Question

Given a Int array, an Argb32 image, how can i load this into Eigen Matrixes the best way?

The goal is to create a small image processing library. And as the first part i want to convert from RGB to Gray scale.

Are there any way to load the int[] into 3 eigen matrixes wihthout any memory copying ?

(when refering to eigen, its the Linear Algebra Library).

Answer 1

Yes, using the Map<> class with an appropriate inner-stride, for example:

unsigned char* data = ...;
int w, h; // the width and height
typedef Map<Matrix<unsigned char,Dynamic,Dynamic>, 0, InnerStride<4> > Slide;
Slice red(data, w, h), green(data+1, w, h), blue(data+2, w, h);

Then you can start playing with them, e.g., construct a gray level floating point version:

MatrixXf gray = (red.cast<float>() * 11 + green.cast<float>() * 16 + blue.cast<float>() * 5)/(32.*255.);