" and we're ready for the next steps to make the masks.

1. First, and this is very important, make sure the alpha channel 'lights" is loaded as a selection. Drag the channel to the Load Selection button at the bottom of the Channels palette. It looks like this:




2. Once you see the marching ants on your image, go to the Layers palette. I dragged it here to see it better. At the bottom of the layers palette is a half white/half black circle - the "Create new adjustment layer" button. Click it and select "Curves".





As you see here below, the new Curves layer will appear on the Layers palette with a mask in place that exactly matches the "lights" alpha channel, because it was the active selection.

3. Go to the curves dialog and darken the highlights, like this:





There is no rule on how far down to take the highlights, it depends on the image but a little goes a long way. Remember with masks, white reveals and black hides, so this curves adjustment will affect the more luminous parts of the image more and the less luminous parts of the image less, because of the mask.

In the next installment, we'll use this base mask with intersection and subtraction to make and stack additional curves and mask combinations that are even more fine-tuned to luminance values.

[hanover]

Part Three.

Recapping the earlier installments, we created a luminance mask and applied it to a curves adjustment.

If you're familiar with using curves and masks to bring down highlights and bring up shadows, you're probably already seeing the value here. Essentially, instead of using the selection tools like the lasso tool and painting on a mask directly or using a gradient, we're using the luminance mask to make the selection for us. The benefit of using the LM instead of the selection tools is having a far better degree of, call it self-feathering, with no effort at all and no edges to touch up.

OK. Now it's going to get a little complicated.

We're going to create three more masks that progressively target the bright areas of the image, using intersecting selections of the same mask.

It's done this way:

1. Control+Click the "lights" mask. This loads the mask as a selection and you'll see marching ants in the image.





2. Shift-Alt-Control+click on the "lights" mask. This makes the mask intersect with itself and you'll see the pattern of marching ants change selection to lighter areas.

3. Create a new Curves Adjustment layer. This layer will automatically create it's own Luminosity Mask based on the intersected mask operation in step two. Name this layer "light-lights".

4. Do Step 1 above, this time, on the "light-lights" mask.

5. Do Step 2 above on the "light-lights" mask.

6. Do Step 3 and name this layer "bright-lights".

4. Do Step 1 above, this time, on the "bright-lights" mask.

5. Do Step 2 above on the "bright-lights" mask.

6. Do Step 3 and name this layer "super-lights".

and that's it. What you should have at this point looks like this:





Notice the masks, going vertically up the stack, are progressively darkened. If they aren't, you missed a step or a keystroke - delete the layers and start over until they are progressively darkened.

Remember on masks, white reveals and black hides. Because of the luminosity mask, a Curves Adjustment on the "superlights" layer will feather itself in the image without any harsh transitions. Having multiple masks gives you the control of the adjustment by varying the degrees of the affected light tones.

To get the best effect from all this we really need a set of masks for the Light tones and a set of masks for the Dark tones also. Making a set for Dark tones is the same process only using the Invert command. I'll show that in the next installment.

[hanover]

Part Four.

Recapping the earlier installments, we created a luminance mask named "lights", applied it to a curves adjustment and created three more curves adjustments + luminosity masks progressively darker.

Now we'll simply create a "dark" luminance mask by inverting the "light" luminance mask.

1. Hit Control+D to deselect anything that might still be selected.

2. Control+Click the "lights" mask to load it as a selection, making sure you see marching ants in the image.

3. Shift-Control+I on the "lights" mask to Invert it.

4. Create a new Curves Adjustment. Name this one "darks".

5. Follow the steps the same way the "lights" masks were created, only name these new layers "dark dark", "shadow darks" and "super darks".

When you finish, your layers palette should look something like this:



and there you go.

Adjustments in the "Dark Darks" and "Shadow Darks" will often work best for isolating adjustments to the dark values in the image.

Pretty easy!

So far, we got the light tones and dark tones isolated. Now we need to get the mid-tones and that will be in the next installment.

[hanover]

Part Five (and final)

Recapping the earlier installments, we created a luminance mask to isolate eight levels of luminosity, from very dark to very light. Now we need to isolate the mid-tones.

You may see a warning box pop up on you saying "Warning: No pixels are more than 50% selected". Just hit OK and disregard it. The pixels are still selected, you just won't see any marching ants.

1. Hit Control+D to deselect anything that might still be selected.

2. Hit Control+A to select the entire image.

3. Hit Alt-Ctrl+click on the "lights" mask.

4. Hit Alt-Ctrl+click on the "darks" mask.

5. Create a new Curves Adjustment and name it "Basic Mid-Tones".

6. Repeat Step 2.

7. Hit Alt-Ctrl+click on the "light light" mask and the "dark dark" mask.

8. Create a new Curves Adjustment and name it "expanded midtones".

9. Repeat Step 2.

10. Hit Alt-Ctrl+click on the "bright light" mask and the "shadow darks" mask.

11. Create a new Curves Adjustment and name it "wide midtones".

12. Repeat Step 2.

13. Hit Alt-Ctrl+click on the "superlight" mask and the "superdark" mask.

14. Create a new Curves Adjustment and name it "super midtones".

and there you have it. Your Layers palette should look something like this:





and that's all there is to luminosity masks, just need to group them properly now and unclutter the palette.

As you can see, this really lends itself to creating an action. I run the action on every image that I plan on spending any time with.

You could use a Levels Adjustment layer instead of Curves if you wanted to. You could use them as masks on pixel-containing layers for an HDR-like effect. Actually, the variations are infinite - Hue/Saturation, Photo Filter, Smart Filters, any type of layer that supports a mask.

[docjeff]

Great tutorial Hanover! I'm going to give this a shot later today. Love learning new techniques!