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Image Processing - A Matlab approach
BECDEC 701 – Image Processing
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The imshow function
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The imshow function
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The imshow function
imshow – expects the values between 0 and 1
for a matrix of type double
But here, cd has the values between 0 to 255.
A value less than 0 displayed as 0 (black)
A value greater than 1displayed as 1(white)
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The imshow function
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The imshow function
To display the matrix cd (double data type), we
need to scale it to the range 0 –
1.
This is easily done simple by dividing all values
by 255.
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The imshow function
Dividing by 512 darkens the image all
matrix values are now between 0 and 0.5.
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The imshow function
Dividing by 128 the range is 0 – 2, and all
pixels in the range 1 –
2 will be displayed as
white.
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The imshow function
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The imshow function
Remember,
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Quiz
What is the output image of the following code?
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Quiz - Answer
What is the output image of the following code?
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Quiz - Answer
What is the output image of the following code?
0 black
1 almost black
(a very dark grey)
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The im2double function
Convert the original image to double more
properly.
This applies correct scaling so that the output
values are between 0 and 1.
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The im2double function
produce a correct image
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double and im2double - conclusion
double changes the data type but does notchange the numeric values.
im2double changes both the numeric data type
and the values.
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im2int8
Corresponding to the functions double andim2double are the
uint8
im2uint8
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Binary Images
Binary image will have only two values: 0 and 1.
Matlab does not have a binary data type as such,
but it does have a logical flag, where uint8
values as 0 and 1 can be interpreted as logical
data.
The logical flag will be set by the use of
relational operations such as ==, < or > or any
other operations which provide a yes/no answer.
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Binary Images
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Binary Images
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Binary Images
Remove the logical flag from c1: done by
Logical flag is removed, but still hold the value
0 and 1 (double-data type).
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Binary Images
Logical flag is removed, but still hold the value0 and 1(double-data type).
binary data !!
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Binary Images
Turn the logical flag back on, and view theresult.
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Bit planes
Greyscale image can be transformed into asequence of binary images by breaking them
up into their bit-planes .
If we consider the grey value of each pixel ofan 8-bit image as an 8-bit binary word, then the
0th bit-plane consists of the last bit of each grey
value. (least signif icant bit plane )
7th bit most signi f icant bit plane
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Bit planes
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Bit planes – LSB plane
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Bit planes – LSB plane
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Bit planes – 1st bit plane
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Bit planes – 1st bit plane
156 1001 1100 159 1001 1111
158 1001 1110
160 1010 0000
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Method to find the Bit
Let pixels havevalues in the
range 0 to 7 000 0
001 1
010 2
011 3
100
4 101 5
110 6
111 7
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Bit planes – 2nd & 3rd bit planes
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Bit planes – 4th & 5th bit planes
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Bit planes – 6th & 7th (MSB) bit planes
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Most Significant Bit plane
The MSB plane, c7, is actually a thresholdof the image at level 127.
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Spatial Resolution
Spatial resolution is the density of pixels overthe image: the greater the spatial resolution,
the more pixels are used to display the image.
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Spatial Resolution
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Spatial Resolution
The effective resolution is 128x128
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Spatial Resolution
The effective resolution 64x64 & 32x32
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Spatial Resolution
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Spatial Resolution
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Spatial Resolution
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Point Processing
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Point Processing
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Remember
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Point Processing
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Point Processing
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Point Processing - Quiz
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Point Processing
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Point Processing
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Point Processing
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Point Processing
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Point Processing - Arithmetic Operations
i i i h i i
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Point Processing - Arithmetic Operations
i i A i h i O i
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Point Processing - Arithmetic Operations
P i P i A i h i O i
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Point Processing - Arithmetic Operations
P i P i A i h i O i
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Point Processing - Arithmetic Operations