Understanding the Image-Creation Process
Creating an image with PHP is not like creating an image with a drawing program: There's no pointing and clicking or dragging buckets of color into a predefined space to fill your image. Similarly, there's no Save As functionality, in which your drawing program automatically creates a GIF or JPEG or PNG (and so on) just because you ask it to do so.
Instead, you have to become the drawing application. As the programmer, you must tell the PHP engine what to do, at each step along the way. You are responsible for using the individual PHP functions to define colors, draw and fill shapes, size and resize the image, and save the image as a specific file type. It's not as difficult as it might seem, however, if you understand each step along the way and complete the tasks in order.
A Word About Color
When defining colors in your image-related scripts, you will be using the RGB color system. Using decimal values from 0 to 255 for each of the red, green, and blue (R, G, and B) entries, you can define a specific color. A value of 0 indicates no amount of that specific color, while a value of 255 indicates the highest amount of that color.
For example, the RGB value for pure red is (255,0,0) or the entire allocation of red values, no green, and no blue. Similarly, pure green has a value of (0,255,0), and pure blue has a value of (0,0,255). White, on the other hand, has an RGB value of (255,255,255), while black has an RGB value of (0,0,0). A nice shade of purple has an RGB value of (153,51,153), and a light gray has an RGB value of (204,204,204).