Developing with PDF

Chapter 3. Images

In the previous chapter you learned how to create vector graphics, a series of lines and paths (and sometimes text) that have no predefined resolution and can be composed of multiple colorspaces and attributes. However, in many cases you may need to utilize a raster image (sometimes called a bitmap image) on your page. This chapter introduces them to you.

Raster Images

When most people think about raster images, they think about standard raster image formats such as JPEG, PNG, GIF, or TIFF. And while those formats do contain raster image data, they also contain all sorts of other things in a form of “image package.” For PDF, however, you can’t use the full package (except in one special case—see JPEG Images), and you need to “unwrap” it to get at the raw form that PDF expects.

This “raw form” is just a series of pixels, or in more technical terms, a two-dimensional array of those pixels (the two dimensions being the height of the image and the width of the image). For example, in Figure 3-1, the height is 40 pixels and the width is 46 pixels.

Figure 3-1. Large pixel (FatBits) image

Each of the pixels in that image, as mentioned previously, is really itself an array of values—one per number of colors (also known as color components) in the color space. If this were a DeviceRGB image, then each pixel would have three elements. However, if it were a DeviceCMYK image, there ...