Tài liệu Photoshop cs5 by Dayley part 27 potx

Part IIWorking with Camera Raw Images IN THIS PART Chapter 7 Camera Raw Basics Chapter 8 Processing Photos in the Camera Raw Workspace... C H A P T E R Camera Raw Basics IN THIS CHAPTE

Part II

Working with Camera

Raw Images

IN THIS PART

Chapter 7

Camera Raw Basics

Chapter 8

Processing Photos in the Camera Raw Workspace

C H A P T E R

Camera Raw Basics

IN THIS CHAPTER

Benefits of camera raw The Camera Raw workspace Setting preferences

Creating snapshots Exporting RAW images

Many of the higher-end digital cameras support a file format that is

commonly called camera raw If your camera supports this format and you are serious about creating great photographs, you proba-bly want to be shooting in camera raw

Is camera raw really all that? Well, when you capture a picture in the standard

JPEG format, the camera takes the image from the image sensor and processes

it before saving it to your memory card This reduces the file size, but it

dis-cards image information that could have been used to refine your photo

The camera raw format, on the other hand, saves the unprocessed file,

preserving all the image data, so you can process it manually later It’s like

being able to process your own negatives, tweaking them to get the color

and lighting just right

This chapter introduces you to the camera raw format, explaining why

cam-era raw is superior to JPEG and the advantages and disadvantages of using it

I also explain what a DNG file is and introduce you to the Camera Raw

workspace, explaining the tools and showing you how to set preferences

Benefits of Camera Raw—More

Is Better

Camera raw formats have been around for a few years now, and many

pho-tographers won’t shoot in anything else The ability to use all the image data

captured by the camera’s sensors, which amounts to trillions of colors, is a

heady feeling The fact that camera raw also stores your settings as metadata

Part II: Working with Camera Raw Images

that not only is always connected to your file, no matter where you go, but is also completely change-able is frosting on the cake If you’re wondering why all this should matter to you, I’ll explain

Original CMOS information—more bits

The sensors in your digital camera that register the light coming into your camera and convert it into a digital image are called CMOS (Complementary Metal Oxide Semiconductor) sensors Don’t worry; I’m not planning to remember that either The point is that when your camera is set to shoot JPEG images, your camera settings (such as the exposure or white balance) determine how the information is processed and everything that is considered extra data is discarded After the image is processed, it is compressed, further reducing the quality and size, to create a JPEG file

When you download that JPEG file onto your computer and make changes to it in Photoshop, every change further reduces the quality of your image

But that’s not the worst of it What happens to your photos when you’ve set your camera’s white balance to capture in fluorescent lighting and you forget to change it back as you step outside to get a few more shots? Not a pretty picture—and impossible to fix adequately with a JPEG image

A camera raw file, on the other hand, does not discard any of the information gathered by the CMOS sensors Instead, it processes it according to your camera’s settings, saves those settings as the default settings in the metadata, and then saves all the information gathered by the CMOS sen-sors as the image file

This can happen because cameras can capture as much as 14 bits per color channel, but JPEGs can store only 8 bits per channel Camera raw files, on the other hand, can store up to 16 bits per channel

With 8 bits per channel, each color channel can have 256 distinct tones Using 8 bits per channel allows an image file to contain over 16 million different colors With 16 bits per channel, each color channel can have 65,536 distinct tones Using 16 bits per channel allows an image file to contain trillions of different colors

You may be asking yourself if you really need that many different colors, especially since the human eye can detect only about 7 million colors at best But you’d be surprised at the difference using 16 bits per channel can have when adjusting levels on problem images The more tones per channel, the more options Photoshop has when adjusting the levels in an image For example, an image that is almost completely bleached out by overexposure or completely black from underex-posure can be salvaged into a printable form using 16 bits per channel

This means that more information is available to draw from than you can see in your image For instance, consider the first example shown in Figure 7.1 This photo is seriously overexposed At first glance, you might think that the photo doesn’t have enough pixel information to save it If it were a JPEG image, you’d be right; those pixels would be gone, or at least very faded

Lucky for me, this photo was taken in camera raw The pixel information isn’t missing; my camera was just set to a higher exposure than it should have been With a few tweaks in Adobe Camera Raw, I can readjust the exposure settings, in effect reinterpreting the information captured by the CMOS sensors and recovering most of the color information, as you can see in the second photo in

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191

FIGURE 7.1

Camera raw files contain so much more information than JPEGs that this photo was saved

On the Web Site

Open Figure 7-01 from the book’s Web site Can you recover the highlights? n

Non-destructive editing—more metadata

Changes made in a camera raw format are saved as metadata All photo files have metadata—

embedded information that tags along with the file Even scanned photo files have at least the date they were created and their size embedded as information that your computer can access and dis-play, even if your photo isn’t open in a photo-editing application Photos taken with a digital cam-era have a good deal more information You’ll find almost everything you want to know about an individual photo file—the date and time it was taken; what camera was used; if the flash was used, suppressed, or not needed; focal length; white balance setting; and the list goes on Figure 7.2 is just a sample of the metadata available for an image

Cross-Ref

Bridge displays metadata in its own panel You can find more information about metadata in Chapter 6 n

Part II: Working with Camera Raw Images

FIGURE 7.2

This is some of the metadata available for a camera raw image

In a camera raw file there is even more information I told you that even camera raw files are pro-cessed by your camera The difference is that the processing information is saved, not as the image file itself, as it is with a JPEG, but as metadata that is stored with the file

When you open a file in a camera raw format, it opens in the Camera Raw application that ships with Photoshop The version that comes with Photoshop CS5 is Camera Raw 6 This application allows you to make changes to your image, but unlike changes made to a JPEG image, these changes are not permanent, nor do they erode the quality of the pixels That’s because the changes you make are also saved as metadata

This is how it works If you’ve used Photoshop or another digital photo-editing application to change the exposure or color of your JPEG or TIFF photos in the past, you are going to be impressed by how clean and easy it is to change a camera raw image When you change the color

or lighting of a JPEG image in a standard editor, what you see in the photo is what you get In other words, the visible pixels are all you have to work with, and when you change settings such as the brightness or saturation, you actually alter the existing pixels in the photo file If you adjust the exposure a little too high, leaving areas of your photo completely white (specular highlights), that color information is irretrievable after you’ve saved the photo Other changes to your photo can leave “bruises,” eroding the quality as well as the believability of your photo

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Changing the settings of a camera raw image is very different You aren’t actually changing the pixels in the photo; you are simply changing the way the pixel information is interpreted by changing the meta-data Because there is so much more of that information than there is in a JPEG file, you have much greater latitude for interpreting that information You never lose color information in a camera raw file because if you set the exposure too high, it is always retrievable just by readjusting the settings

Note

Non-destructive editing holds true as long as you are processing your photo in Camera Raw After you open it

in Photoshop and make changes to it, you are required to save it in a standard image format The raw file isn’t

overwritten; you simply create a new JPEG, TIFF, or PSD file in addition to the raw file n

So mess with your camera raw files as much as you want If you go overboard with the settings, no worries; you can just hit the default button and everything goes back to the way it started You can

do this even after the file has been closed and reopened, or even if you are in a completely different camera raw editor You also can save your own settings as well as the default settings so they are retrievable even after you’ve made other changes to them

Drawbacks of Camera Raw—Size Matters

Okay, I’ll freely admit that you shouldn’t use camera raw for absolutely everything It’s not strictly necessary if you are taking a picture of your gaming system to post on eBay, for instance For one thing, you’ll just have to convert your photo into a JPEG in order to post it anyway, and that brings

me to the first drawback of camera raw

Camera raw is not universal

You’ve probably noticed that I’ve referred to camera raw formats I haven’t even shown enough

respect to capitalize camera raw That’s because it’s not a universal format—there are at least as many camera raw formats as there are brands of cameras that capture it It seems everyone wants

to design camera raw their own way Because so many formats are constantly being added, it’s hard

to find applications that read them Windows can’t even preview or display camera raw files with-out a plug-in, and eBay certainly doesn’t recognize any of them

It’s conceivable that some of these formats won’t stand the test of time and that 10 or 15 years from now, you won’t be able to open your camera raw files This is bad news for those of you who own laser discs! The difference is that instead of just having to spend more money on the same movie, you are losing your irreplaceable photographs

There is good news, however Even as more and more camera raw formats become available, Adobe’s Camera Raw editor continues to be updated so those formats can be read At least for now, you are probably covered

The even better news is that Adobe has introduced a camera raw format that they are trying to make an industry standard for camera raw—the DNG file Using Adobe’s DNG converter, you can

Part II: Working with Camera Raw Images

convert your camera raw files (whatever format they are currently) to DNG files Adobe’s been around a long time, and DNG is not proprietary I’m willing to bet on them

I’ll talk a little more about DNG files later in this chapter when I discuss camera raw file types

Memory card and disk space

Another downside, at least for now, of camera raw formats is their sheer size At over twice the size

of their largest JPEG counterparts, they can fill up memory cards and even hard disks at an aston-ishing rate Even as memory cards and disks become bigger, so does the megapixel capability of cameras If you take lots of pictures (and who doesn’t, in this digital age?), you’ll want to be sure that you have plenty of memory on hand to store them

Another consequence of having such big file sizes is that computer processing time is significantly increased—not only when you actually take the pictures, but also after those photos are imported into Bridge and Photoshop These files are harder for Bridge to manage because of their sheer size

Every change you make to them in Photoshop takes longer to process than it would in smaller files

The good news here is that Camera Raw handles these files really well The changes you make to your photos in Camera Raw happen in real time Processing in Camera Raw, especially after you get the hang of the application, doesn’t need to take more than a few seconds

Time

It’s not just computer processing time that is an issue; what about your own personal time? Doesn’t

it take lots of extra time to process all those camera raw images so they look good? If you are tak-ing hundreds or even thousands of shots in one photo shoot, isn’t it too much to ask that you would need to go back and process each of those images?

Actually, this is a misconception It doesn’t take more of your time to work with camera raw files;

it actually takes less Consider these facts:

l The camera raw files are already processed according to your camera settings and look just like the same shot taken with a JPEG setting If your camera settings were right on, great!

You don’t even need to open your photos in Camera Raw

l When you do open your photos in Camera Raw, processing them is simpler by far than using adjustments in Photoshop to clean your image With all the extra color information

at your fingertips, finding the right settings is simple

l You can batch process your raw images If you have taken several photos in the same lighting conditions, for instance, you can adjust the white balance on all of the photos at the same time

l If you aren’t using your photos in a composite or adding special effects to them, there’s no need to open them in Photoshop You can even save a JPEG copy (or one of several other file formats) right from Camera Raw With that taken into consideration, even the increased computer processing time doesn’t seem to weigh in as a huge time factor

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Camera Raw File Types

I’ve already explained that there are as many or more camera raw file types as there are camera brands that capture them Some of the more notable ones are Canon’s formats (CR2, CRW), Nikon’s formats (NEF, NRW), and Sony’s formats (ARW, SRF, SR2), just to name a few Your cam-era has its own format, and you should get to know the ins and outs of that particular format because no two are exactly alike If you have a newer or less common format, you may want to be sure you can open your files in Camera Raw You could look for supported formats, but the easiest way is just to try to open a photo in Camera Raw If it works, you’re good to go

Note

Adobe is constantly updating the supported raw formats If your files don’t open on the first try in Camera

Raw, make sure you’ve installed the latest updates n

XMP

When you change a supported file format using Camera Raw, those changes are saved as metadata

so your settings are permanent unless you want to change them The caveat is that even though Adobe can access many camera raw file formats, they are still proprietary, so Adobe can’t change

those files Adobe gets around this by creating a second sidecar file that contains the new metadata

This sidecar file has the extension XMP When you start to see these files floating around in your photograph folders, you’ll know what they are Don’t worry about them too much; they are called sidecar files for a reason They are connected to the camera raw file they interpret and move right along with it if you save it in a different location

DNG

No matter what raw format your camera supports, if Adobe supports it, you can convert your files

to DNG files

The DNG file extension stands for Digital Negative, and it is Adobe’s own camera raw format

Many proponents are fighting for it to become an industry standard This would alleviate the fear

of losing your valuable image data in the future as camera raw formats are dropped and no support

is available for them in new software applications

You can convert your camera raw files into DNG files by downloading the DNG converter from Adobe’s Web site (www.Adobe.com) It’s free and simple to use It takes a bit of time to run, so plan on walking away from your computer while it processes your files

Tip

Bridge also converts your raw files to DNG files while they are being imported from your camera or card

reader Choose Bridge as the method of importing these files and check Convert to DNG in the dialog n

There are two excellent reasons to convert your camera raw files into DNGs and one drawback