I'm rather new to Matlab and am trying to convert a grayscale image into binary. The built in function im2bwI(I,level) only has one threshold that will make everything with a lower intensity value than the level black and everything higher white, but how can I make it so only values in a certain range become black? For example, how do I set it so pixels with intensity value 89 become black, but values 70 and 102 become white?
0
votes
2 Answers
2
votes
You can use logical addressing for this. I'll assume that 0 is black and 255 is white and you have your grayscale image in ImageMatrix. Please note that the values of white and black depend on the color depth (6 bit, 8 bit etc.) of the image.
Here's the code:
% Replace all values of 89 with 0 (black).
ImageMatrix(ImageMatrix == 89) = 0;
% Replace all values of 70 or 102 with 255 (white).
ImageMatrix(ImageMatrix == 70 | Imagematrix == 102) = 255;
For replacing a range of values from MinValue to MaxValue with NewValue:
% set some example values (replace values 192 ... 255 with 63):
MinValue = 192;
MaxValue = 255;
NewValue = 63;
ImageMatrix(ImageMatrix >= MinValue & ImageMatrix <= MaxValue) = NewValue;
0
votes
Answer: (let I be the image to be processed)
I(I == 89) = 0
I(I == 70 | I == 102) = 255
Real MATLAB test(R2012a) :
K>> I = ceil(rand( 12 ) * 34 + 69)
I =
98 94 101 74 102 80 78 86 78 100 101 74
100 103 102 100 72 101 99 98 88 96 101 87
74 74 83 88 94 94 84 100 87 100 86 88
96 90 85 91 99 84 94 96 70 81 77 85
73 95 91 71 78 84 72 99 98 89 93 103
88 71 83 97 90 71 76 93 100 81 99 89
101 81 86 75 88 88 72 90 87 80 94 89
99 73 86 99 86 74 101 102 81 70 75 77
95 100 78 92 92 70 81 91 90 89 85 74
93 86 95 88 70 92 86 83 100 77 82 71
79 84 87 95 83 97 89 87 82 98 82 85
80 93 92 84 100 89 85 85 97 87 79 99
K>> I == 89
ans =
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 1 0 0
0 0 0 0 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 1 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 1 0 0 0 0 0
0 0 0 0 0 1 0 0 0 0 0 0
K>> I == 70
ans =
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 1 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 1 0 0
0 0 0 0 0 1 0 0 0 0 0 0
0 0 0 0 1 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
K>> I == 102
ans =
0 0 0 0 1 0 0 0 0 0 0 0
0 0 1 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 1 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
K>> I(I == 89) = 0
I =
98 94 101 74 102 80 78 86 78 100 101 74
100 103 102 100 72 101 99 98 88 96 101 87
74 74 83 88 94 94 84 100 87 100 86 88
96 90 85 91 99 84 94 96 70 81 77 85
73 95 91 71 78 84 72 99 98 0 93 103
88 71 83 97 90 71 76 93 100 81 99 0
101 81 86 75 88 88 72 90 87 80 94 0
99 73 86 99 86 74 101 102 81 70 75 77
95 100 78 92 92 70 81 91 90 0 85 74
93 86 95 88 70 92 86 83 100 77 82 71
79 84 87 95 83 97 0 87 82 98 82 85
80 93 92 84 100 0 85 85 97 87 79 99
K>> I(I == 70 | I == 102) = 255
I =
98 94 101 74 255 80 78 86 78 100 101 74
100 103 255 100 72 101 99 98 88 96 101 87
74 74 83 88 94 94 84 100 87 100 86 88
96 90 85 91 99 84 94 96 255 81 77 85
73 95 91 71 78 84 72 99 98 0 93 103
88 71 83 97 90 71 76 93 100 81 99 0
101 81 86 75 88 88 72 90 87 80 94 0
99 73 86 99 86 74 101 255 81 255 75 77
95 100 78 92 92 255 81 91 90 0 85 74
93 86 95 88 255 92 86 83 100 77 82 71
79 84 87 95 83 97 0 87 82 98 82 85
80 93 92 84 100 0 85 85 97 87 79 99
