Photoshop Lab Color- P1 docx

Anybody would preferFigure 1.1B, which was created in approximately 30 seconds in LAB.When I first wrote about LAB, in a 1996 column, I used a canyon shot The Canyon Conundrum LAB has a r

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eep in Death Valley, land of desolation and summertime heat

in the high 120s, a narrow canyon holds several lessonsabout color, photography, human perception, and a power-ful digital imaging tool

Parts of the clayish soil contain mineral deposits thatcreate striking color variations, especially when the lighthits just right in the late afternoon The effect allegedly reminds somepeople of a painter mixing up the tools of his trade

So, it’s called “Artist’s Palette,” a considerable stretch These dull tintshave about as much to do with those found on the palettes of Renoir orRembrandt as this book does with animal husbandry But nothing seemsgreat or small except by comparison It’s such a shock to encounter green

or magenta dirt that it seems absolutely blazing next to the monotony

of the surroundings People stand and stare at Artist’s Palette for hours,seeing subtleties that cameras can’t record and imagining brilliant colorsthat cameras don’t think are there

We can leave aside the philosophical question of whether the reality isthese dull colors that the camera saw in Figure 1.1A, or the comparativelybright ones conjured up by the infinitely creative human visual system

The fact is, if this picture is a promotional shot or even something for anature publication, the original isn’t going to fly Anybody would preferFigure 1.1B, which was created in approximately 30 seconds in LAB.When I first wrote about LAB, in a 1996 column, I used a canyon shot

The Canyon Conundrum

LAB has a reputation for enormous power, yet virtually all reference materials that advocate its use illustrate its capabilities with a single class of image This chapter introduces the basic LAB correction method and explains why it is so extraordinarily effective—if you happen to have a picture of a canyon.

Figure 1.1 This Death Valley canyon is noted for its strangely colored clay Green soil like that on

the right side of this photograph is so unusual that people remember it as being greener than what the camera saw Canyon images are often used to illustrate the power of LAB correction (bottom).

1

from Capitol Reef National Park in Utah My

book Professional Photoshop goes around 100

miles to the south with a shot from

Canyon-lands National Park

Another Photoshop book illustrates its LAB

section with a shot from Bryce Canyon

Na-tional Park A third uses a scene from Grand

Canyon National Park, and a fourth a canyon

from the Canadian Rockies And author Lee

Varis has a scintillatingLABexercise,

repro-duced here in Chapter 16, that brings out the

best in a canyon in North Coyote Buttes, on

the Arizona/Utah border

Start to detect a pattern?

Yes, indeed LABdoes really, really well

with canyons And you don’t even need to

know how it works to make the magic

hap-pen; the approach to canyons is simplicity

itself Figure 1.1B isn’t the best we can do in

LAB(we’ll be revisiting this image in Chapter

4, treating it in a slightly more complex way)but it’s much better than any comparablemoves in RGBor CMYK, and even if you couldmatch the quality in some other colorspace itwould take far longer

When I wheeled out that first canyon shot

in 1996, I likened LABto a wild animal: verypowerful, very dangerous That label hasstuck Use of LABis now widespread amongtop retouchers, but a huge fear factor limitsthe techniques they use it for Most of thosewho claim to be LABusers are only doingwhat’s described in the first five chaptershere, missing out on much magic

You can’t blame them for being satisfiedwith what they’ve got, because those limitedLABtools can make an extraordinary differ-ence in image quality They are also so simplethat beginners can enjoy their benefits

I hope, and the publisher hopes harder,that people with limited experience will learn enough to dramatically improve theirpictures On the other hand, some of whatfollows either is unbearably complicated orsuggests methods that only power users canfully appreciate For the best of reasons, itisn’t customary for Photoshop books to cater

to novices and simultaneously include rial that leaves experts cursing in frustrationuntil they re-read it for the eighth time

mate-Special handling is clearly required

The Rules of the Game

Each of the first six chapters is divided intotwo parts, readily identifiable by a change

in typeface If you’re just trying to get intoworking with LABas quickly as possible, youcan skip the second part of each chapter,which is more analytical, and can be some-what difficult to follow

Figure 1.2 Like Figure 1.1, this image features colors

that are possibly accurate, yet too subdued when taken

in the context of the scene This canyon is called

“Yellowstone” for a reason The yellowness of the canyon walls should be played up.

For efficiency’s sake we will bypass twocustomary procedures First, a few para-

graphs ago, I did something that I find

exceedingly irritating when other authors try

it I asserted that a certain way of doing things

is better than the customary alternative, and

expected you to take it on faith Yet, if I

had stopped to prove that straight L A B

correction indeed yields better results than

RGB in canyon images, there would have

been an eight-page detour

So, in the interest of speed, the first half ofeach chapter concentrates on the how, not

the why I will say things that might be

labeled matters of opinion without stopping

to prove they are so Take my word for them if

you like; if you’d rather not, they are backed

up in the “Closer Look” section

Also, the first halves don’t assume muchPhotoshop expertise I try to give simple

explanations of each command being used

The second parts play by no such rules, and

often dive right into techniques familiar only

to a sophisticated audience And they don’t

offer many explanations of Photoshop basics

LABis always an intermediate step Filesmust be converted into it before the fun

begins and out of it afterward Almost

every-one will be converting into LAB from an

RGBfile When finished, some will convert

back to RGBand others, needing a print file,

will go to CMYK For the time being, it doesn’t

matter which; we will assume for

conve-nience that it goes back to RGB Your

defini-tions of RGBand CMYKin Photoshop’s Color

Settings dialog don’t matter yet, either We’re

now ready to tackle some canyons

It would take a wheelbarrow to carry every

way of defining color that’s been propounded

in the last century Our current LABis one of

the most prominent, an academic construct

designed not just to encompass all able colors (and some that are imaginary, afascinating concept that we’ll explore atlength later, notably in Chapter 8), but to sortthem out in a way that relates to how humanssee them

conceiv-The version of LABused in Photoshop wasborn in 1976, child of a standards-settinggroup called the International Commission

on Lighting and known by its French tials,CIE

ini-There have been several close relatives

We need know nothing about them, but colorscientists feel that we should use a moreprecise name for our version They call itCIELABor L*a*b*, both of which are a pain topronounce and maddening typographically

Photoshop calls it “Lab color,” but the namehas nothing to do with a laboratory: the Lstands for luminosity or lightness; the Aand

The Canyon Conundrum 5

Figure 1.3 A more vivid version of Figure 1.2, prepared

using the LAB recipe of this chapter

Bstand for nothing The name should be

pronounced as three separate letters, as we

do with other colorspaces

We need not concern ourselves with LUV,

LCH, xyY,HSB,XYZ, or other color definitions

(at least until Chapter 13), because

Photo-shop fully supports only three:CMYK,LAB,

and RGB Pretty much everybody has to use

either CMYKor RGB; increasingly people are

being called upon to use both

All printing is based on CMYK, although

most desktop color printers either encourage

or requireRGBinput Web, multimedia, and

other display applications require RGBfiles

Commercial printers want CMYK But LAB

files are usually unwelcome, except in

Photo-shop, Photo-Paint, and other specialized

applications A few raster image processors

(RIPs) for printing devices also claim to be

able to handle LAB, but gambling that they

actually do is a sport for the dedicated player

of Russian Roulette

Although LABis a distant relative of HSB,

which has been used as a retouching and

color correction space on many high-end

systems, such as Quantel’s Paintbox, nobodythought that people would be perverseenough to use LAB for such purposes inPhotoshop Instead, it’s there as a means ofexpediting color conversions

The language of color is notoriously precise If you work in RGB, 255R0G0Bdefinespure red Unfortunately, there’s no agreement

im-as to what pure red means Anybody needing

to know exactly what kind of red you intendwould have to find out what your PhotoshopColor Settings are, because there are differentdefinitions of RGB, each of which has its own idea of what constitutes red There is,however, only one Photoshop LAB

If you wish to order a car in a differentcolor than the model you test-drove, it won’t

be sufficient to say you want a red one Beforeaccepting your money, the dealer will insistthat you look at a swatch book to make sureyou get the red you expect You won’t hearanything about LAB, but the supplier of thevehicle’s paint will, if you complain that the color doesn’t match and the car manu-facturer agrees with you It wouldn’t do for

Figure 1.4 Photoshop defaults (left) look slightly different than the curves in this book (right) In the gradient at

the bottom of the grid, note that the LAB default has darkness at the left (in agreement with the Photoshop RGB

default), but this book uses lightness at the left, which is the default for CMYK and grayscale images To reverse the

orientation, click inside the gradient bar below the grid Also, the default uses gridlines at 25 percent increments,

whereas the book uses 10 percent intervals To toggle between the settings, Option– or Alt–click inside the grid.

the manufacturer and the paint supplier

to scream and wave swatch books in each

other’s faces They specify LABvalues, plus a

tolerance for how far off the paint can be

In the event of a dispute, they whip out a

spectrophotometer and measure its color

If the manufacturerhires you to produce

artwork that represents thatcolor, you’ll be getting the LABinformation as well, just asPhotoshop gets LABvalues fromPantone, Inc., that enable it toconstruct the P M S (PantoneMatching System) colors thatare the de facto standard in thegraphics industry

Assembling the Ingredients

We will start with, shockinglyenough, a canyon You can fol-low along with the image on theenclosed CD, or you may useone of your own, provided thatyou think you understand whycanyons make such great LABfodder Regrettably, there’s more to life thancanyon shots And just as LABdoes extremelywell on certain classes of image, it doespoorly on others Much of this book is aimed

at showing how to distinguish such images

If you do choose to use your own image,

The Canyon Conundrum 7

Figure 1.5 Measuring the lightness range of

the interest object After the file is in LAB , call

up the Curves dialog and, with the Lightness curve open, click and hold the mouse over an important part of the image A circle appears

on the curve, indicating the value of the point underneath the cursor If you move the cursor around the interest object with the mouse button still depressed, the circle will move with it The tonal range of the canyon walls falls between the two diagonal lines.

Figure 1.6 The LAB curves

that produced Figure 1.3.

Note how the L curve has

been made steep in the area

indicated in Figure 1.5 The

A and B channels have also

been steepened, by rotating

them around the unchanged

midpoint.

three types should be avoided First, the

image should not contain colors that are

already brilliant or highly saturated Second,

it shouldn’t have an overall color cast If you

think that the Figure 1.1A is too gray or too

blah or whatever, fine, but if you think it’s

too blue, you won’t be able to fix it without

reading Chapter 4 And third, nobody should

have applied unsharp masking yet

Figure 1.2 seems to qualify It hasn’t been

sharpened; there’s nothing even close to a

bright color in the canyon, and the clouds

appear to be white, not some goofy hue that

would indicate a cast

Also, it appears to be just thekind of image we’re looking for,needing a color boost nearly asbadly as the Artist’s Palette of Fig-ure 1.1 did The canyon walls hereare slightly off-gray Not nearlyenough, however, considering thatthe most famous national park

in the world bears the name ofthat particular color, for this is apicture of the Grand Canyon of the Yellowstone

The following recipe for ing out the colors that are hidden

bring-in such images will be refbring-inedconsiderably in coming chapters

But to get started on mak ingsomething more convincingly yel-low, like Figure 1.3, make yourself

a copy (or a duplicate layer) of theRGBoriginal if you think you’d like

to have something to compareyour work to afterwards

Next, Image: Mode>Lab color

The picture should look no different, but theidentification bar at its top should now readLab rather than RGB

Call up the Curves dialog with Image:

Adjustments>Curves (keyboard shortcut:

Command–M Macintosh; Ctrl–M PC) Ifyou’ve never worked in L A B before, thePhotoshop default treatment of lightness-to-the-right is probably still in effect Althoughthere’s no technical advantage either way, thisbook uses lightness-to-the-left, so you shouldprobably change over now by clicking insidethe gradient bar at the bottom of the curve, asshown in Figure 1.4

Figure 1.7 In LAB , unsharp masking must be applied to the L channel only, and should be evaluated with the screen display at 100% view The numbers shown here can be used as defaults, but better results can be had by customizing them

to the specific image.

Also, the default curve box has gridlines

at 25 percent increments, a little coarse for

serious work Option–click (Mac; Alt–click

PC) inside the box, and the grid changes to

10 percent increments

Having made these cosmetic changes tothe interface, we proceed to the recipe

A Canyon Correction, Step by Step

• Click into the word Lightness above the

curve grid and change it to a Move the top

right point of the curve one gridline to the

left; that is, a tenth of the way toward the left

axis Move the bottom left point one gridline

to the right The two points must be moved

an equal amount, because the resulting curve

needs to pass over the same center point as it

did originally

• Without clicking OK, switch over to b,

and apply the same changes In both

chan-nels, we’re making a steeper line by, in effect,

rotating it counterclockwise around the

center point

These two moves are the ones unique toLAB, the ones that drive colors apart from

one another in a way that other colorspaces

can’t equal What comes next could be done

elsewhere So, stop now, clickOK, and return

to RGBif you must—but you should really

leave the dialog open, and try to complete

the magic in LAB

The following two steps can be modified totaste if you’re comfortable with curves and/or

sharpening settings

If you’ve never worked on the A and Bchannels before, then you’ve never worked

on anything like them before On the other

hand, if you know how to apply curves to a

grayscale document, then you know how to

apply them to the L We’ll discuss the concept

further in Chapter 3, but it boils down to this:

the steeper the curve, the more the contrast

Your task is to make the part of the Lcurve

that encompasses the canyon steeper than

the rest

• Before clicking OK, switch to the ness curve Move the cursor back into thepicture over part of the canyon, and click andhold While the mouse button is depressed, acircle appears on the curve, indicating wherethe point under the cursor is located Stillholding the mouse button down, move thecursor to various parts of the canyon, andnote the range where the circle is moving InFigure 1.5, I’ve inserted red lines to indicatewhere on the curve most of the pixels repre-senting the canyon are located That area ofthe curve has to be made steeper Sometimes

Light-we do this by inserting points where my redlines are and lowering one while raising theother Here, I simply raised the center of thecurve, as shown in Figure 1.6

• Apply the curves by clicking OKin thedialog Now, display the Lchannel only, either

by highlighting it in the Channels palette or

by using the keyboard shortcut Command–1(Mac; Ctrl–1 PC) Then, Filter: Sharpen>

Unsharp Mask If you are familiar with how the dialog in Figure 1.7 works, you’ll have

a good idea of what numbers to enter If not, enter Amount 200%, Radius 1.0 pixels,Threshold 10 levels, understanding that betterresults will be possible after you’ve readChapter 5 Hit OKand compare it to the orig-inal If satisfied, return the image to RGBifthat’s what your workflow needs, or convert it

to CMYK, as I did for this book

Finding Color Where None Exists

The first two steps established the color ation that gives LABits reputation for realism

vari-The third added snap, and the fourth ness If you are considering how this mighthave been done in RGBorCMYK, the bottomline is that Steps One and Two aren’t easy toduplicate Step Three happens to be easier forLABin this particular image, but in other im-ages there’s no advantage Step Four is some-times better done in LAB, although this time

sharp-it could be done equally well elsewhere

The Canyon Conundrum 9

But working in LABis fast, fast, fast Once

you get the hang of it, it should take about a

minute to get this kind of result with a canyon

image Let’s try another

Figure 1.8 comes from a substantially

nas-tier clime than Yellowstone It’s Anza-BorregoDesert State Park, one of the hottest places inthe world Located in Southern Californiajust a short way from Mexico, it enjoys sum-mer temperatures that rival Death Valley’s

Rainfall is a pitiful inch ortwo each year

Such conditions aren’texactly conducive to plantlife The scraggly ocotillo

in the foreground at rightwill wait patiently for fiveyears or so for enough win-ter rain to permit it to blos-som into orange and greensplendor The rest of thetime, it sits and awaits de-velopments, clothed in abrown as drab as the back-ground This canyon wascut not by a river, but byrepeated flash floods, be-cause when the rain does

f all, the ground is tooparched to absorb it

When you or I visit such

an area, we don’t find itparticularly colorful but wecertainly see more than themonochromatic mess thatany camera would When-ever we look at a scene ofsubstantial ly the samecolors, our mind’s eyebreaks them apart, creat-ing different levels ofbrownness in the rocksthat artificial instruments

Figure 1.8 The desert image at

top shows the lack of brilliant colors and the shortness of range that suggest an LAB correction.

Bottom, after a literal repetition

of the steps that produced Figure 1.3.

A

B

such as cameras lack the

imagination to envision

In other colorspaces, it’srare to apply exactly the

same move from one image

to the next But with the

speedy LABrecipe, it’s more

thinkable Figure 1.8B was

produced by a literal

repeti-tion of the steps that

pro-duced Figure 1.3 The result

is the same: dramatically

increased contrast and

color variation, in a way

that as far as I know can’t be

achieved in RGB

Customizing the recipe

to this image yields a

mar-ginally better result, as

shown in Figure 1.9 The

changes are two

First, the ABcurvesare twice as steep as

they were in the

Yellow-stone example That is,

rather than bringing the

bottom and top

end-points in by one

grid-line, the curves shown

in Figure 1.9 are moved

twice as much There’s no right answer as to

how much to steepen these curves, but it

does make sense that this image should have

steeper AB curves The Yellowstone image

was too flat, but it did have some color

varia-tion Figure 1.8A is pretty close to a sepiatone

The function of the ABcurves is to bring out

the colors This picture needs such surgery a

lot more than the Yellowstone image did

Second, a slight improvement is possible

in the Lcurve The two canyons were just

about the same darkness The Anza-Borrego

canyon occupies a slightly smaller range, so

the curve could be made a bit steeper But the

Yellowstone Lcurve works acceptably

A River Runs Through It

Finally, having run out of canyons, we’ll move

a few miles to the south of Figure 1.3, ontothe shores of majestic Yellowstone Lake Fig-ure 1.10A was taken in early morning, withuninspiring lighting and a bit of fog

In addition to great canyon work, LABmelts fog like a blowtorch does butter Again,we’ll show a version (Figure 1.10B) made byexact repetition of the procedure that createdFigure 1.3 For the customized version (Figure1.10C), instead of doubling how far we took inthe ABcurves, as in Figure 1.9, it’s tripled—

the top and bottom points have each moved

in three gridlines

Figure 1.9 A second corrected version uses the curves shown below, increasing the

color variation by bringing the corners of the A and B curves in by twice as much as

in Figure 1.3.

B

How much to steepen the curves is asubjective call The four originals we’ve

looked at exhibit varying degrees of

color-lessness Personally, I feel that the

Yellow-stone Canyon image starts off better than the

others and needs less of a boost; the Death

Valley picture is second best; the

Anza-Borrego shot is next; and the worst of all is

this Yellowstone Lake image As the originals

got less colorful, I made the A B curves

steeper, always remembering to make them

cross the same center point on the grid

There is, of course, no reason why you

have to agree with the foregoing assessments

You can choose steeper angles for some oruse the same one each time And please re-member, this is the first chapter, discussingthe most basic move This recipe permits anamazing variety of modifications

The L curve is somewhat different herethan in the other examples we’ve looked at

The steep area is a bit longer, because thelake has a fairly long range—parts are light,and parts get almost to a midtone All three ofthe canyons fell in a very short range, both forcontrast and color

The Canyon Conundrum 13

Figure 1.10 Top left, this

orig-inal needs an extreme

steep-ening of the AB curves to

bring out color Bottom left, a

version done exactly as in

Figure 1.3 Below, a

customized version using the

curves at right, in which the

AB endpoints are brought in

three times as much.

C

Which brings us back to why authors use

canyon images to illustrate the power of LAB

The recipe works extremely well—provided

the subject is a canyon, or something with the

same characteristics By the same token, you

should now be able to imagine the type of

image in which the recipe would probably

not do so well.

These canyon shots have all featured

sub-tle colors What if they aren’t so subsub-tle? This

recipe makes all colors more intense If the

original colors were brilliant,LABis highly

effective at rendering them radioactive And

it is no coincidence that the most important

parts of all four images so far have fallen into

a relatively small range of tonality (darkness)

That isn’t the case with all or even most

pic-tures, and if it isn’t, these Lcurves won’t work

And that’s the basic LABcorrection, minusexplanations of why LABworks or how it’sstructured If you want that now, skip ahead

to Chapter 2 If instead you’d like a more nical explanation of why we like color varia-tion and why the best way to get it is in LAB,keep going, remembering that the secondhalves of chapters assume much more Photo-shop knowledge than the first halves do

tech-And a final reminder, once you’re donewith your LABmaneuvering: few outputdevices accept LABfiles, and few programsoutside of Photoshop will display them So,convert the file back to RGB, if you’re going topost it on the Web or send it to a desktop orother printer that requires RGB; or convertdirectly to CMYKfor commercial printing, as

I had to throughout this book

Review and Exercises

NOTE: Answers to this section, which appears in every chapter, are found in the “Notes & Credits”

section of this book, commencing on Page 351.

✓ Why is it important that the images we’ve worked with so far not start out with any obvious color

cast? What would probably have happened if they had?

✓ The images in this chapter are obviously selected to portray LABin its best light What do they

have in common? What types of images would you suspect might not be appropriate forLAB?

✓ What is the impact of making the ABcurves more vertical?

✓ What do you think would have happened if, instead of making the ABcurves more vertical by

rotating them counterclockwise around the center point, we had done the opposite, making

them more horizontal by rotating them clockwise?

✓ Do you understand how LABkeeps color and contrast as separate items? If in doubt, try redoing

some of these moves, once in the AandBchannels only, and once in the Lchannel only.

✓ Have you verified that your curves display darkness to the right as in Figure 1.4? If they don’t,

click into the gradient bar underneath the curves grid to reverse it.

✓ Try this method with some of your own images, or redo some of these images Try the effect of

steepening the AandBby different amounts, which we’ll be discussing in Chapter 3.

Michel Eugène Chevreul, a French

chemist, anticipated LABcorrection by

a century and a half in his seminal

1839 work, On the Law of Simultaneous

Contrast of Colors He tried to describe

something that is even today

inde-scribably complex—the propensity of

the human eye to break colors apart

from their surroundings The effect had

been known to some extent by the

an-cient Egyptians, and in the 15th century

Leonardo da Vinci indicated that he

understood it Three hundred years

later, the brilliant German poet Johann

Wolfgang von Goethe expounded on

it, and it took less than a century

there-after for Chevreul to fully flesh it out

Everybody is familiar with exampleslike those of Figure 1.11, which are

often described as “optical illusions.”

The term implies that a human

ob-server would have one opinion as to

whether certain colors or even sizes

were the same, and a machine

(includ-ing, bien entendu, a camera) would

have another

Simultaneous contrast is an old vival instinct, dating from the prehis-toric days when our ancestors wereobliged to forage for food in the forest,

sur-as they could not go to McDonald’s

Unfortunately, granted that we areforced to be hunters and gatherers, thedesign of our bodies leaves much to

be desired We don’t run very fast Wearen’t particularly strong We don’t fightwell We can’t climb trees easily Wedon’t have good senses of smell orhearing We don’t see well at night

We have impeccably designed hands,and what might be described, at leastuntil recent years, as superior intelli-gence, but still, we stack up poorly incomparison to, say, a tiger

Darwin advises that when a specieshas an advantage that enables it to sur-vive, that advantage gets selected forand therefore magnified over time

Start with an animal that can reachcertain edible leaves that others can’t,because its neck is longer; give it a fewmillion years and you get a giraffe

A Closer Look

Figure 1.11 The surroundings influence human perception.

Above, are the two red objects the same color, or is the bottom set lighter and more orange? Below, are the two magenta circles the same size? Humans and machines would disagree on the answers to both questions.