Hello, Consider the following quote from this OpenGL ES for iOS Book:
And this quote:
My question is how does one determine how many texels are in an image and how large those texels are. If I'm not mistaken 1 texel != 1 pixel, so you can't determine the number of texels by counting pixels. For example, the second quote describes an image with alternation black and white texels. How would you know if your image is composed of black and white texels.... who defines the texel size??
Here's my understanding:
The term pixels means dots on the screen.
OpenGL uses the term "texels" to talk about dots in a source image (texture.) At display time, a texture gets mapped onto a 2D or 3D shape, and there is no longer a one-to-one mapping between texels and pixels.
Most of us think of pixels and texels interchangeably, but in OpenGL terms, they are not interchangeable.
A bitmap image is a grid of dots. The number of texels is simply image heightxwidth.
An image does not have a size, and so the dots on the image do not have a size. They're data. If you map the texture directly onto the screen, where 1 texel takes 1 pixel, then at that moment, each texel is displayed at the size of a screen pixel.
However, with OpenGL that's the exception rather than the rule. Usually you scale textures, wrap them around shapes, rotate them, skew them, etc, in ways that mean there is no single mapping from texel size to pixel size.
