Tài liệu Photoshop cs5 by Dayley part 8 doc

63 CHAPTER Image Basics IN THIS CHAPTER Understanding the file formats that Photoshop supports for images, video, and 3D objects Knowing the difference between raster and vector images Opening an image in another format Understanding the resizing algorithms Creating a border around an image Cropping and straightening images Removing a border from an image P hotoshop’s purpose is editing image files that have come from a vari- ety of sources. Photoshop supports a large number of file formats. The different file formats can be confusing, so this chapter spends a bit of time talking about each of the different file formats to help you under- stand some of the benefits and drawbacks of each one. In this chapter, you also learn some other important concepts about file size and resolution. Understanding the relationship among the file size, the reso- lution, and the ultimate destination of the file helps you know what size and resolution to use for an image. You also learn the different types of algo- rithms that Photoshop uses to resample images when changing the size. Understanding the algorithms helps you know which ones to use to get the best results when resizing images. This chapter also discusses how and why to crop images. You learn how to use several tools in Photoshop to quickly and accurately crop, trim, rotate, and straighten images. Exploring File Types If you have worked with images long enough, you have probably come across a variety of file formats. Although having just one file format would be great, the fact is that numerous file formats serve a variety of purposes. You need to understand the different type of image, video, and 3D file formats to really make the most of Photoshop’s features. Understanding the different file formats helps you make better decisions about how to save and work with files. 07_584743-ch03.indd 6307_584743-ch03.indd 63 5/3/10 10:17 AM5/3/10 10:17 AM Part I: Getting Started with Adobe Photoshop CS5 64 This following sections focus on helping you understand the different types of file formats, where they came from, and why to use them. After you understand these points, you can make better decisions on importing and saving files with Photoshop. Compressed versus uncompressed The first concept you need to understand about file formats is whether the format stores the file in a compressed or uncompressed form. Each has its advantages, which is why both exist. An uncompressed file stores the full image, video, or 3D data in the same format that it exists when the file is opened. The size of the file on disk is the same as the size of the file in memory. A com- pressed file stores the data by using complex algorithms that allow the file to be stored using less space on disk. When the file is reopened, the data on disk is uncompressed using an inverse algo- rithm and loaded into memory in its original state. The advantage of using uncompressed file formats is that you always retain the data. Also, uncom- pressed formats are faster to load and save because the computer does not need to compress or uncompress them. The advantage of using compressed file formats is that they take up much less room on disk. With lots of large images and especially with video, this becomes a big concern. Two types of compression algorithms are used: lossless compression and lossy compression. The lossless compression algorithm loads the image back into memory in exactly the same state that it was before compression. However, the lossy compression algorithms “cheat” and throw away data that is not very relevant to displaying the image or video. Tip Lossy compression has a major advantage: Large images and video can be stored in a much smaller space. However, the major disadvantage is that every time you save an image using a lossy compression algorithm, you lose a bit of data. The first time you save, it probably doesn’t matter much. However, after several saves, you start seeing some artifacts in the image or video. To avoid this, use a lossless or uncompressed file type when you are editing the file; when you are finished editing it, save it in the lossy form for storage. Keep a copy of the original around if you need to edit the file again. n Raster versus vector Another file format concept that you need to understand is the difference between raster (or bit- map) and vector images. The data for an image is stored completely differently in these two file types. The image data is stored in raster images as a set of pixels in the image. Each pixel repre- sents one point of light in the image. The image is constructed onscreen by simply applying the pixel data in the image to a pixel on the screen. The data for a vector image is stored as a series of line data instead of individual pixels. Each line data item contains the length, direction, and color of the line. These lines make up the images. The image is constructed onscreen by using the line data to draw a series of lines. 07_584743-ch03.indd 6407_584743-ch03.indd 64 5/3/10 10:17 AM5/3/10 10:17 AM Chapter 3: Image Basics 65 The advantage of using vector images is that no matter how much you increase the size of the image, the lines are always crisp because they can be redrawn each time. The disadvantage is that you cannot paint, adjust, and morph them the same way that you can raster images. The advantage of using raster images is that for photos and other smooth images, generating enough lines to make the resolution good enough to view can be difficult, if not impossible. Pixels are a much closer representation of how monitors, printers, and even the human eye work. Most of the image file formats you use in Photoshop are raster images. Raster images are much bet- ter for storing image data and allow for much more detail to be captured. For the most part, you will use vector images only when working with 3D images, text, line shapes, and paths in Photoshop. HDR images High Dynamic Range (HDR) images are images comprised of a set of photographs taken at differ- ent exposures in a technique known as exposure bracketing. The exact same photo is taken multi- ple times using different ISO settings and f-stops to create a wide range of exposures for the same image. These photos can then be combined to create a HDR image with a much greater tonal range than is possible in a single photo. Photoshop provides some tools to create and adjust HDR images. In Chapter 6 we discuss using the Bridge tools to create an HDR image. In Chapter 13 we discuss some of the tools used to adjust HDR images. Image files Photoshop supports a variety of image file types. Most people tend to work with one or two types and leave the others alone. However, having a basic understanding of all file types helps you make better choices when you have to work with them. The following sections describe some image file types and advantages/disadvantages of them. Photoshop (*.PSD, *.PDD) Photoshop natively uses its own Photoshop PSD file format. This file format contains all the infor- mation relevant to working with the image within Photoshop. For example, all the layer data you have created when working with the image is stored in the PSD file. Use the PSD file format when working with the image in Photoshop. The work done in Photoshop to create adjustment layers and other changes usually represents lots of work. The PSD file is the only format that stores all your work so you can fine-tune your adjustments later. The Photoshop file format maintains the full image data, so you need not worry about saving it multiple times. Photoshop PSD files can store image data in 8 bits per channel, 16 bits per chan- nel, and 32 bits per channel. One disadvantage of the Photoshop file format is that it takes up a large amount of disk space compared with some of the other file formats. 07_584743-ch03.indd 6507_584743-ch03.indd 65 5/3/10 10:17 AM5/3/10 10:17 AM Part I: Getting Started with Adobe Photoshop CS5 66 TIFF (*.TIF;*.TIFF) TIFF (Tagged Image File Format) is the next best format to PSD when saving your files. TIFF images can be stored in 8 bits per channel, 16 bits per channel, and 32 bits per channel. Advantages of the TIFF file formats are that it stores the layers that you create in Photoshop and can store transparency in the form of an alpha channel (discussed later in this book). TIFF images are also fairly large comparatively, so you may not want to use this file format for most images you will be working with. Another disadvantage is that TIFF images are typically not supported in Web browsers, so you can’t add them to Web pages. JPEG (*.JPG;*.JPEG;*.JPE) The JPEG file format has become by far the most commonly used. The JPEG format provides very good image quality supporting 16.8 million colors, combined with one of the best compression algorithms. This makes JPEG images the best quality for the file size that you can get. Consequently, most cameras use the JPEG image format by default. JPEG images are read by almost every computer program and are easily incorporated into Web pages. They also take much less disk space than PSD and TIFF files because they are compressed. JPEG 2000 (*.JP2;*.JPX) The JPEG 2000 file format uses a different encoding and compression system that makes the com- pression lossless. In addition, the JPEG 2000 file format supports 16-bit color for a greater range of colors, grayscale images, and 8-bit transparency. Although JPEG 2000 files provide a number of advancements over JPEG, they are not as widely supported and so they are still not used as often. Adobe provides a plug-in for Photoshop that will allow you to read and save files in the JPEG 2000 format. Caution JPEG images use a lossy compression algorithm, which means the more you change and save them, the worse the quality of the image becomes. You should convert the JPEG images to either PSD or TIFF to edit them and then back to JPEG when you are finished making the changes. n CompuServ GIF (*.GIF) The GIF (Graphics Interchange Format) has been the main graphic file used in developing Web pages since the inception of the World Wide Web. The GIF format uses an 8-bit palette that is lim- ited to 256 colors. The 8-bit palette makes the GIF images very small and easily transferred across the Internet. This makes the GIF file format perfect for creating images such as buttons, links, icons, and so on that are displayed on Web pages. A cool advantage of the GIF file format is that it supports animation effects within the image. This allows you to create animated controls and icons for Web pages. The GIF file format is lossless, so there is no data loss when saving files. 07_584743-ch03.indd 6607_584743-ch03.indd 66 5/3/10 10:17 AM5/3/10 10:17 AM Chapter 3: Image Basics 67 PNG (*.PNG) The PNG (Portable Network Graphics) file format was designed to replace the GIF file format for use on the Internet. The PNG file format has an advantage over GIF in that it supports 16.7 million colors as opposed to GIF supporting 256. However, there are still some drawbacks to the PNG file format. Some Web browsers do not support it, and while others support it, they do not handle things such as transparency and gamma correctly. As browsers become more adept at handling the PNG format, it definitely will replace the GIF file format, but for now you should consider working with GIF for Web images unless you need the additional colors available in PNG. Bmp (*.BMP; *.RLE; *.DIB) The BMP file format was developed for graphics in the Windows operating system. It is a simple format that is widely accepted by Windows applications. BMP files are not compressed, which makes them large. Another disadvantage is that there is not as much support outside of Windows—on Macs or Linux operating systems, for example. RAW (*.RAW; *.CR; *.CR2; *.DNG; and several others) The RAW image format was designed to capture the basic information collected by the CMOS sen- sors in digital cameras. Collecting the information directly without converting it to another file for- mat makes the cameras work faster and results in less data loss. Note The Open file dialog box in Photoshop provides options for Camera Raw and Photoshop RAW. Photoshop RAW are images that are saved in the RAW file format from Photoshop. The Camera Raw options are for files that are saved in a RAW file format by the camera. There are many different file extensions for the Camera Raw option because most camera venders have their own proprietary format. n The biggest advantage to using the RAW file format is that you can work with the image as close as possible to the state that existed when the photo was taken. Photoshop has designed as special tool, Adobe Camera Raw, discussed in Chapter 7, specifically for editing photos in the RAW state because the results tend to be much better than in other file formats. Tip If you are taking photographs that you really want to look good, you should set your camera to the RAW set- ting and use Adobe’s Camera Raw tools to adjust them. After they are adjusted, you can save them in another format, but if you may want to adjust them again, keep the Camera Raw files around. n One downside to the RAW file formats is that they have little support outside of image editors such as Photoshop. Another downside is that it is not one single format. In addition to the original . RAW file format, other vendors have added their own file formats. Canon has .CR and .CR2. Adobe has .DNG (Digital Negative), which is designed to try to standardize on a single format. 07_584743-ch03.indd 6707_584743-ch03.indd 67 5/3/10 10:17 AM5/3/10 10:17 AM Part I: Getting Started with Adobe Photoshop CS5 68 So far, the DNG format seems to be getting the best attention and support by hardware and soft- ware manufacturers. Portable bitmap (*.PBM;*.PGM;*.PPM;*.PNM;*.PFM;*.PAM) The PBM (Portable Bitmap), PGM (Portable Graymap), and PPM (Portable Pixmap) are basic file standards. They are so basic that they serve as one of the best common denominators for transfer- ring files between different platforms, going from Windows to Linux, for example. The other file formats tend to change files slightly when they are transferred between two different operating systems, due to differences in how the operating systems crunch numbers. Using these formats, you can overcome those problems more easily. Another advantage of the PBM file format is that it is one of the few formats that can store image data in 8 bit/channel, 16 bit/channel, and 32 bit/channel formats. This is another major advantage when trying to make an image portable from one system to another. Wireless bitmap (*.WBM;*.WBMPI) The WBM file format is designed for images used on wireless devices. Wireless devices are limited in the size and number of colors an image can contain. Using the Wireless bitmap format allows you to create images that can be displayed on most portable devices. Encapsulated PostScript (*.EPS; *.AI3-*.AI8; *.PS; *.EPSP; *.EPSF) The EPS (Encapsulated PostScript) file format was developed by Adobe as a means to store images in a format the PostScript printers can understand. That way, the file could be copied directly to the printer without the need to interact with the applications. Later, Adobe realized that this was an excellent means to transfer documents between different programs. Because all Adobe programs understand how to generate and read the EPS files, it was easy for one application to read an EPS file that was generated by another program. The greatest strength of the EPS file format is that it can contain both raster and vector images. This gives you the ability to generate a vector image in another program, in Adobe Illustrator, for example, and then import it into Photoshop. The vector image can then be used by Photoshop as a vector path, for instance. A major advantage of the EPS format is that its files are readable by almost every desktop layout program in use. One disadvantage is that it is not truly a graphic format. The EPS format is defi- nitely not the best format in which to store photos for later editing. Another disadvantage is that the EPS format results in a very large file because the storage format is not efficient. Photoshop PDF (*.PDF;*.PDP) The PDF file format was developed by Adobe to be a standard format for files that contained both vector and raster images. It has been widely accepted as a standard file format across all operating systems. 07_584743-ch03.indd 6807_584743-ch03.indd 68 5/3/10 10:17 AM5/3/10 10:17 AM Chapter 3: Image Basics 69 PDF files can be read by many applications including Photoshop. When Photoshop opens a PDF file, it allows you to import the pages and images separately, as shown in Figure 3.1. FIGURE 3.1 Selecting to import pages and images when opening a PDF file in Photoshop The biggest advantage to the PDF file format is how widely it has been adopted. It is the de facto standard in publishing documents on the Internet, so it can be read everywhere. You will not use the PDF file format much in Photoshop, but it’s great when you need it. PCX (*.PCX) The PCX (Personal Computer eXchange) format was developed for use with the PC Paintbrush utility for DOS. If you don’t know what DOS is, don’t worry; it’s best forgotten. The PCX format was widely used several years ago, but it has lost pace and been replaced with the GIF, JPEG, and PNG file formats. You probably don’t need to use the PCX file format unless you are using an image that was created several years ago. Keep in mind that PCX files originally had a maximum of 256 colors, so don’t expect PCX files to contain much detail. PICT (*.PCT;*.PICT) PICT files are sort of the Apple version of PCX files. The PICT file format was original developed for use with the QuickDraw utility. The format was one of the few at the time that allowed a file to contain both vector and raster images. However, that functionality has been replaced by the EPS and PDF file formats. 07_584743-ch03.indd 6907_584743-ch03.indd 69 5/3/10 10:17 AM5/3/10 10:17 AM Part I: Getting Started with Adobe Photoshop CS5 70 Pixar (*.PXR) The Pixar file format is a format developed in-house by the Pixar animation company. The require- ments of digital animation put such as huge strain on the available applications that they had to create a custom system including their own file format. Photoshop allows you to read images that were created using Pixar’s system and to write your images out to the Pixar file format. It’s probably not useful to most people, but handy when it is necessary. FXG (*.FXG) FXG (Flash XML Graphics) is an .XML graphics file format developed by Adobe. The specific pur- pose of the FXG file format is to provide a common file format for all Adobe products. The FXG file format is based on the XML language and defines a standard for raster graphics. This is still a developing file format that has lots of potential. Google Earth 4 (*.KMZ) A KMZ file is a zipped archive used by the Google Earth application to display geographic data and images. A KMZ file contains one or more KML files and the supporting images. Google Earth uses the KML files similarly to how a Web browser uses HTML files. The Google Earth application reads the KML file and interprets how to display the information and images. Photoshop allows you to read a KMZ file and open the images it contains to edit and view. Currently, Photoshop supports KMZ files using the Google Earth 4 standard only. PSB (*.PSB) Many applications have a basic limit of 2GB for a file size due to the nature of the 32-bit operating system. This presents a problem for many file formats. Systems have overcome this by using a spe- cial file called PSB (large document format). Using the PSB file format, Photoshop can open and create files that are larger than 2GB. An advan- tage of the PSB file format is support for the 8 bit/channel, 16 bit/channel, and 32 bit/channel for- mats. However, unless you really need a file larger than 2GB, avoid using the PSB format. Only a few applications support it, so it is not very portable. Another disadvantage of the PSB file format is that you can use only the grayscale and RGB color models, which are discussed in Chapter 4. OpenEXR (*.EXR) The OpenEXR format was developed by Industrial Light and Magic to provide a multi-resolution and arbitrary channel format for images. This can be a major advantage if you are working with complex compositing of images where you may need several different channels that do not con- form to a single color mode. Although Photoshop gives you the ability to read and even write an OpenEXR file, it does not allow you to create the additional channels. However, if you have an OpenEXR file, you can use Photoshop’s powerful tools to make adjustments to the channels. 07_584743-ch03.indd 7007_584743-ch03.indd 70 5/3/10 10:17 AM5/3/10 10:17 AM Chapter 3: Image Basics 71 Cineon The Cineon file format was developed by Kodak to contain data from images scanned in from film. The Cineon format is a bit different from the standard formats such as JPEG and TIFF. Instead of RGB channels representing intensity of color, the pixel data in the Cineon format represents the printing density as seen by the print film. The purpose of using the printing density is to retain the values that originally existed on the print film. IFF (*.IFF;*.TDI) The IFF (Interchange File Format) was developed by Electronic Arts as a method to transfer graphic data between software. It is unlikely that you will come across the need to use an IFF, but if you do, Photoshop can open it. Scitex CT (*.SCT) The Scitex CT file format is used by Scitex Corporation Ltd. graphics processing equipment. This file format is usually used only if you are sending print jobs to a Scitex digital printer. Targa (*.TGA; *.VDA; *.ICB; *.VST) The Targa (Truevision Advanced Raster Graphics Adapter) file format has been around since the birth of color displays in computers. Targa files support 8, 16, 24, and 32-bit colors per pixel. Targa files support alpha channel data and are fairly transportable between systems. A common use of Targa files is to store textures used in 3D imaging such as video games or animation. Radiance (*.HDR; *.RGBE; *.XYZE) The Radiance format stores four bytes per pixel (red, green, blue, and an exponent byte). This allows pixels to have the extended range and precision similar to floating point values allowing the HDR and RBGE formats to handle very bright pixels without loss of precision for darker ones. A variant of the Radiance format, XYZE, uses the XYZ color model (discussed in Chapter 29) instead of RGB. Video files With the addition of the Timeline palette, Photoshop adds several video file formats to the huge list of supported file formats. Not only can you import movies with the following extensions, you can import image sequences with the usual image extensions that Photoshop already supports. Photoshop allows you to import the following video file formats: l MOV: The MOV file format is the native file format of QuickTime. A .MOV file can con- tain several types of tracks—video, audio, effects, and text among them. This makes them easily editable and portable because a .MOV file can be used in both the Macintosh and Windows platforms. l AVI: AVI is the highest quality file format available because it usually isn’t compressed, although some AVI codes compress the video file. This means that it takes up much more 07_584743-ch03.indd 7107_584743-ch03.indd 71 5/3/10 10:17 AM5/3/10 10:17 AM . systems. 07_ 584 743-ch03.indd 680 7_ 584 743-ch03.indd 68 5/3/10 10:17 AM5/3/10 10:17 AM Chapter 3: Image Basics 69 PDF files can be read by many applications including Photoshop. When Photoshop opens. standardize on a single format. 07_ 584 743-ch03.indd 6707_ 584 743-ch03.indd 67 5/3/10 10:17 AM5/3/10 10:17 AM Part I: Getting Started with Adobe Photoshop CS5 68 So far, the DNG format seems to be. has been replaced by the EPS and PDF file formats. 07_ 584 743-ch03.indd 6907_ 584 743-ch03.indd 69 5/3/10 10:17 AM5/3/10 10:17 AM Part I: Getting Started with Adobe Photoshop CS5 70 Pixar (*.PXR) The