Image File Types

Lak34635_02.qxd 11/5/02 5:20 PM Page 13 ESTIMATED TIME Image File Types HOURS SOURCE: ©PHOTODISC Objectives INTRODUCTION ● You will become familiar Whether a finished project is in a visual or with terms related to image file types. printed format, its impact is only as good as the image it pro- ● You will understand the duces. Many factors go into determining how best to produce difference between painting the image you need. In this chapter, you will explore some of and drawing programs. these factors and learn to make decisions that will help you in ● You will understand the selecting the best possible image format for your projects. difference among file types. This knowledge is essential for Amelia Sandefer, who must be ● You will identify able to make file format decisions in her job as an insurance advantages and investigator. She visits homes that have been damaged or disadvantages of file destroyed by accidents and uses a digital camera to record types. what she finds. She must also create simple drawings of her findings to attach to her reports for others to read. Since she only has a modem rather than a high-speed Internet connec- tion, she must keep her file sizes small to speed transmission. Chapter 2: Image File Types 13 Lak34635_02.qxd 11/5/02 5:20 PM Page 14 Figure 2.1 Bitmap images are the most Figure 2.2 Vector images are smoother common file format used in image than bitmaps and print without jagged management. edges. A pixel (picture element) is a data representation of a specific color at a specific PAINTING VERSUS DRAWING location in a matrix or grid. A rectangular collection of pixels Many software programs are available for creating and managing can produce an image on a images. Programs often used by businesses are Microsoft Paint, computer screen or on a Adobe Photoshop, Macromedia Fireworks, Jasc Paint Shop Pro, printed page. Adobe Illustrator, and Macromedia FreeHand. Image management programs are of two types: painting and drawing. Paint programs create images by using pixels (picture elements). Pixels are small squares (usually) with each pixel assigned a color (see Figure 2.1). Drawing programs create images by using mathemati- cally defined lines and curves that are treated as individual objects within the images (see Figure 2.2). Although paint programs are often easier to use, drawing programs give higher-quality results. Some image management programs such as Photoshop and Paint Shop Pro combine both painting and drawing options within a single program. IMAGE FORMATS OR FILE TYPES THE ETHICS OF GIF LICENSE Image programs save graphics with specific extensions indicat- In 1994, CompuServe Inc., and Unisys Corporation, the developers ing the file format. The extension of the GIF file format, announced their intention to require that all is shown by two to four letters commercial software companies using GIF compression in their following the dot in the name of programs pay licensing fees. This announcement caused a a file. For example, if a document considerable stir and resulted in the development of PNG file is named picture.jpg, “picture” is formats that were royalty-free. The average business user is the name of the file and “.jpg” is unaware that a licensing fee is required because it is paid by the the extension indicating the file software company. It is a good reminder, however, that not only format. are software programs protected by copyright but so are the You may not be able to see the products created using those programs. extension name unless you have 14 Unit 1: Image Management Procedures Lak34635_02.qxd 11/5/02 5:20 PM Page 15 enabled this option in the Folder View. Go to My Computer and open the C: drive. Choose View/Tools (depending on your operating system), Folder Options and click the View tab Ͼ as shown in Figure 2.3. Remove the check from Hide file extensions for known file types check box. (It is also possible to show or hide file extensions in Mac OS X.) Each image management program has a file format specific to that program, called its native or default format. For instance, Paint Shop Native refers to the file format Pro automatically saves images as .psp. Adobe Photoshop saves in which a particular graphics images as .psd. Generally, an image should be saved in its original program automatically saves or native format to use as an archive or backup of that image. By an image. doing this, you can open, edit, and then save the image in a different format without losing any quality. This is an important step in the creation of an image. Once a copy of the image has been saved in its native format, you can change to another file format by using the drop-down arrow next to the Format or Save as type box, as shown in Figure 2.4. From the list that appears, you can then choose the appropriate file format. Different file formats are appropriate for different situations, so it is important to understand the distinctions between the various file formats. For example, some programs can only import graphics with specific file formats. Some images look better saved as one format over another, and some images need to be small in order to load quickly on the Internet. Knowledge of file formats enables you to make the best choice. SOURCE: ©MICROSOFT WINDOWS 98 SOURCE: ©MICROSOFT WINDOWS 98 Figure 2.3 To see extensions, click on the radio button Figure 2.4 Once an image has been saved in native format, box indicated by the arrow. choose Save as and click on the drop-down arrow to select another format. Chapter 2: Image File Types 15 Lak34635_02.qxd 11/5/02 5:20 PM Page 16 PAINTING PROGRAMS Painting programs (or paint programs) create bitmap images made of pixels. Each pixel has a defined color, size, and place in the image. The sharpness of the image is determined by the density of the pixels, and this density determines the resolution. Resolution is defined as A bitmap is a graphic created dots per inch (dpi) or by the numbers of pixels in rows and columns by using pixels. (640 ϫ 480). The higher the resolution, the better your image will Resolution is the density of appear or print out but the larger the file will be. pixels in an image. Amelia has learned that sometimes it is important to save her digital images in the highest possible resolution if she knows that others will want to print a large color version. She also knows that often all that is necessary is an image that can be printed on a black-and-white laser printer. For example, recently she needed an overall picture of a home that had been hit by a careless driver. She knew that a quick low-resolution shot of the damaged brick wall would serve her pur- pose. At the same time, though, she needed a detailed picture of the interior damage. One of the most common types of bitmapped images is a BMP (Bitmap) file. A BMP image is usually used in word processing documents. BMP file sizes are often quite large, even though they are usually limited to 256 colors because they are not compressed as some other formats are. BMP files work well in programs that require the Microsoft Windows operating system. A bitmap file type that works well in all environments is TIF or TIFF (Tagged Image File Format). Like BMP files, these files are quite large and are often used in print documents. TIFF files are not compressed and can show 16 million colors. Many scanners produce images as TIFF files, and some digital cameras can save photographs in TIFF format as well. The file formats most often used for Web pages are GIF (Graphics Interchange Format) and JPG or JPEG (Joint Photographic Experts Group). GIF, pronounced with either a hard or soft “G,” is an image file format developed by CompuServe. Because GIFs use only 256 colors, the file sizes are quite small. GIFs are used to create line draw- Compression in graphic files is ings, images with transparent backgrounds, and animated figures. the process of reducing the size Because photographs require greater color depth, they lose much of of the image. their quality if they are saved as GIFs. Lossless compression does not The time it takes to download a graphic on the Internet depends on change any pixel data. the size of the file. To improve download speed, several algorithms Lossy compression reduces the (sequences of steps to perform a function) have been written to size of a file by removing pixels reduce or compress the size of the file. The two types of compression that are not essential. are lossless and lossy. Lossless compression reduces the file size with- Interlacing displays an image out losing any pixel information. Lossy compression changes some on a Web page in stages until pixels while making the file size smaller. The main drawback of a the image has reached its full lossy algorithm is that the greater the compression, the poorer the resolution. quality of the image. In business image management, it becomes Noninterlacing renders an important to balance quality with file size. image from top to bottom until GIF compression is lossless using the LZW (Lempel-Ziv-Welch) for- the image is complete. mula, named for the developers. The two versions are 87a and 89a. Most users find 89a to be the best choice because it allows transparency.

Load more