Self Intersecting Luminosity Masks

Posted by ciaran on October 15, 2011 in Blog, Editing & Workflow | 5 comments

A bit of a mouthful, I know Masks are an incredibly powerful feature in Photoshop, which allow you target an adjustment or an effect to a specific area in a photograph, or indeed on the flip side, to control parts of the image where that effect won’t be applied. Well luminosity masks are a similar idea, but rather than choosing a specific area in an image, you can target a specific tonal range, which gives you incredible control over how you can control the tones in an image, particularly useful in monochrome work.

First off, whilst I’ve always been aware of this functionality in Photoshop, I never knew it had a specific name (i.e. luminosity masks) and more importantly, I never knew how to build on the basic functionality, to allow me target more specific tonal ranges. It wasn’t until I read Tony Kuyper’s article on Luminosity masks, that I grasped the full understanding on how to make the selections and realise just how powerful this functionality was. So a big shout out to him!

To be honest, there’s not a lot of point me revisiting all of the content that he has in his blog (coupled with some very useful snapshots), so instead I thought I’d cover the basic hotkeys (PC)

Midtone through to highlight

The first selection is the easy one, and this selects all the midtones through to highlights. It is a feathered selection, so there are some darker midtones included. You camake this selection by:

Clicking on the “Channels Tab”

Ctrl+Click on the RGB Channel

Whilst you don’t have to do this, I’d advise saving the selection “Selection -> Save Selection” for use later. (Call it L01)

Self Intersecting Mask

This is where the “real power” is, in that we can take our previous selection and again divide it in two, choosing the brightest half of the previous selection.

Clicking on the “Channels Tab”

Alt+Ctrl+Shift+Click on the previously saved selection

Again this is a feathered selection, so there is some overlap in tonal range between the tones selected and discarded. Make sure to save your selection again. (L02)

Intersect Again

We can continue to intersect the previously selected tonal range, using the exact same step as before.

Ctrl+Alt+Shift+Click on previous saved selection

Again make sure you save your selection (L03)

One Final Time For the Highlights

You can continue to intersect your previous selection, all the time refining your selection to choose the brightest of the highlight detail. I have found 4~5 intersections is probably as much refining as is necessary. Save this selection and call it L04

At this stage now, L04 really only targets the brightest of the highlight detail and can be used as a mask/selection for any adjustments to this range. Similarly L01 (midtone to highlight) would be a far blunter instrument used for much wider adjustments.

Shadows Through To Midtones

Similar to the midtone through to highlight, we have the exact opposite selection, where we can choose shadow through to midtone. Remember, these are feathered selections, so there is some overlap between both.

Ctrl+Click on either RGB or the saved selection L01

Ctrl+Shift+i (inverts my selection)

Save the selection (Call it D01)

Intersect The Shadows

In the exact same we intersected our highlight selections, we do the same for our shadows.

Ctrl+Alt+Shift+Click on previously saved shadow selection

This now selects the darker half of the tones from the previous selection. Again save your selection (D02)

Intersect Again

And we carry on intersecting as we did with the shadow detail.

Ctrl+Shift+Alt+Click

Each time, we are intersecting our previous selection, selecting only the darker tones.

Save selection (D03)

And Again

As with the highlight detail, the intersections can continue on ad infinitum, but realistically, 3~4 intersections give you a pretty usable range of tonal selections, where anything beyond that is pretty much overkill. So one final selection for our shadows

Ctrl+Alt+Shift+Click

Save Selection (D04)

Targeting The Midtones Only

Assuming you have been saving the selections, a really neat feature is where we can subtract a selection from another, which allows us target midtones only (i.e. no shadows and/or no highlight detail.

Ctrl+A (selects everything – the whole tonal range)

Alt+Click on D04 (removes a small range of shadow detail)

Alt+Click on L04 (removes a small range of highlight detail)

Leaves you with a selection with no pure shadow or highlights

Narrowing In Even More

The Alt+Click subtracts one selection from another, so you can continue to just Alt+Click on the narrowest highlight (L04) and shadow (D04) detail or go quickly in on the midtones by using larger selections like D02 and L02

This allows you narrow in even more specifically on the midtones, giving you a really useful mask for specific adjustments.

The whole nature of this process means it can be automated using Photoshop Actions and of course thats exactly what I did (my actions are free to download). At the click of a button, my image is partitioned into different selections for the different tonal regions in a shot.

BE CAREFUL If you so save your selections and you save your image as a layered image (TIFF or PSD) then the selections can add a lot of disc space to your image. I also have an action to remove the luniosity masks, which I do before saving.

These masks allowed me to tone the image above of Raphaella, starting off with a reasonably flat conversion and moving towards a quite punchy B&W.

The Video