Raster Images

Written by Kevin Tavolaro
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Raster images are basic computer graphics files, frequently used in many applications. Bitmap (BMP) files are the common images among these files. Bitmaps are composed of square or rectangular pixels, which are tiny portions of an image file that define the graphic by providing color and shape to the file. Each is assigned a color and location within the file. The position and color of the pixels create the raster image as we see it, as the individual components all appear to be part of a single picture.

The amount of detail that a digital image can contain is determined by its resolution. A higher resolution means a more highly visible and legible image. Resolution is measured by the amount of pixels in an image. When a picture's resolution is presented, it is portrayed with two numbers. The first number indicates the width of the image, in pixels. The second number notes the height. Every pixel in an image file is creates one small dot. Hundreds of images arranged together can provide the details, color, and outline for a discernable picture, but lower image resolutions can provide nothing more than simple stick figures.

Converting Raster Images

While the amount of pixels in an image file defines its resolution, the overall quality of the image is related to the volume of data contained in each individual pixel. Pixels are measured by the amount of color information they can contain. This value, know as the pixel's "color depth," can range from four to 48 bits per pixel. Since the image quality is determined by the relationship resolution and color depth, you can't enhance the appearance of a raster image by enlarging it. Although resizing can make some aspects of a smaller raster image more apparent, the picture will lose quality, as its increased size diminishes the color depth, as well as increases the area covered by the same amount of pixels. One way to solidify the appearance of a raster image is to convert it into a PDF file. PDF documents are "resolution independent," which means they can show images clearly regardless of the resolution being used to view them, provided the images were properly embedded in the document when it was created.

PDF files were designed to appear the same on any system, allowing data to be exchanged between computer models and operating systems despite any differences. In addition to being system independent, PDF documents are also resolution independent, meaning their visibility remains consistent across platforms, regardless of each computer's individual resolution. This lets you be sure that any graphics in your document can be viewed clearly.


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