Luminance Masking allows you to control the contrast of your image in specific tonal ranges. In this article you will learn how to use the included set of Actions to make a quantum improvement in the contrast of your images.

These masks will intensify the detail and tonality of your images and add snap and sparkle that is not possible without using either this technique or one of a number of plug-ins that do this under the hood. One big difference is that this process is free.

If you are ready for some intermediate to advanced photoshop discussion continue onwards, read the article, download and use the actions and get excited like I did when I started using this process in 2007…

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Once the photograph has been taken, and HDR composited if necessary, and is ready to be adjusted. This is where you can apply your tonal post-visualization of the scene to the digital original.

Because your eye is a much more perfect imaging device then the camera often photographs do not appear as you saw, or imagined you saw, them at the time of capture.

To make these after the fact contrast adjustments you can use Luminance Masks. I have created a set of actions for Photoshop that will allow you to rapidly produce the masks for your image. The generation of the mask action is beyond the scope of this discussion, as you want to learn to use the masks rather then make mask action sets. If you are generating the masks for a large image be patient as it will take a few minutes depending on your station.

A luminance mask is essentially a band pass filter that passes a range of tones while excluding tones that are not included in the band. As with any band pass filter there is a degree of interaction outside of the band as the roll off (or rejection) of values outside of the selected range is not absolute.

You can create any number of masks for your image but it is easiest to think about using them as two or three band contrast equalizers. Once a the basic contrast ranges in an image have been equalized it is easy to add more specific regionally limited masks to your image.

A two band equalizer has two levels layers. One is a LPF, lo pass filter, and a HPF, high pass filter. The two bands allow you to alter the shadows or the highlights independantly.

A three band equalizer adds a mid-range filter to provide for Low, Middle and High levels layers. Usually you will see the effects of the band pass filter in the levels layer’s histograms. I commonly use 0-III for low, V for middle and VII for high.

The mask is a continuous tone B&W representation of your image. If you plan on doing major retouching do it before you start the masking process. If you wait until the luminance masks are added you will have to flatten the image and then do the retouching. You will need to flatten your image for sharpening as the image is contained in the masks as well as the background pixel layer.

To name the masks I made a series of exposures of a test target placed on each of the zones with my Nikon D200 and Canon D5 Mk II. The tone curve/rendition was set to normal.  I cut those frames up and made gray scales from the swatches. I then made a set of luminance masks of the gray scale and by loading each selection I named the mask by the zones that were primarily selected. The masks will select tones outside of those that are named but will affect them to a lesser extent. The illustrations below show the roll off characteristics of each mask.

Zone 0-IX from 2 Cameras

I made a set of masks using the ramp and scales from the above file. I loaded each selection and set it as the transparency mask on a solid color layer. This clearly illustrates the range of tones selected by each mask. You can see the roll off characteristic in the filters by the steps that are not 100% selected.

Zone O-III enables you to both lighten your shadow values and add contrast to them. I use the 0-III mask frequently as it has good rejection in the high values and gives solid coverage in the low range.

Using 0-V or O-IV and VI-IX layers provides a nice 2 band solution.

Zone V covers the midtone areas with a band pass that is centered on zone 5.  I use the Zone V mask all the time as it lets me tune up the midtone values without too much effect in the highlights and shadows. I like using a three band process.

Zone V-VII is a smooth mid tone mask that can add detail and punch to the high mid-tones.

Use this or Zone VII-IX with 0-V for a nice two band contrast adjustment.

Zone VII-IX is good for building up the detail and contrast in your highlights.

I use the Zone VII mask all the time to add some detail and punch to my highlights. Cranking up the low on this will add detail to a flat detail-less highlight and pumping up the high will create sparkle.

Zone VIII-IX can give detail to flat light highlights.

This mask is good for tuning the highest highlights.

Step by Step Use of the Masking Action Set

If the image is not full range, 30-245ish, Running action 2a or 2b to build masks will generate recoverable errors.

• Run the Generate Masks action
  • Two actions are supplied to generate masks for LAB and RGB color modes.
  • If you make the histogram window visible during execution you will see the bands being generated.
  • When the action has completed execution look in the Channels window and you will find the masks that were generated.
  • If any errors occur hit Ok or Continue until the action is complete. If this happens you might consider re-doing step 3 - Normalize Density.

• Apply masks using Make and Intersect Actions.
  • Select the layers pane and click on a visible layer so that it is highlighted in blue. If a visible layer is not selected in blue an error “Make Command Not Available”. If you get this error select a visible layer and run the generation action again.
  • Equalizer Presets
    • Two Band and Three Band Presets are included in the Action set.
      • 0-III/V-VII Two Band
      • 0-III/V/VII Three Band
    • Overall contrast masks  - Make… type Actions
      • Run the Make action for the range of zones you want to effect. This will build a levels adjustment layer with the luminance mask in the alpha channel of the layer.
      • Adjust the levels to suit you purposes. On masks that do not include the high zones it is possible to use strong high and gamma settings without burning highlights. On masks that do include the high zones strong low and gamma corrections can be used.
    • Regionalized masks – Intersect… type Actions
      • Create a feathered selection of the area to change in your image.
      • Run the Intersect action for the appropriate zone range.
      • This will make an intersection of your feathered regional selection and the luminance mask.
      • This produces hard to detect mask edges as well as the ability to control the contrast and detail on selected areas.

• Dealing with color over-saturation.
  • Often after an RGB image has been masked to have snappy contrast it will become over saturated with color. To correct this saturation problem put a Hue/Saturation adjustment layer on top of the stack in the Layers window and set the master channel’s saturation to between -5 and -15. LAB images do not suffer from this problem. I find the results of this process are better with LAB images but I frequently work in RGB because I like the adjustment layer selection better.

• Clean up…
  • When you are done applying the luminance masks you MUST RUN THE CLEAN UP ACTION!!!.
  • This will remove the unnecessary channels holding the stock of luminance masks.
  • If you do not run Clean Up then image will SAVE VERY SLOWLY and it will CREATE A HUGE FILE.

  Remember to run Clean Up every time…
  

  How I Use Luminance Masks

  I use these masks to enhance the contrast of my images. By loading a mask into the transparency layer of a levels or curves adjustment layer you can control the contrast of a limited tonal range of your image. You can also perform shadow noise reduction through the low pass filters. I will often add one of these filters to an over or underexposed frame to create a 16 bit HDR effect that is undetectable. I can usually tell a 32->16 bit HDR image from across the room and that kind of tonal distortion is rarely my goal.

  Before generating masks for your image observe the density targeting to be sure your image has high values in the 145-150 range. To simplify this process there is a action called Make Targeting Layers. Run it and adjust the hi slider of the overall levels control until some white spots appear in the black of the threshold layer. Turn off the threshold and visually evaluate the effect to be sure you have not gone too far.

  Run the Generate RGB or Generate LAB Masks action as appropriate for your color mode. If you do not have a full range image the Generate Masks action will pop some errors. If this happens hit Ok and Continue to get through the error and the action will build as many masks as is possible.

  I prefer using the levels layer for general contrast adjustment so I made a set of Make and Intersect actions to make it easier for intermediate workers. One cravat is that you must have a visible layer actively (blue) selected in the Layers pane or these actions will complain “Make Command Not Available” and fail. If this happens click on a visible layer in the Layers pane until it is blue, actively selected.

  Make actions create a levels layer with the named mask in its transparency layer and set the name appropriately.

  Intersect actions expect an active selection somewhere in the image. They load the selection in intersect mode so that the mask is confined to the area that was selected and add this selection to a named levels layer. This allows you to contrast control specific areas. When making the initial selection select a feather value that will create a soft edge.

  Luminance masks tend to create soft edges but you must never blur a luminance mask as it will soften the focus of that area, remember it contains a B&W representation of your image.

  I use the actions to create a basic set of overall adjustments for my image. Commonly I will make Zones 0-III, V, VII and then make my later intersect type selections from those masks. This saves paging into the channels pane. I like to make intersect selections manually as it allows me to see the marching ants. The ants give me some indication that I am selecting the value I am trying to target.

  To make an intersect selection press the three modifier keys, Mac-Cmd-Opt-Shift/PC Ctrl-Alt-Shift, and then click on the mask that you want to intersect with your currently active regional selection. The intersected mask will contain only those areas selected in both selections. To manually load masks flip over to the channel pane and you will see them below your RGB or LAB layers. With an active regional selection intersect click on a channel thumbnail. Look at the way the ants march in your region. Hit undo to return to the region and repeat the process with several other masks. By watching the ants march you can determine how your regions values are being selected. You will not see the ants in you use the Intersect actions.

  On the overall adjustments I am moving the low and high sliders of the levels control towards the ends of the mountain and moving the gamma slider to lighten or darken as necessary. This is a very “season to taste” sort of process so you just have to experiment. You can make much more radical adjustments to the sliders that you can without the mask in place.

  Once I have made the over all adjustments I will make a regional selection of the areas where I want to burn, dodge or accentuate using a lasso or whatever, feather the selection, then intersect that selection with a luminance mask of the tone range I want to adjust.

  Enhancing localized areas with regional luminance masks will expose a great deal of detail in your image that was not visible prior to masking. Your overall contrast will be markedly improved.

  When you work in RGB your colors will become more saturated which is not always bad. If it is too much apply a Hue/Sat layer on top of the adjustment layer stack and set the master Saturation somewhere in the range of -5 to -10ish.

  By working in LAB color your colors will not be affected by the masking process but your will have less of the adjustment layer types available to you. If I intend to really pound on the contrast in a given image I will work with it in LAB mode.

  When you are done with a masking session you simply MUST run the Clean Up action. If you do not do run this action your file will be huge due to all the extra channels. I work on large images and find that I like to run clean up ASAP as it can affect my performance with a 100mp image and I can continue to select from my overall masks that are retained in levels layers. When I am done masking I will flatten the image for sharpening and a final round of spotting and sharpening.

  If you were to take an image and process it by your normal methods and then process the same image using the luminance masks the difference will be most clear. When I learned this and developed the initial action set it was a real “everything I know is wrong and everything will need to be redone” sort of a moment. Hopefully I can share that feeling with you through this wonderful channel chop!

  The luminance masking action set and this white paper are available for free via the link below.

  Download the Luminance Masking Action Set and White Paper

  Please do not redistribute these assets via other web sites, if you want to share it online use a link to the article page. Feel free to pass the URL on to your fellow photographers.

  Have fun!

  Cooksey