Image Processing Slides Nine

8/13/2019 Image Processing Slides Nine

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Image Processing - A Matlab approach

BECDEC 701 – Image Processing



2

The imshow function



3

The imshow function



4

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)



5

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.



7

The imshow function

Dividing by 512 darkens the image all

matrix values are now between 0 and 0.5.



8

The imshow function

Dividing by 128 the range is 0 – 2, and all

pixels in the range 1 –

2 will be displayed as

white.



9

The imshow function



10

The imshow function

Remember,



11

Quiz

What is the output image of the following code?



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Quiz - Answer




13

Quiz - Answer


0 black

1 almost black

(a very dark grey)



14

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.



15

The im2double function

produce a correct image



16

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.



17

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



20

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).



22

Binary Images

Logical flag is removed, but still hold the value0 and 1(double-data type).

binary data !!



23

Binary Images

Turn the logical flag back on, and view theresult.



24

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



31

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



32

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



35

Most Significant Bit plane

The MSB plane, c7, is actually a thresholdof the image at level 127.



36

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.



37

Spatial Resolution



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Spatial Resolution

The effective resolution is 128x128



39

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



44

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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i i A i h i O i



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P i P i A i h i O i



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P i P i A i h i O i




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Image Processing Slides Nine