Image File Types. Objectives. Whether a finished project is in a visual or INTRODUCTION

Transcription

1 ESTIMATED TIME Image File Types H O U R S SOURCE: PHOTODISC INTRODUCTION Whether a finished project is in a visual or printed format, its impact is only as good as the image it produces. Many factors go into determining how best to produce the image you need. In this chapter, you will explore some of these factors and learn to make decisions that will help you in selecting the best possible image format for your projects. This knowledge is essential for Amelia Sandefer, who must be able to make file format decisions in her job as an insurance investigator. She visits homes that have been damaged or destroyed by accidents and uses a digital camera to record 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 connection, she must keep her file sizes small to speed transmission. Objectives You will become familiar with terms related to image file types. You will understand the difference between painting and drawing programs. You will understand the difference among file types. You will identify advantages and disadvantages of file types. Chapter 2: Image File Types 13

2 Figure 2.1 Bitmap images are the most common file format used in image management. Figure 2.2 Vector images are smoother than bitmaps and print without jagged edges. A pixel (picture element) is a data representation of a specific color at a specific location in a matrix or grid. A rectangular collection of pixels can produce an image on a computer screen or on a printed page. PAINTING VERSUS DRAWING Many software programs are available for creating and managing images. Programs often used by businesses are Microsoft Paint, Adobe Photoshop, Macromedia Fireworks, Jasc Paint Shop Pro, 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 mathematically 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. THE ETHICS OF GIF LICENSE In 1994, CompuServe Inc., and Unisys Corporation, the developers of the GIF file format, announced their intention to require that all commercial software companies using GIF compression in their programs pay licensing fees. This announcement caused a considerable stir and resulted in the development of PNG file formats that were royalty-free. The average business user is unaware that a licensing fee is required because it is paid by the software company. It is a good reminder, however, that not only are software programs protected by copyright but so are the products created using those programs. IMAGE FORMATS OR FILE TYPES Image programs save graphics with specific extensions indicating the file format. The extension is shown by two to four letters following the dot in the name of a file. For example, if a document is named picture.jpg, picture is the name of the file and.jpg is the extension indicating the file format. You may not be able to see the extension name unless you have 14 Unit 1: Image Management Procedures

3 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 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 Pro automatically saves images as.psp. Adobe Photoshop saves images as.psd. Generally, an image should be saved in its original or native format to use as an archive or backup of that image. By 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. Native refers to the file format in which a particular graphics program automatically saves an image. SOURCE: MICROSOFT WINDOWS 98 Figure 2.3 To see extensions, click on the radio button box indicated by the arrow. SOURCE: MICROSOFT WINDOWS 98 Figure 2.4 Once an image has been saved in native format, choose Save as and click on the drop-down arrow to select another format. Chapter 2: Image File Types 15

4 PAINTING PROGRAMS A bitmap is a graphic created by using pixels. Resolution is the density of pixels in an image. Compression in graphic files is the process of reducing the size of the image. Lossless compression does not change any pixel data. Lossy compression reduces the size of a file by removing pixels that are not essential. Interlacing displays an image on a Web page in stages until the image has reached its full resolution. Noninterlacing renders an image from top to bottom until the image is complete. 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 dots per inch (dpi) or by the numbers of pixels in rows and columns ( ). The higher the resolution, the better your image will appear or print out but the larger the file will be. 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 purpose. 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 drawings, images with transparent backgrounds, and animated figures. Because photographs require greater color depth, they lose much of their quality if they are saved as GIFs. The time it takes to download a graphic on the Internet depends on the size of the file. To improve download speed, several algorithms (sequences of steps to perform a function) have been written to reduce or compress the size of the file. The two types of compression are lossless and lossy. Lossless compression reduces the file size without losing any pixel information. Lossy compression changes some pixels while making the file size smaller. The main drawback of a lossy algorithm is that the greater the compression, the poorer the quality of the image. In business image management, it becomes important to balance quality with file size. GIF compression is lossless using the LZW (Lempel-Ziv-Welch) formula, named for the developers. The two versions are 87a and 89a. Most users find 89a to be the best choice because it allows transparency. 16 Unit 1: Image Management Procedures

5 A second consideration when choosing a GIF is interlaced or noninterlaced. Interlaced images load onto a Web page in stages, with the first image appearing at a minimal resolution, so the viewer can begin to see part of the picture even before it is completely loaded. At intervals, the picture reloads until the maximum resolution is reached. Noninterlaced images build from the top down until a complete image appears. Interlacing slightly increases file size, so it should be limited to large images that take a long time to download. Both Photoshop and Paint Shop Pro provide version options and interlacing choices. JPG or JPEG (pronounced jay-peg ) is another file type. Using up to 16 million colors, JPG images reproduce the quality, color, and detail found in photographs or graphics using blends and gradients. Most digital cameras save photographs as JPGs to conserve memory space on the camera s storage device. The JPG compression formula allows you to choose the amount of compression you want, so you can decide at what point the image quality matches your needs. It also allows you to choose between standard and progressive encoding, much as with interlacing for GIFs. A third choice for use on the Internet is the PNG (Portable Network Graphics) format. It retains all 16 million colors and has some valuable features, but it is not supported by all Web browsers. Amelia has learned to save her images in TIFF format and then to convert them to the format that best serves her purpose. This way she knows that she can always return to the original and create a copy in a different format without losing quality. This came in quite handy last week when she was asked to submit a picture she had taken of a tornado-destroyed home. The corporate office wanted to use her picture in their publication and needed the highest quality possible. Her TIFF version met their needs and she was pleased to see her picture featured the following month. DRAWING PROGRAMS Drawing programs create images made of mathematically defined lines and curves, or vectors. An advantage of vector graphics over bitmap images is that regardless of how much the image is enlarged or reduced (called Job Search Skills The first step in finding the job that s right for you is to target specific jobs and careers. Decide what you want not just now but five or ten years into the future. Have a career plan. One way to know what you want is to try out a wide range of jobs through part-time work, volunteering, and so forth. Then research potential employers that can offer you the kind of job or career you seek. Perhaps the most important part of the job search involves simply talking with people. Tell everyone you meet you re in the job market; you might make an important contact. Develop a network of people who work in your field of interest. By critiquing your résumé and asking you questions about yourself and your goals, your contacts can help you sharpen your résumé and interviewing skills key components in a successful job search. Be sure to send acknowledgment letters to everyone you talk with; this builds your credibility and sends the message that you re a professional who is serious about your career. Above all, be persistent! Digging Deeper: Research some local multimediarelated companies and develop a list of people within the companies you might approach for a brief informational interview. Arrange and follow through with an interview. Discuss your impressions in class. Chapter 2: Image File Types 17

6 A vector is an image created by using a series of mathematically defined lines and curves rather than pixels, making the image easier to resize or scale. scaling), the quality remains the same. A vector graphic is smoother than a bitmap graphic because the image is mathematically derived for each output device. Once a vector graphic is completed, it can be converted to a bitmap image. (Another name for a bitmap is raster, so this process is called rasterizing.) Vector graphics are converted to bitmap images for use on the Internet. Shockwave Flash images and animations are vector graphics. Vector graphics are smaller in size than bitmaps, but they are limited because they cannot show gradations of colors as bitmaps can. The most common native vector file formats are CDR for Corel- Draw, AI for Adobe Illustrator, FH for Macromedia FreeHand, SWF for Shockwave Flash, and WMF for Windows Metafile. EPS (Encapsulated PostScript) is a general-purpose vector file format that has both the vector image data and a screen preview in the same file. It is most commonly used for printing purposes. Amelia finds drawing programs very helpful in her work. She uses a vector program to create sketches of the details that might be necessary to supplement her reports. She likes the fact that she can modify length and width of lines even after completing a drawing. In her last report, Amelia added a drawing showing the path of the automobile from the street to the wall of the home that was struck. She added details such as specific measurements and estimated speed of travel. These kinds of details have made her information well respected by her employer. SUMMARY In this chapter, you have learned about file formats and their purposes as shown in the chart below. Image file types can be divided into two groups: painting programs and drawing programs. Extensions for the most common painting file formats are.bmp,.tif,.gif,.jpg, and.png. Extensions for the file formats used for the Web are.gif,.jpg, and.png. Extensions for the most common drawing file formats are.cdr,.ai,.fh,.swf, and.wmf. The EPS file format, with the extension.eps, is a general-purpose vector file with a bitmapped preview. It is important that you understand the difference between file formats so that you can decide which ones will best meet your needs. File Acronym Type of Format Stands for Extension Program BMP Bitmap.bmp Painting TIFF or TIF Tagged Image File Format.tif Painting GIF Graphics Interchange Format.gif Painting JPG or JPEG Joint Photographic Experts Group.jpg Painting PNG Portable Network Graphics.png Painting PSD Photoshop Document.psd Painting JASC Jasc Paintshop Pro.psp Painting CDR CorelDraw.cdr Drawing AI Adobe Illustrator.ai Drawing FH Macromedia FreeHand.fh Drawing SWF Shockwave Flash.swf Drawing WMF Windows Metafile.wmf Drawing EPS Encapsulated PostScript.eps Drawing 18 Unit 1: Image Management Procedures

7 REVIEW Answer the following questions on your own computer. 1. What does a file extension look like? 2. What image management programs are often used by businesses? 3. What are the two types of image management programs, and how are they different? 4. What is a native format? 5. What is a bitmap image? 6. List four types of bitmap images. 7. Why are images compressed? 8. What is the difference between lossy and lossless compression? 9. What is an interlaced image? 10. Why might you want to use an interlaced image? 11. In what format do most digital cameras save images? 12. Why is the PNG format not used more often? 13. What is the advantage of using a vector graphic? 14. Name three native vector file formats and one general-purpose file format. 15. What company developed the GIF format, and what did the developer require beginning in 1994? DISCUSSION 1. Explain the difference between a vector and a bitmap. 2. Which file format is the most versatile? Why? 3. Why are photographs saved in JPEG format if they are to be used on the Internet? 4. Why is it important to understand file extensions? 5. Was CompuServe correct in its decision to charge a licensing fee? Why or why not? Chapter 2: Image File Types 19

8 USE YOUR KNOWLEDGE REVIEW 1. Use the table function in a word processing document to create a chart listing the advantages, disadvantages, and uses of all the file formats discussed in this chapter (see the chart that follows the summary). 2. Use a painting program to create a rectangle filled with color. Save the image in at least six different file formats (such as native, BMP, TIF, JPEG, GIF, and PNG). Look at the properties of each file and record, in the table you created in question 1, the size of each file. 3. Use a drawing program to create an image. The image should be a filled rectangle similar to the one created in step 2. Save the image in at least three different file formats (e.g., native, EPS). Look at the properties of each file and record in the table the size of each file. 4. Keeping in mind the advantages, disadvantages, and uses of each file format, choose one file format and write a slogan advertising the file format and its usefulness. Keep the slogan to eight words or fewer. FURTHER EXPLORATION 1. Survey your favorite Web sites (at least ten) to determine what file formats the sites are using for their images. To determine the type of file format, rightclick on the image and choose Save Picture As. The Save as type box will indicate the extension. 2. Create a chart showing the address of each site and the number of each type of image file used on each site. Observe and record which were interlaced and which were noninterlaced. 3. Do you disagree with the sites choices of file formats? How long did it take for pages to load? What can you suggest they do to increase the speed at which their pages appear? Write an explanation summarizing your comments. 20 Unit 1: Image Management Procedures