Blending Mode Slayer Tech

92

ct Digital Photography 10 (2013)

Copyright by Heise Zeitschriften Verlag

Michael Jordan

Developing Imagesusing Blending Modes and Layer Techniques

93

Photographers have a lot to gain from advancedblending mode and layer techniques that go beyondsimply selecting Overlay mode and playing around withopacity values. These techniques offer exciting newimage editing options using just a few mouse clicks.

This article not only tells you whatPhotoshops layer techniques andblending modes are called and where to findthem, it also explains how to combine themwith photographic know-how to producefantastic image editing results. There arehands-on examples that show you how toselectively improve the tones in your colorand black-and-white images, and youll alsofind tips on how to produce HDR images whileretaining complete control of the quality andlook of the results. We explain how to adjusttonal values separately for highlight andshadow areas and present subtle but effectiveways of sharpening your images. And if allthat isnt enough, we also let you in on thesecrets of Lab mode and how to use it withblending modes to provide virtually endlesscreative image editing options. To help youpractice, we have included the sample imagesused in the tutorials on this issues free DVD.


Blending Modes for Photographers | Introduction


If you usually stick to standard tools such asLevels, Curves and Color Balance, you maywell be asking yourself what Blending Modesare. However, if you are familiar with theLayers panel and its associated tools, you willprobably have used blending modes (alsoreferred to as layer modes) quite a lot.

You will often come across blendingmodes if you use the Photoshop Apply Imageand Calculations commands. Blending modesare also an integral part of the Paintbrush,History Brush and Gradient drawing tools, aswell as the Healing Brush, Clone Stamp, Blurand Dodge retouching tools.

Photoshop CS6 includes a list of 27 differentblending modes, divided into six groups.

The first group consists of the Normal andDissolve modes, which have no obviouseffect. The modes in the second group darkenan image and those in the third are used toperform general image lightening. The fourthgroup makes dark tonal values even darkerwhile brightening lighter ones, and the fifthgroup creates a mathematical relationshipbetween the two basic tonal areas. The sixthand final group combines tonal values,saturation, color and luminosity in a variety ofways.

Generally speaking, blending modes areused to merge various types of image data. Inorder to perform this task successfully, all thedata that you wish to merge has to have thesame basic proportions so that the individualpositions in the images being merged areprecisely mapped to one another. If youimagine two overhead projectortransparencies laid on top of each other, eachpoint on the top transparency correspondsprecisely to the one underneath it, which isexactly how blending modes merge pointswithin separate images. In other words, thefirst pixel on the first row is merged with thecorresponding pixel on the layer beneath andso on, through to the final pixel in the bottomrow of image data.

This way, images, layers and channels ofthe same size can be merged either with eachother or with duplicates of themselves.Eight-bit RGB images are saved in the form ofseparate red, green and blue channels, eachof which contains a maximum of 256 differenttonal values (between 0 and 255). If these

tonal values are multiplied (i.e., 256 x 256 x256), the result is the well-known total of 16.7million different colors that an 8-bit image cancontain a gamut that provides a huge rangeof nuances. If you imagine each of these colorsas a one-millimeter strip, the ribbon theywould form would be 16.7 kilometers (about10 miles) long. Imagine merging two ofthese ribbons, and it quickly becomes clearwhy it can be quite tricky to keep track ofwhats going on when applying blendingmodes.

To begin with, it is sufficient to note thatblending modes can be used to merge imagedata from images, layers or channels that arethe same size. The results either show nochanges (in which case you can do withoutblending altogether) or are brighter or darkerthan the original image. Things get reallyinteresting when the darker areas of theresulting image are darker than the originalbut the brighter parts are lighter.

So now you know that there are 27different blending modes that can be used tomerge various types of paired image data.One of the two elements is the source and theother is the target. An active element isautomatically considered to be the target, soif you are working with two superimposedlayers, the blending mode you select will beapplied to the upper of the two layers.

To select a blending mode, simply click itin the blending mode list (on a Mac, you canuse the Shift-Alt-Initial shortcut, where Initialrepresents the initial letter of the modesname). The Darker Color, Lighter Color,

94 ct Digital Photography 10 (2013)

Blending Modes for Photographers | Overview


What Are Blending Modes?

The list of Blending Modes found inthe Layers panel or the LayerOptions menu

y11

x12

x13

y21

y12

y23

x11

x12

x13

x21

x22

x21

R11

255

x11

255

y11

255=

x11

= 154

y11

= 154

R11

= (0.60 0.60) 255

R11

= 0.36 255

R11

= 93

R11

=154255

154255

255

E1 (Multiply) Sample merge

Background layer

This is how blending modes work. In this case, Multiply mode transforms the two 154tonal values (x11, y11) into a value of 93 (R11) when merged.

Subtract and Divide modes are not associatedwith a default shortcut, but you can add yourown using the Edit > Keyboard Shortcutscommand.

Photographic Image Editing

If you grew up in analog times, you will knowthat shooting and enlarging ablack-and-white image really meanscapturing and reproducing the best possiblerange of grayscale tones. The tonal range ofthe film or sensor in a camera often vastlyexceeds that which can be reproduced onpaper. In other words, a printed image isalways a tonal compromise. In the heyday ofblack-and-white analog photography, manypeople aspired to perfect tone management,and Ansel Adams famous zone system was apioneering attempt to optimize therelationships between the tones produced bythe image capture, negative developmentand print enlargement processes.

Digital images, too, basically consist ofgrayscale values that range from pure blackto white on a scale from 0 to 255 for each ofthe RGB channels. It is theoretically possibleto adapt Adams zone system with its

95ct Digital Photography 10 (2013)

A typical landscape photo. The histogram displays tonal values coveringthe entire scale from 0 to 255. The individual channel views shown on page 96 provide a more detailed breakdown of their distribution.


The Layer Style dialog offers more options for fine-tuning the application of blending modes. The Blend if options enable you to precisely adjust the overall effect of a blend and thetransitions it creates.

values from 0 to X to the world of digitalimages; although the original system wasdesigned to create unique combinations ofexposure and development parameters thatonly ever applied to a single image. Thebasic idea of influencing the various areasof brightness within the frame individually isjust as valid for digital images. Blendingmodes are a little-known but very effectivetool for applying just this kind ofphotographic adjustment, and allow you toeffectively isolate and adjust highlights,midtones and shadows. Generally, each ofthese three zones contains about a third ofthe tones in an image, with shadow valuesranging from 0 to 85, midtones from 86 to170 and highlights from 171 to 255. Basedon this assumed distribution, selecting yourdesired pixels is a matter of just a few clicks,rather than the often painstaking workinvolved in using Photoshops variousselection tools. Whats more, you can thenedit each of the three zones completelyindependently (see the workshop on page98).

Preparing Your Image

The first step in the process we are about todescribe involves adjusting the levels in eachcolor channel so that the tones it contains

cover the maximum possible range. Thisensures that the results are as dynamic aspossible, and the results will be just as goodwhether you use the Curves tool or the Levelstool to make the adjustment.

Adjusting Levels

When you open it, the Levels dialog looksmuch like the one shown on page 95. Here,the overall shape of the curve is less importantthan the behavior of its two ends. Your imagewill display maximum contrast (i.e., it willcontain the maximum possible range of tonalvalues) if the curve actually touches both endsof the tonal scale.

In order to achieve maximum imagequality, you will need to adjust each colorchannel individually. The illustrations aboveright show just how different the distributionof tonal values in the channels can be. Movingthe black point and white point input sliderstoward the center of the scale distributes theavailable tonal values across the entire scaleand, if you hold down the Alt key while doingso, the preview will show clipped areas (i.e.,ones that are completely black or completelywhite) in the resulting image. Once the sliderreaches the end of the histogram curve, theassociated pixels will be shown in color in thepreview image.

The adjusted image has a lot more contrastand will look more dynamic. The differencesthis type of adjustment make can be quitedramatic, but your results will always dependon the quality of your source material.


Blending Modes for Photographers | Levels


Once the levels have been adjusted, the resulting image displays maximumcontrast and is much more dynamic than the original

Comparing the individual color channelsshows how important it is to adjust contrastseparately for all three


Blending Modes for Photographers | Highlights, Shadows and Midtones


Prepare your mask: Duplicate thebackground layer twice using the DuplicateLayer command in the Layer menu. Selectthe Color Burn blending mode for theuppermost layer and merge the two upperlayers into one. Use the Select > Allcommand (or the Ctrl/Cmd+A shortcut) and copy the resulting selection using theEdit > Copy command (Ctrl/Cmd+C). Theselection is now stored on the clipboard.Now hide this layer by clicking its eye iconin the Layers panel.

Step1

Mask the shadows and midtones:Duplicate the background layer once againandrename the new layer Highlights.Create a new mask using the Layer > LayerMask > Reveal All command and paste thecontents of the clipboard into it by holdingdown the Alt key and clicking the mask,followed by the Edit > Paste command(Ctrl/Cmd+V). The shadows and midtonesare now masked, and you can delete thehidden layer.

Step 2

Brighten the highlights: Any levelsadjustments you make to the Highlightslayer for example, using the Hard Lightblending mode now only affect the brightimage areas. You can also use Curves toadjust the highlights. The fact that themidtones and shadows are masked givesyou a lot of leeway for your adjustmentsand allows you to experiment with settingsthat would be too extreme for applicationin an unmasked image.

Step 3

Adjusting Highlights, Midtones and Shadows

This workshop demonstrates how to create masks that allow you to adjust highlights,shadows, and midtones separately. This approach enables you to optimize one zoneat a time once you have adjusted the basic color levels in your image.


Blending Modes for Photographers | Highlights, Shadows and Midtones


Adjust the midtones: Because the brightesttones in this mask are mid-gray, adjustments tothe midtones wont have a particularly markedeffect. If you want to produce a more obviouseffect, you can always use the Curves or Levelstools to increase dynamic range. To brightenthe Midtones layer, use either the Curves toolas shown, or an appropriate blending mode.

Step 5

Prepare to adjust the shadows: Once again,duplicate the background layer twice. Thistime, select the Color Dodge blending mode.Once you have merged the two upper layers,copied the result and hidden the new layer,you can duplicate the background layer andcall it Shadows. Create a mask, insert theclipboard contents and invert the mask usingthe Image > Adjustments > Invert command.This creates a shadows mask. Now delete thehidden layer.

Step 6

Adjust the shadows: You can darken theShadows layer using either Multiply blendingmode or the Curves tool.

As you can see, creating zone masks is quickand easy, and is even faster if you use Actionsto create your masks. You can even record asingle Action to create all three masks in oneroutine and simply delete the masks that youdont need for the image you are working on.

Step 7

Prepare to adjust midtones: The methodhere is basically the same as for the highlights.Duplicate the background layer twice andselect Exclusion blending mode. Merge thetwo upper layers into one, select all, copy theresult to the clipboard and hide the new layer.Duplicate the background layer again and callit Midtones. Create a mask and activate it byclicking it with the Alt key pressed. Now pastethe contents of the clipboard into the maskand delete the hidden layer.

Step 4


Blending Modes for Photographers | Tonal Adjustments


You can use the techniques introduced in the workshop on page 98 to fine-tune thethree basic tonal zones in black-and-whiteimages too.

Using the individual RGB channels withinthe Curves or Levels tools gives you evenmore ways to use zone masks to enhance yourimages. Adjusting the individual colorchannels within each zone enables you toapply sophisticated effects like those you can produce using the Lightroom SplitToning tool, which allows you to finelybalance the adjustments you make to theindividual zones.

Subtle adjustments to highlights andshadows can make black-and-white imagesseem more three-dimensional, especially ifthe differences between your tweaked image and a conventional grayscale versionare not immediately obvious. For the portraitof a child shown below, we created andadjusted shadow and highlight masks toachieve the effect we were looking for. In this case, a slight lift in the red channel curve was all that was required to addwarmth to the shadow areas.

Similarly, lowering the blue channel curve for the highlights also warmed up the

brighter areas. The result is very subtle andgives the finished image added charm.

Creating a Look

The possibilities are virtually endless, and you can achieve similar effects to themonochrome ones described here in colorimages using any or all of the color channelsin any combination of the zone masks wehave already created. Green is the dominantcolor in both the light and dark the areas inthe image of an ornamental leek bud shownopposite. Increasing the red component in

Advanced Tonal Adjustments

Subtle adjustments tothe individual colorchannels in the shadowand highlight zones givethis black-and-whiteimage extra impact

Continued on page 104



Using blending modes and the Curvestool, you can produce enhanced color

looks like this one with just a few clicks

Here, we brightened the red channel anddarkened the green and blue channels inthe shadow zone to accentuate the red

tones in the darker image areas


Bildbearbeitung | Fllmethoden fr Fotografen

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Simultaneously reducingthe red component whileincreasing the green andblue levels gives themidtones a cooler look

Highlights react in a similar way to midtones, producing a cold/warm contrast alongside thelight/dark contrast that already exists between the highlight and shadow areas


Blending Modes for Photographers | Tonal Adjustments


Deliberately blurred highlightscan give a photo a filmy, ratherromantic feel

The mask shows precisely which parts of theimage are affected by the added blur

Because the higher Radius setting alsoincludes pixels taken from the yellowleaves, a strong blur effects gives the sun anexaggeratedly yellow tint

the shadows offers an effective counterpointto the green-tinged highlights. To begin with,we adjusted each channel by eye until weachieved a satisfactory look for the darkertones.

We then adjusted the midtones channelby channel, reducing the red componentand increasing the green and blue levels.Adjusting the upper end of a curve morethan the lower end ensures that effect on

the midtone areas is more pronounced.Finally, we applied similar adjustments tothe individual highlight channels, againreducing the red component and increasingthe green and blue levels. You can, of


Blending Modes for Photographers | Sharpening


It doesnt alwaysmake sense tosharpen the entireimage. Subtle partialsharpening in theshadow areas is oftenmore effective, asshown here in thedetail of the tire.

The Shadows mask showswhich parts of the image will

be affected. Using masksallows you to apply muchmore radical effects than

you can when sharpening anunmasked image.

course, adjust the overall brightness for anyor all of the zones using the combined RGBcurve.

Romantic Highlights

Blur effects can also be used to alter the effectof the highlights in an image. Selective bluroften gives portraits and landscapes acharacteristic look of their own.

To apply a selective blur effect, duplicatethe background layer twice and select theColor Burn blending mode for the upper layer.Merge the two upper layers, copy the newlayer to the clipboard and then delete it. Youcan then duplicate the background layeragain, create a new mask and paste thecontents of the clipboard into it.

Now apply the Gaussian Blur filter to theduplicate background layer. The effect youachieve will depend on your Radius setting,

which will itself depend on the size of theimage you are working on. In our backlit forestexample on page 103, you can see the resultsof applying radius settings of 7.2 and 90. Theblur filter darkens the highlights; tocounteract it you will have to apply a Curvesadjustment or use a blending mode such asScreen from the third group in the list.

Subtle Sharpening

The logical counterpoint to blurredhighlights is sharpened shadows. Thebrighter areas in many images tend to lookrather two-dimensional, so the generalimpression of sharpness is determined moreby the sharpness of the shadow details. Toenhance this effect, create a shadow zonemask, copy the background layer twice andselect Color Dodge blending mode for the

uppermost layer. As previously, you thenhave to merge the two upper layers, copy theresulting content to the clipboard and deletethe layer. Then make a new copy of thebackground layer and create a mask that youthen fill with the contents of the clipboard.Invert the new layer using the Image >Adjustments > Invert command. Again, youcan save a lot of time by recording thesesteps in an Action, especially if you useshadow masks regularly.

You can now apply the Unsharp Maskfilter to your new layer. As with the othereffects we have described, you can applymuch more extreme values to a maskedimage than you can use on a conventionalimage layer. Using this approach, you canselectively increase contrast in the darkerareas of your image as we have with ourrace car photo which not only increasessharpness, but also adds depth.



Blending Modes for Photographers | Sharpening


Blending Modes for Photographers | HDR


Create a highlight mask: Open all three source images inPhotoshop and use the normally exposed image as the basis forthe step-by-step creation of HDR shadow and highlight masks.Duplicate the background layer twice and select the Color Burnblending mode for the upper layer. Merge the two upper layersand call the resulting layer Highlight Mask. Now switch to thesource image with the shortest exposure time (i.e., theunderexposed one in which the highlights show maximum detail)and copy it to the clipboard. Switch back to the normally exposedimage and paste the contents of the clipboard onto a new layercalled HDR Highlights. Create a new mask and activate theHighlight Mask layer. Use the Select All command and copy theresulting selection before deleting the Highlight Mask layer. Nowpaste the copied mask into your newly created mask by clickingthe mask with the Alt key pressed, followed by the Ctrl/Cmd+Vshortcut. The resulting image now has good highlight detail, butdoesnt yet look convincing.

Step1

Fine-tune the highlight mask: Payingattention to the transitions between thehighlights and midtones as well as thegeneral feel of the image, reduce the opacityof the highlight mask layer until thehighlights show just the right level ofbrightness and apply the Gaussian Blur filter.Larger Radius values make these transitionssofter. Once you have found the right Radiussetting, you can re-adjust brightness ifnecessary.

Step 2

Creating HDR Effects Using Blending Modes

Another way to use your new knowledge of blendingmodes is to create enhanced-contrast images. All you needis a high-contrast subject that you capture in three separateimages, one using exposure settings that produce a normalimage and two others that capture all the highlight andshadow detail. The normal image should be exposed at alevel that approximately represents the overall brightnessthat you want your finished HDR image to have. Use atripod to ensure that the three images can be perfectlysuperimposed.

Normal exposure Underexposed Overexposed


Blending Modes for Photographers | HDR


Create a shadow mask: Hide the HDRHighlights mask and duplicate the backgroundlayer twice. Select the Color Dodge blendingmode for the upper duplicate, merge the twoupper layers and invert the result using theImage > Adjustments > Invert command. Callthe result Shadow Mask. Now switch to theoverexposed image (i.e., the one with thelongest exposure time and good shadow detail).This means that the brightest source image isresponsible for creating the darkest parts of thefinished image. Select the entire image andcopy it to the clipboard. Now switch back to thenormal image and paste the new contents ofthe clipboard to a new HDR Shadows layer.Create a new mask, activate the Shadow Masklayer, apply the Select All command(Ctrl/Cmd+A), copy the resulting selection anddelete the Shadow Mask layer. Paste the copiedmask into the HDR Shadows layer by clickingthe mask with the Alt key pressed followed bythe Ctrl/Cmd+V shortcut.

Step 3

Fine-tune the Shadow mask: The HDR Shadows layer we havecreated looks OK, but could benefit from a little tweaking using theGaussian Blur filter, though with a much smaller Radius setting than theone we used for the highlight image. Increase the saturation of the HDRShadows layer using the Image > Adjustments > Hue/Saturationcommand to accent the shadow tones. Once you are happy with all yourshadow and highlight settings, you can merge all your layers into onebefore making any final global adjustments to contrast and brightness.This is the point at which you can apply additional sharpening too, ifyou wish.

However you decide to apply these techniques, the masks we havecreated and the uses of blending modes and layers that we haveoutlined are very useful for identifying the highlight and shadow detailsyou want to emphasize and the effects of the adjustments you make tothem.

Step 4

Some users consider the High Pass filter to bea strange and exotic tool, while others find itan indispensable aid to everyday imageediting. The filter thinks somewhat out of thebox but, once you have understood how itworks, there are many ways to apply iteffectively. However, you can only realize itsfull potential if you use it in combination withblending modes. The five tone levels includedin a grayscale wedge illustrate the filtersprinciple very well, as they represent tonalvalues of 0, 64, 128, 192 and 255 in all threeRGB channels (i.e., tonal variations at regularintervals).

The High Pass Filter

The High Pass filter can be found in thePhotoshop Filter menu under Filter > Other.When applying the filter to a grayscale wedge,you can select Radius values between 0.1 and250 pixels, and the effect is only visible atobvious edges (i.e., where there is contrast).Where there is no contrast, the filter producesmid-gray pixels. The filter can be applied to

any layer (including the background),although this doesnt make much sense, asyou will see if you try applying it to a grayscalewedge as an experiment.

An edge is produced where dark and lightimage areas meet, and applying the High Passfilter produces a dark line on the dark side anda bright line on the bright side of the edge.The larger the Radius value you use, thebroader these lines will become, up to thepoint at which they form a visible, mediumgray band. In our example opposite, the dark-to-light transition moves from left toright, which means that the dark bands formon the left and the bright ones on the rightwhen the High Pass filter is applied. A Radiusvalue of 3.0 produces a fine edge line and theremaining tonal bands all turn to mid- gray.

If we apply a much larger Radius value,such as the 90 we used in our example, theedge lines are transformed into broadgradients, making it impossible to tell how theoriginal image might have looked by studyingthe results produced by the filter. If yoursource image doesnt contain any distinct

changes in tone (i.e., edges), applying theHigh Pass filter will produce consistent graytones throughout the frame, irrespective ofthe Radius value you use.

At first glance, the High Pass filter doesnthave any obvious uses in a photographiccontext. The only exceptions are if you use itwith blending modes or to create a mask forisolating edges that you wish to tweakselectively.

In order to apply blending modes, youhave to duplicate the background layer firstand apply the High Pass filter to the copy.

The blending modes from the fourthgroup apply effects similar to that producedby applying an S-curve with the Curves tool i.e., they brighten highlights and darkenshadows and combine well with the HighPass filter. If you merge any tonal value fromone layer with mid-gray from another using ablending mode from the fourth group, theoriginal brightness will remain unchanged inthe parts of the original image where graypixels are located. These blending modes onlyhave an effect in places where non-mid-gray


Blending Modes for Photographers | Advanced Techniques

Advanced Blending Mode Techniques

Photos with well-defined monotone areas, such as the sky in this photo, can benefit from sharpening using the High Pass filter.The filter sharpens only edges, leaving detail in major shapes untouched and preserving overall image data quality.


tonal values are present in the original image.As we have already seen, the High Pass filterproduces distinct lines at object edges, soapplying it here increases edge contrast,which also sharpens the image. Soft Light isthe subtlest mode of the group, while Overlayand Hard Light produce slightly strongereffects. Vivid Light and Linear Light producethe highest-contrast results of all.

The best way to get a feel for the effectsproduced by the High Pass filter is to applyany blending mode from the fourth group toyour duplicate layer and then apply the filter.Doing things in this order makes it easier tosee which Radius value best suits the imageyou are working on, and you can alwaysswitch to a different blending mode once youhave selected the right filter settings.

Combining Tools and BlendingModes

Blending modes can also be applied usingvarious brushes and retouching tools. With alittle practice, this direct style of applicationcan be a lot quicker than using separate layersto apply your chosen effects, especially whenyou are performing minor adjustments. The




We used a grayscalewedge to represent therange of tones within animage. Applying the HighPass filter with a lowRadius value producesdistinct lines at the edgesof the individual zonesand consistently gray colorfields. Higher Radiusvalues produce distinctgradients at every edge.

following example uses the Brush tool toillustrate the principles involved in thisparticular technique.

Use the Brush tool with a low hardnessvalue and a size setting commensurate withthe image you are working on you should beable to perform your intended adjustmentwith a single stroke. Select white as your colorand reduce opacity to between 30 and 60%.In this case, use the Soft Light blending mode;if you are aiming to produce higher-contrastresults, use Overlay (or even Hard Light) . Nowall you have to do is paint in the areas youwish to brighten. If you are not satisfied withthe results, use the Edit > Step Backwardcommand or undo the step in the historypanel to undo your adjustment and startagain.

Using layers to achieve the same effecttakes longer. If this is the approach you wishto take, first create a new layer using the Layer > New command and select anappropriate blending mode and opacitysetting as described above. Select a whitebrush in Normal mode and set opacity to100% with size and hardness settings asdetailed in our previous example. You cannow paint your adjustment into your newlayer. The result is the same as thebrush-based one, but can be adjusted at anytime by adding to or erasing the areas youhave painted.

For completeness sake, we would alsolike to mention a third technique that builds

on the second example we have justdescribed. Instead of creating a blank layer,fill the new layer with 50% gray by using theEdit > Fill command and selecting the 50%gray option in Use drop-down in the Filldialog. This is the same gray that blendingmodes such as Soft Light use. While thisdoesnt actually have any effect on theresults you produce, it does make it a loteasier to see where you have painted in yourediting layer.

If you want to add a vignette effect to animage, you can either use a selection with asoft edge and the Levels tool, your RAWconverters built-in tool (if available) or a large,soft brush. If you want to leave the color ofyour vignette as it is, use a dark neutral graytone or black with reduced opacity. Using acolor picked from the tones included in theimage itself is a great way to emphasize theeffect of a vignette.

We used just a couple of brush strokes andScreen blending mode with a brightyellow/green tone and 42% opacity tobrighten the background in the image of aflower bud opposite. Once again, we couldhave worked with separate layers, but directuse of brushes and blending modes helped usto produce a quick and effective vignetteeffect. This approach also allows you to useany shape you like for your vignette, anadvantage that is lacking if you use a soft-edged selection or your RAW convertersbuilt-in tool.

Lab and Blending Modes

To give you a taste of the real potential ofblending modes, we would also like to take anexcursion into the world of Lab modeadjustments. Lab mode images have threechannels too, but instead of representing thecolors red, green and blue, they are called L, a and b, where L stands for Lightness anda and b represent the color-opponentdimensions described by the Lab color model.Using this model can take some getting usedto (see page 112), especially if you are used tousing RGB channels. However, once you haveunderstood the principle involved, you willquickly be able to use it to produce fascinatingvisual effects.

To use Lab mode, convert your imageusing the Image > Mode > Lab Colorcommand or the Edit > Convert to Profiledialog. Most images have sufficient contrastand are clearly visible in all three RGBchannels, whereas the shapes in a Lab modeimage are only really visible in the L channel.The a and b channels usually appearextremely pale and contain almost norecognizable detail.

The way Lab mode works becomes moreapparent when you take a look at the Curvesdialog produced by your image (see theillustrations on page 112). The graph for the L channel displays values from 0 (black) to 100(white), while the scale in the a and b channelsranges from -128 to +127 with zero in the

For minor adjustments, such as the local tonal adjustment we applied to this cat portrait, using blending modes as direct tool settings can significantly speed up your worflow



110


middle. The a channel represents themagenta/green component and the b channel blue/yellow. The negative valuesstand for the cooler green and blue tones,while the positive values represent thewarmer magenta and yellow tones. Here, azero value represents a neutral gray tone, thelightness of which is determined by it L value.Positive a and b values are brighter thanneutral gray, while negative values are darker.These relationships are the secret of the Labmodel.

But lets get back to blending modes. Theseparation of lightness and toneincorporated into the Lab model makes itpossible to adjust a color without affectingits brightness by applying blending modesto the a or b channels only an approachthat is simply not possible in RGB and CMYKmodes, where adjustments to color alwaysaffect brightness.

Using Calculations to Adjust Colors

In the following example, we will be using theb channel of an image to apply a Calculationsadjustment (Image > Calculations) using oneof the blending modes from the fourth group(i.e., the ones that do not change a photosoriginal neutral gray tone). Merging either thea or the b channel with itself intensifies thecolors in the image that correspond to thatchannel.

There are many more color variations tobe discovered if you invert the source pixelsin the Calculations dialog (select the Invertcheckbox in the Source 1 section) or blendthe L channel in Normal mode with one ofthe color channels. It is easier to gain animpression of the results these types ofblends will produce if you hide the channelyou are not working on by clicking on theeye icon in the Channels panel. You can nowblend the L channel into your target colorchannel by selecting it as your source. Thisconverts all the image elements that aredarker than neutral gray to green (if you areusing the a channel) or blue (if you areworking with b). Correspondingly, all theelements that are brighter than neutral grayare converted to magenta in the a channeland yellow in the b channel. All of theadjustments mentioned here can be fine-tuned by adjusting the opacity level.Using Calculations is a quick way toselectively intensify colors and is a popularmethod for pepping up images captured indull weather. But remember, color data hasto be present in the first place if it is to beintensified, so check the content of the

image areas you want to adjust using theEyedropper tool in the Info panel beforeapplying an effect.

Adjusting Colors usingAdvanced Blending Options

To try out this technique, first duplicate thebackground layer of your Lab mode imageand double-click the new layer icon to openthe Layer Style dialog. Then uncheck the L channel in the Advanced Blending sectionof the dialog to ensure that the blending

mode you select in the General Blendingsection is only applied to the two colorchannels. In our garage door example onpage 113, we used Linear Light mode.

You can, of course, further tweak youreffect by unchecking one of the colorchannels and/or adjusting the Blend if optionsto apply your blend effect to just part of theselected channel(s). The possibilities arevirtually endless and your imagination is theonly limit to what you can achieve. And by theway, you can apply the same technique inreverse to adjust the brightness of an imagewithout affecting its colors. (pen)



111


Applying a vignette with reduced opacity produces subtle effects that arequite difficult to detect but are nevertheless very effective

The channel views for a Lab mode image are unusual if you are used to viewing RGB images. Although the L channelcontains most of the visual information you would expect, the a and b channels do not appear to contain any visible data.

The L channel has values that range from 0 to 100, whereas zero is located in the middle of the color curves


Blending Modes for Photographers | Lab Mode

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Blending Modes for Photographers | Lab Mode

With just a few clicks in the right places, you can alter thecolors in a Lab-mode image without affecting brightness

Use the Blend if options to specify which colors remainunaffected by your changes c


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Blending Mode Slayer Tech