Computer graphics professionals use programs that support high resolutions to have more control over the display of bitmap images.
With some programs, such as IrfanView ( you can view many types of images with other programs, you can view or work with only the graphics files they create.
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Software includes drivers, which are coded instructions that set a video card s display parameters, and programs used to create, modify, and view images. Software also contributes to image quality. Because a bitmap image is defined by pixel size, high-resolution images use smaller pixels than low-resolution images do.
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For example, the monitor and video card on your Windows computer might support a resolution, which means displaying 1024 pixels horizontally and 768 pixels vertically.ģ Recognizing a Graphics File 383 The more pixels displayed, the smaller they must be to fit onscreen and, therefore, the smaller pictures appear onscreen. The more advanced the video card s electronics and the more memory it has, the more detailed instructions it can accept, resulting in higher-quality images. Computers also use a video card containing a certain amount of memory for displaying images. Monitors can display a range of resolutions the higher the resolution, the sharper the image. Resolution is related to the density of pixels onscreen and depends on a combination of hardware and software. A bitmap s image quality on a monitor is governed by resolution, which determines the amount of detail that s displayed. In most cases, printing an image converts, or rasterizes, it to print pixels line by line instead of processing the complete collection of pixels. Raster images are also collections of pixels, but they store pixels in rows to make images easy to print. Understanding Bitmap and Raster Images Bitmap images store graphics information as grids of pixels, short for picture elements. However, converting graphics files in this way can change the image quality, as you see in a Hands-On Project at the end of this chapter. If you open a graphics file in a graphics editor that supports multiple file formats, you can save the file in another file format. Each format has different qualities, including the amount of color and compression it uses. When you use a graphics editor or an image viewer, you can open a file in one of many graphics file formats, such as.bmp.gif, or.eps. You use image viewers to open and view graphics files but not change their contents. You use graphics editors to create, modify, and save bitmap, vector, and metafile graphics. You can use two types of programs to work with graphics files: graphics editors and image viewers. Metafile graphics are combinations of bitmap and vector images.
Vector graphics are based on mathematical instructions that define lines, curves, text, ovals, and other geometric shapes. Bitmap images are collections of dots, or pixels, in a grid format that form a graphic. A graphics program creates one of three types of graphics files: bitmap, vector, and metafile. You might have used a graphics program, such as Microsoft Paint, Adobe Photoshop, or Gnome GIMP, to create or edit an image.
Recognizing a Graphics File Graphics files contain digital photographs, line art, three-dimensional images, and scanned replicas of printed pictures. Copyrights determine the ownership of media, such as images downloaded from a Web site. Steganography involves hiding data, including images, in files. This chapter also explores tools for viewing graphics files you recover and discusses two computer graphics issues: steganography and copyrights.
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You learn how to identify and reconstruct graphics file fragments, analyze graphics file headers, and repair damaged file headers. This chapter begins with an overview of computer graphics and data compression, and then explains how to locate and recover graphics files based on information stored in file headers. To examine and recover graphics files, you need to understand the basics of computer graphics, including file characteristics, common file formats, and compression methods for reducing file size. 1 chapter10 Recovering Graphics Files After reading this chapter and completing the exercises, you will be able to: Describe types of graphics file formats Explain types of data compression Explain how to locate and recover graphics files Describe how to identify unknown file formats Explain copyright issues with graphics 381Ģ 382 Chapter 10 Many computer forensics investigations involve graphics, especially those downloaded from the Web and circulated via.