Pro OpenGL ES for iOS

142 CHAPTER 5: Textures^

Figure 5-12. Stretching a texture across many faces

Image Formats

OpenGL ES supports many different image formats, and I’m not talking about PNG vs.

JPEG, but I mean the form and layout in memory. The standard is 32 bits, which assigns

8 bits of memory each for red, green, blue, and alpha. Referred to as RGBA, it is the

standard used for most of the exercises. It is also the ‘‘prettiest’’ because it provides

more than 16 million colors and translucency. However, you can often get away with 16-

bit or even 8-bit images. In doing that, you can save a lot of memory and crank up the

speed quite a bit, with careful selection of images. See Table 5-1 for some of the more

popular formats.

Table 5-1. Some of the More Popular Image Formats

Format Details

RGBA 8 bits per channel, including alpha.

RGB 8 bits per channel, no alpha.

ALPHA A single 8-bit channel used for stencils.

LUMINANCE A single 8-bit channel for grayscale images.

RGB565 16 bits total: 5 for red, 6 for green, and 5 for blue. The green is given a little more

color fidelity because the eye is more sensitive to that than to either red or blue.

RGBA4444 16 bits, 4 for each channel.

RGBA5551 5 bits per color channel, and 1 for alpha.