read image-file
[image,colormap]=eimgread(imageFileName)
imageFileName :
name of JPEG- or PPM-file
image :
image matrix
if colormap used then
image is filled with indices of colormap
else
image is filled with RGB values
(value=R*2^16+G*2^8+B and R,G,B are integer of 0:255)
that’s a very fast way
colormap :
color table