replace RGB values with new values

How to change the pixel values of a RGB image to

% if pixel value is in the following range
0-64  to 0 
65-128 to 1
129-192 to 2
192-255 to 3

How to change in all the channels without using for loop

Answer 1

[Dyuman Joshi]

rgb=[67,68,69;0,67,69;0,66,68;125,126,127;122,125,127;117,122,126;113,114,115;110,113,115;106,111,114]

rgb = 9×3

67 68 69 0 67 69 0 66 68 125 126 127 122 125 127 117 122 126 113 114 115 110 113 115 106 111 114

floor(abs(rgb-1)/64)

ans = 9×3

1 1 1 0 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

[DGM]

If the input is properly uint8 class, then the output won't be as expected. So long as the input is at least scaled [0 255], the following should work regardless of input class, and the output will be cast properly for the scale.

uint8(floor(abs(double(rgb)-1)/64))

[Elysi Cochin]

Thank you both of you. For uint8 @DGM comment should be considered.