Raw Getting Started

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Where the Bits Are:Linear vs. Nonlinear DataChapter 2 touched briey on the act that your eye and your camera

respond to light levels in very dierent ways. I you double the amount olight being shined at your camera, then your camera will record a 200 per-

cent increase in illumination. Because a cameras response to light is directly

proportional to the intensity o the light source, we say that it has a linear

response to light.

Your eyes dont work this way. Your eyes are much more responsive to sub-

tle variations in bright and dark tones than they are to changes in midtones.

In other words, their response to light is not directly proportional to the

intensity o the light source in question. Thus, we say that your eyes have a

nonlinearresponse to light.

Like your eyes, flm has a nonlinear response to light. As you saw in Chapter 2,

when you shoot with your camera in JPEG mode, agamma correction curve is

applied to your image to make its luminance response more closely resemble

the nonlinear perception o your eyes. Because JPEGs gamma correction yields

a light response that is similar to the response o flm, any exposure habits that

you have rom shooting flm will most likely still apply.

When you shoot in raw mode, though, things work very dierently. When

you shoot in raw mode, your camera records a lot more data or brighter

tones than it does or shadow tones.

Twice the data in half the stops

As youve probably already noticed, many o Camera Raws controls seem to

do the same thing. With the Exposure slider, you can brighten or darken an

image, but you can also brighten an image with the Brightness control and

darken it with the Shadows slider. Understanding how your digital camera

captures dierent tones will make it easier to understand which control to

use or a particular adjustment.

I your digital camera uses 12 bits o data per pixel, then its capable orepresenting and processing 4,096 dierent levels o brightness. In a digital

camera, halo those 4,096 levels go toward recording the brightest stop,

hal o the remaining levels go to recording the next-brightest stop, hal

o whats let rom that go into the next-brightest stop, and so on or the

remaining stops that your camera can capture. There is a straight, linear

halving o data or each stop.

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192 Chapter 6 : Advanced Edit ing in Camera Raw

Figure 6.9 Most o the data

your camera captures goes

to recording the brightest

hal o the image. Hal o

the remaining data then

goes to recording the next

stop, and so on. This means

that your camera records

substantially more inorma-

tion or the bright areas o

your image than or the

dark areas.

By the time your camera gets down to the darkest stop (usually the shadow

areas o an image), it may have only 64 levels let that it can use to represent

your darkest shadow details (Figure 6.9). A less pessimistic way o looking

at things is to say that i you expose or the highlights, then you ensure that

your camera encodes your image with the maximum number o brightness

levels. (Well discuss how to perorm this type o exposure in Chapter 7.)

As youve already seen, where theres less image data, theres a greater

chance that posterization and tone breaks will occur when you make

edits and adjustments. Because the camera captures so much data or the

brighter stops, i you expose to capture as much inormation as possible

rom these areas, youll have a tremendous amount o data to work with

when you edit. This means that youll be able to make large adjustments

without ear o posterization.

Conversely, i you underexpose, then youll be capturing more data in the

midtones and shadow parts o the cameras rangeareas that arent rep-

resented by a large number o levelsand so you will have less editinglatitude (Figure 6.10). When you brighten this underexposure, youll almost

certainly reveal noise thats been hiding in the shadow parts o your image.

To speak o this using terms that you learned in Chapter 3: Youve seen that

when you make a Levels or Curves adjustment or use the exposure sliders in

Camera Raw, you are compressing or expanding dierent parts o the data

in your image. Since your camera captures so little data in the shadow areas,

expanding the shadows is a verybad idea, as it will almost always lead to

posterization (since theres not much data there in the frst place). Expanding

the data-rich highlights into the shadow areas poses ar less posterization

risk, and because theres so little shadow data there to begin with, theresvery little risk that youll be compressing data thats already there.

You dont necessarily have to overexpose your images to perorm this kind

o capture. I your camera has a good light meter, youll be shooting with

exposures that yield very good data. However, your cameras metering

system is probably optimized to yield exposures that are best or gamma-

corrected JPEG images. Thus, many meters oten err on the side o slight

underexposure. While your meter will oten be right, its important to keep

an eye on what its doing. Well discuss this subject more in Chapter 7.

2,048 levels

1,024 levels

512 levels

256 levels

128 levels

64 levels


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I youre coming rom a flm background, where youre used to under-

exposing to protect your shadow detail, youll have to retrain yoursel.

Underexposing when shooting raw is a badidea. With digital raw photog-

raphy, you want to expose to capture as much highlight detail as you can.

Youll correct or your shadows later.

Figure 6.10 The image on the let was slightly underexposed. Though the shadows arent

clipping and it has an acceptable range o contrast, it has very little data in the highlight

areas, the areas where your camera captures the largest number o tones. The image on

the right has a lot o highlight inormation, meaning that its a data-rich image that can

withstand a lot o editing and adjustment.

Where the Bits Are: L inear vs . Nonlinear Data


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Measuring in stops

I you have even cursory photographic experience, youve probably

heard the term -stop. There are two mechanical mechanisms inside your

camerathe shutter and the aperturethat control the amount o light

that strikes the image sensor. When you change the shutter speed rom

1/125 o a second to 1/60 o a second, you double the amount o light that

strikes the ocal plane, because the shutter is kept open or twice as long.

Similarly, when you change the aperture rom /8 to /4, you double the

amount o light that strikes the ocal plane because the size o the aper-

ture at /4 is twice as large as at /8. (Obviously, moving the other direction,

rom 1/125 to 1/500 or rom /8 to /16, results in a halving o the light.)

Each o these doublings (or halvings) o light is reerred to as a single

stop, and youll oten hear photographers using the word stop as a mea-

sure o light. A simple way to think about -stops is to remember that a

smaller aperture stops more light rom hitting the ocal plane, as does

a aster shutter speed.

For example, say youre shooting in a somewhat dark situation and your

cameras light meter recommends an exposure o 4 at 1/30 o a second.

That shutter speed is a little slow to be shooting hand-heldtheres a

good chance that your image will be sot or blurry at 1/30 o a second. Lets

assume that ash is inappropriate in this situation. Lets also assume that

you have a piece o white cardboard with you, which you use as a reec-

tor to bounce some light onto your subject. Now when you check your

meter, your camera recommends /4 at 1/60 o a secondthats a shutter

speed thats twice as ast as what the camera was recommending beore.

With your reector, youve just added an entire stops worth o light to your

scene and so now have an exposure more suited to shooting handheld.

Every doubling o light can also be reerred to as one exposure value, or

EV. Photographers oten use EV to denote over- or underexposure without

having to concern themselves with specic aperture and shutter speed

values. So i two photos dier in exposure by 1 EV, then one o them was

overexposed by 1 stop, through a change in either shutter speed or aper-

ture (or possibly, by a change o hal a stop in both parameters).

The human eye has a dynamic range o 30 -stops o lightrom ully

adapted night vision under starlight to brightest daylightabout a ac-

tor o 1 billion to 1. The typical digital camera (or lm, or that matter) has

a range o 8 to 10 -stops o light (or 8 to 10 EV). Some natural scenes have

a range o 12 -stops (or EV) between the brightest highlights and deep-

est shadows. The act that the dynamic range o camera technologies is

so much smaller than that o your eye is one o the reasons that photog-

raphy can be tricky. Your camera oten cant record the ull dynamic range

o the scene, or what your eyes can see, so you have to make choices

about which 8 to 10 -stops you want to capture.


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Reading it in the histogramFrom what youve already learned about reading

a histogram, you know that when you darken an

image, the bars in your histogram shit toward

the let. This happens because, ater your edit,

there are ewer bright values and more midtoneand dark values. Similarly, i you brighten an

image, the bars in your histogram shit toward

the right.

I youve exposed an image to try to capture

as much data in the highlights as possible, your

histogram will have a distribution thats heavy

on the right, like the one shown in Figure 6.10.

Such an image may appear washed out, or too

bright. However, because you have so muchimage data, you can easily darken some o those

captured levels to produce an image that looks

better. In the resulting image, the data will appear

to have been pushed down into the shadows

(Figure 6.11).

With all o this in mind, some o the seeming

overlap in Camera Raws controls should make

more sense, as youll see in the next section.

Going Furtherwith Raw ControlsChapter 4 introduced you to Camera Raws white

balance and exposure control tools. These seven

sliders are where the bulk o your raw editing

work takes place. In this section, youre going

to take another look at these controls, but thistime ramed within your new understanding o

nonlinear data.

Figure 6.11Ater the right image in Figure 6.10 has been

adjusted, the histogram shows tones that have shited to

the let. Weve darkened some o the bright tones to place

them in the middle and shadow areas.

Going Further with Raw Controls


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Adjusting white balanceYouve already seen how to use the Temperature and Tint sliders and the

White Point tool to adjust the white balance o your image. Although accu-

rate white balance is great or achieving a aithul reproduction o the colors

o a scene, sometimes an image will look better, or more evocative, i it

has an extra bit o warmth or has been cooled down a little. Both o theseeects are easy to achieve with temperature and tint adjustments.

For example, Figure 6.12 shows three images created rom the same raw

fle. The only thing that changed or each image was the Temperature set-

ting in the Camera Raw dialog box. The top image uses the cameras auto

white balance selection, which is airly accurate, given that the photo was

shot on a stage with very warm lighting. The middle image is much warmer,

and the bottom image is very cool. Depending on the mood you are trying

to evoke or the color palette o other images or graphics that you plan to

use alongside your image, one white balance may be more appropriate than

another.

Though you can warm up images using the Curves and Hue/Saturation tools

in Photoshop, the Temperature control in Camera Raw is usually a better

choice because it properly adjusts allo the tones in your image. Trying to

warm an image with most regular editing tools means spending some time

adjusting all three areas o an image: highlights, midtones, and shadows.

With a white balance adjustment, you get it all at once.

Adjusting exposureChapter 4 introduced you to Camera Raws Exposure tool, which is analo-

gous to the white point tool in the Levels dialog box. With it, you defne

what the brightest point in an image is, and all o the other tones are

remapped accordingly.

As discussed in the previous section, the brightest stops in a raw image

contain the most data. I youve done your shooting job well, then most

o your Exposure slider moves will be to darken an image, because you will

have tried to capture more rom the brighter stops, to collect more data. I

you fnd that you need to use the Exposure slider to brighten an image, its

not the end o the world. Your image is not useless, and its not ruined

theres just a better chance that your shadow detail will be posterized or

noisy ater your adjustments.


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Figure 6.12 You can alter the eel

o an image by changing its white

balance. The top image shows the

cameras automatic white balance.

The middle image has had a much

warmer white balance applied in

Camera Raw. The lowest image shows

a much cooler white balance. None o

these images is right or wrong, but

they have very diferent eels.



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Nevertheless, because its your key to remapping the data-rich bright parts

o your image into the midtones and shadows, the Exposure adjustment is

the most critical o all o Camera Raws controls.

Throughout this book, youve been told o the horrible consequences that

result rom clipping your highlights and shadows, so you may fnd it a little

odd now to be told that i you try to expose all your shots so that theyre

really bright, youll be much happier. Shouldnt you pay attention to what

your light meter says?

Absolutely. When taking this approach, you willrun the risk o clipping your

highlight values. Fortunately, Camera Raw has a airly amazing capability

that can help you with this trouble.

Using the highlight recovery function

As you saw earlier, ully clipped highlights are represented on Camera Raws

histogram by a white spike at the right edge. However, only one or two

channels o a pixel may be clipped; Camera Raw displays each o these

as a rightmost spike in the color o the clipped channel (Figure 6.7).

First the bad news: A completely clipped highlight is oten a bad thing.

It will appear in your image as complete white and will contain no detail,

and theres nothing you can do about it except hope that you shot an

additional, properly exposed rame.

A partially clipped highlight, though, is another story. I your highlights

are only partially clipped, theres a good chance that Camera Raw can

recover them.

Consider the image in Figure 6.13. As you can see rom the histogram,

the blue channel is heavily clipped, the green is barely clipped, and in a ew

places all three channels are clipped. (The spike on the right side is blue on

top, with a tiny bit o green below and then some ull white.)


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Figure 6.13 This image has partially clipped highlights, as you can see rom the right side

o the histogram. In the clipping display, you can see that the clouds sufer rom a lot o blue

channel clipping as well as some ull-blown three-channel clipping.



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By sliding the Exposure slider to the let, you can darken those clipped high-

lights back into tones that can hold detail (Figure 6.14). In other words,

areas that were previously empty white now show image detail.

Figure 6.14 I moved the Exposure slider to the let while keeping an eye on

the histogram. When the spike completely disappeared, I let go. As you can

see, the result is a 0.75-stop exposure. Though a lot o the image is darker,

those areas can be brightened with the Brightness slider. The important

thing to notice is how much more detail there is in the oggy areas o the sky.

This type o highlight recovery is not possible with any o Photoshops nor-

mal tools, and its another advantage o shooting raw. It also provides you

with a little saety when exposing. The act that Camera Raw can recoversome clipped highlights gives you a little more exposure latitude.

Highlight recovery is accomplished using several techniques. Some camera

manuacturers actually include a little headroom above their set white point.

This means that the camera actually captures a little more data that it claims,

and i this data is present, Camera Raw can simply grab it and use it to

remap the clipped highlight tones.

Camera Raw can also use the data in one o the surviving channels to

rebuild the missing clipped channel.

In the previous example, the histogram indicated that some tones wereclipped in one channel, and others were clipped in all three. Fortunately,

none o the clipping was so extreme that Camera Raw couldnt rebuild

those areas. At other times, you may fnd that Camera Raw can pull back

some o your clipped highlights, but not all, as shown in Figure 6.15.


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Figure 6.15 The upper image has

badly clipped highlights. With the

Exposure slider, we can recover a

lot o detail in the clouds, but no

matter how much we move the

slider to the let, those completely

blown sections o the sky will

remain white and unrecoverable.



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When making a big Exposure slider move to recover highlights, be sure

to keep an eye on the shadow end o your histogram as well. Youll need

to balance the amount o highlight inormation that you want to recover

against how dark youre willing to let the shadows in your image go.

Camera Raws highlight recovery unction is not just a handy tool or coping

with highlight clipping. Its also a saety net that allows you to expose or the

right end o the histogram, to try to capture as much data as possible. I you

dont know how to control the exposure on your camera, dont worrywell

cover that in detail in the next chapter.

Adjusting shadowsYou previously learned that the Shadows slider works just like the Black

Point slider in Levels (it defnes the darkest point in the image and remaps

all other tones accordingly), and your understanding o the role o the

Shadows tool is hopeully a little more sophisticated now that you knowmore about the nonlinear nature o raw fles.

Generally, since the shadow areas o an image contain so little data, its best

not to make large movements o the Shadow slider lest you risk introducing

posterization and noise into the shadow parts o your picture. Obviously, i

you chose an exposure that yielded very low contrast, youll have nothing to

lose by darkening the blacks in your image with a Shadows adjustment. On

well-exposed images, though, you should use the Shadows slider sparingly.

Adjusting brightnessI youre ollowing this expose or the highlights philosophy, then youve

probably started to realize that the brightness o your images will usually

not be too much o an issue. The bulk o your correction will be perormed

with the Exposure slider, which youll probably use to darken the image.

However, i youve had to perorm any highlight recovery, as discussed ear-

lier, youll probably end up with an image thats a little dark. As you saw in

Chapter 4, the Brightness slider lets you adjust the midpoint o an image,

just like the Gamma slider in the Levels dialog box; it brightens the mid-

tones without moving the white point (Figure 6.16).


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Figure 6.16Ater the Exposure slider was moved to the let to recover the highlights in this

image, the picture was too dark overall. We cant brighten the image using the Exposure

slider, or well reclip the highlights. Shiting the Brightness slider to the right restores bright-

ness to the midtones.

Figure 6.16 is a good example o the choices you sometimes have to make

when editing. A airly heavy Brightness adjustment is needed to restore

brightness to the image. Theres a good chance that this will cause some

posterization in the shadows. I the negative Exposure move had been less

aggressive, the image wouldnt need such a strong Brightness adjustment,

but then we couldnt recover as much highlight detail in the clouds. In thiscase, we decided that having the well-rendered clouds is worth any damage

we might be doing to the shadows in the image.

In general, highlight troubles are more noticeable than shadow troubles

simply because highlight troubles are easier to see. I a shadow is dark and

murky, its not too conspicuous, but a bright area thats lacking detail and is

blown out to white is easy to spot.

The trouble with this particular scene is that it has a huge dynamic range

thats difcult or the camera to capture. Thus, we have little choice but to

sacrifce either the shadows or the highlights.



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I you simply have an image thats too dark, then youll need to decide i

you want to brighten it with the Exposure slider or the Brightness slider.

When brightening an image, you should move the Exposure slider as little as

possible, to keep rom brightening the shadows too much. Set the Exposure

slider to get your whites adjusted properly; then use the Brightness slider

to brighten your shadow tones. Though you may not be able to tell a dier-

ence in the results, the Brightness slider will probably pose less o a poster-ization threat to the shadow areas o your image.

Adjusting contrast

The Contrast slider perorms two adjustments: it brightens the tones above

the midpoint, and it darkens the tones below the midpoint. (I youre

used to making corrections using Photoshops Curves controlas shown

in Chapter 3this is the same type o adjustment that you get when you

apply an S-shaped curve.)

In general, the Brightness and Contrast sliders work very well together. Use

the Brightness slider to add brightness to your image, and then use the

Contrast slider to punch up the image with a little contrast (Figure 6.17).

Figure 6.17 With a very slight Contrast move, we can punch up this image a little bit.

We need only a small change since this image is already close to being too dark.


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reducing contrast

Youve read a lot in this book about how the

human eye is very sensitive to contrast, and how

the eye usually preers contrast in an image, but

sometimes an image can be too contrasty. The

most obvious example is a person standing inront o a bright window: The extreme contrast

dierence between the darkness o the persons

ace and the brightness o the window can make

the image difcult to read. Figure 6.18 shows

an image with harshly contrasting highlight and

shadow areas.

Though you can try to lower the contrast

o this image using Camera Raws Contrast slider,

this really isnt the best approach to solving

the problem. First, the Contrast slider cant

reduce the contrast by much, and second, itwill reduce allo the contrast (Figure 6.19).

I you have Photoshop CS or CS2, a better

approach is to use the Shadow/Highlight tool

(Image > Adjust > Shadow/Highlight). Shadow/

Highlight analyzes your image and perorms an

intelligent brightening o only the shadow areas.

The results are sometimes incredibly eective

(Figure 6.20).

Figure 6.18 This scene had more dynamic range than

the camera could capture, resulting in an image thats

too contrasty.

Figure 6.20 Photoshops Shadow/Highlight tool makes

short work o the contrast problem shown in Figure 6.8.

The deault settings bring out plenty o shadow detail

without compromising the highlights.

Figure 6.19 Camera

Raws Contrast slider

lets us reduce the

contrast, but it doesnt

let us go very ar. Also,

though it lightens the

shadows, it reduces the

contrast in the bright

areas. We need a better

solution.



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Contrast reduction is useul not only or correcting outright difcult

situations. It can also help when an image is properly exposed, but yields

just a little too much contrast, as shown in Figure 6.21.

Figure 6.21 Though well-exposed, the contrast in this image makes it just a tad

too harsh.

While this image isnt bad, the shadow on the underside o the seagull

is just a little too strong. In this case, lowering the contrast in Camera Raw

reduces the shadow and produces an image thats a little more evenly

exposed (Figure 6.22).

Figure 6.22 In this instance, lowering the Contrast slider in Camera Raw reduces

the intensity o the shadow on the underside o the bird, creating a gentler tonal

transition.


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Adjusting saturationWhile extreme adjustments to the Saturation slider can lead to posterization

o bright colors, in general Saturation is a airly harmless tool as ar as your

image data is concerned. Camera Raws Saturation slider is not signifcantly

dierent rom the Saturation slider provided by Photoshops Hue/Saturation

control, so it doesnt really matter i you make your saturation adjustmentsin Camera Raw or in Photoshop.

However, i you wait to make your saturation changes using a Hue/

Saturation adjustment layer in Photoshop, youll have a little more editing

exibility. In addition to perorming your saturation change in a nondestruc-

tive manner, youll be able to use layer masks to constrain the eects o

your saturation change. Youll learn more about this later in this chapter.

There are no real guidelines about saturation changes; its purely a matter

o taste. Some images are obvious candidates or saturation adjustments

because theyre low contrast and have weak color. Others are good satura-tion targets because they have strong color that can be made even stronger

with a little saturation boost (Figure 6.23).

Figure 6.23 The only change made to the rightmost image was an increase in the Camera

Raw Saturation slider.

Tip

You can also think of

Camera Raws sliders as

controlling the shape

of a tone curve. The

Exposure slider repre-

sents the upper-right

point, Shadows the

lower-left point, and

Brightness the midpoint.

The Contrast slider adds

two more points to the

curve to create a con-

trast-inducing S-shape.



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Some images beneft rom a reduction in saturation. Whether the subject

matter requires less garish color or youre trying to evoke a particular

mood, reducing the saturation o an image can create a very dierent

eel (Figure 6.24).

Figure 6.24 This image takes on a diferent eel with less saturation. Ater reducing thesaturation, I brightened the image a bit with the Brightness slider and then warmed it

some with the Temperature slider. The bottom image shows the result.

Documents

Raw Getting Started