1. Vision system
(image processing)
By: karim ahmed abuamu
2. Image Representation
A digital image is a representation of a two-dimensional image as
a finite set of digital values, called picture elements or pixels
The image is stored in computer memory as 2D array of integers
Digital images can be created by a variety of input devices and
techniques:
digital cameras,
scanners,
coordinate measuring machines etc.
4. Types of Images
Digital images can be classified according to number and nature
of those samples
Binary
Grayscale
Color
5. Binary Images
A binary image is a digital image that has only two possible
values for each pixel
Binary images are also called bi-level or two-level
Binary images often arise in digital image processing as masks or
as the result of certain operations such as segmentation,
thresholding.
7. Grayscale Images
A grayscale digital image is an image in which the value of each
pixel is a single sample.
Displayed images of this sort are typically composed of shades of
gray, varying from black at the weakest intensity to white at the
strongest.
The values of intensity image ranges from 0 to 255.
9. True color images
A true color image is stored as an m-by-n-by-3 data array that
defines red, green, and blue color components for each individual
pixel.
The RGB color space is commonly used in computer displays
11. Image segmentation
In computer vision, image segmentation is the process of partitioning a
digital image into multiple segments (sets of pixels, also known as superpixels).
The goal of segmentation is to simplify and/or change the representation of an image
into something that is more meaningful and easier to analyze.
Image segmentation is typically used to locate objects and boundaries (lines, curves,
etc.) in images. More precisely, image segmentation is the process of assigning a
label to every pixel in an image such that pixels with the same label share certain
visual characteristics.
12. Histograms
o A tool that is used often in image analysis .
o The (intensity or brightness) histogram shows how many
times a particular grey level appears in an image.
o For example, 0 - black, 255 – white.
7
0 1 1 2 4 6
5
2 1 0 0 2 4
3
5 2 0 0 4 2
1
1 1 2 4 1 0
0 1 2 3 4 5 6
image histogram
13. Histogram Features
An image has low contrast when the complete range of possible
values is not used. Inspection of the histogram shows this
lack of contrast.
23. Thresholding (image processing)
Threshold converts each pixel into black, white or unchanged depending on
whether the original color value is within the threshold range.
Thresholding is usually the first step in any segmentation
Single value thresholding can be given mathematically as follows:
1 if f ( x, y ) > T
g ( x, y ) =
0 if f ( x, y ) ≤ T
24. Imagine a poker playing robot that needs to visually interpret the cards in
its hand
Original Image Thresholded Image
25. If you get the threshold wrong the results can be disastrous
Threshold Too Low Threshold Too High
26. Basic Global Thresholding
Based on the histogram of an image Partition the image histogram using a
single global threshold
The success of this technique very strongly depends on how well the histogram
can be partitioned
The basic global threshold, T, is calculated as follows:
1. Select an initial estimate for T (typically the average grey level in the
image)
2. Segment the image using T to produce two groups of pixels: G1
consisting of pixels with grey levels >T and G2 consisting pixels with grey
levels ≤ T
3. Compute the average grey levels of pixels in G1 to give μ1 and G2 to give
μ2
27. 4. Compute a new threshold value:
µ1 + µ 2
T=
2
5. Repeat steps 2 – 4 until the difference in T in successive iterations is
less than a predefined limit T∞
This algorithm works very well for finding thresholds when the histogram is suitable
30. Problems With Single Value Thresholding
Single value thresholding only works for bimodal histograms
Images with other kinds of histograms need more than a single threshold
31. Single value thresholding only works for bimodal histograms
Images with other kinds of histograms need more than a single threshold
