05_Segmentation_P2

Image Processing Image Processing Segmentation 1 Process of partitioning a digital image into multiple segments (sets of pixels) 2 Clustering pixels into salient image regions, i e , regions correspon[.]

Image ProcessingSegmentation

1 Process of partitioning a digital image into

multiple segments (sets of pixels).

2 Clustering pixels into salient image regions, i.e.,

regions corresponding to individual surfaces,

objects, or natural parts of objects.

Image ProcessingSegmentation

3 Used to locate objects and boundaries (lines,

curves, etc.) in images

4 Process of assigning a label to every pixel in

an image such that pixels with the same label

share certain visual characteristics.

Image Processing

A Threshold

The objects

in image:

A parameter θ called the brightness threshold is

chosen and applied to the image f(x, y) as follows:

The output is the label "object" or "background" which, due

to its dichotomous nature, can be represented as a Boolean variable "1" or "0"

The original

image:

Image Processing

Fixed threshold

A threshold will be chosen independently of the image data

with the background

2 Compute a new threshold value k:

θk = ( mf,k-1 + mb,k-1 ) / 2

3 k = k +1

The threshold chosen by Isodata algorithm is 139

Isodata algorithm

Isodata algorithm

θ = 116, k=4

Ảnh I:

Ảnh I đã được

phân đoạn với

ngưỡng 116:

Isodata algorithm

θ = 116, k=4

Image Processing

Triangle algorithm

A line is constructed between the maximum of the

histogram at brightness bmax and the lowest value

bmin = (p=0)% in the image

Image Processing

Triangle algorithm

The distance d between the line and the histogram h[b]

is computed for all values of b from b = bmin to b =

bmax

Image Processing

Triangle algorithm

Image Processing

Background-symmetry algorithm

Assumes a distinct and dominant peak for the

background that is symmetric about its maximum

dominant peak (183)

Image Processing

Background-symmetry algorithm

•The maximum peak (maxp) is found by searching for the

maximum value in the histogram

•Searching on the non-object pixel side of that maximum

to find a p% point

Image Processing

Background-symmetry algorithm

the object pixels are located to the left of the background

peak at brightness 183, that mean

h(183) = max {h(a): 0 ≤ h(a) ≤ 255 } = 351 search on the right of that peak to locate to find 95% The total number of pixels in the image is 17424 and the total number of pixels on the right of peak is 8241, about 95% (94.59%) of

17424/2 = 8712.

Image Processing

Background-symmetry algorithm

At which brightness value 5% of the pixels lie to the right (are

above)? This occurs at brightness 216 The number of pixels on the right of 216 is 936, equal to 5% (0.0537) the total number of pixels in the image: 17424.

Because of the assumed symmetry, we use as a threshold a

displacement to the left of the maximum that is equal to the

displacement to the right where the p% is found

2 Nếu diện tích phần 1 lớn hơn một ngưỡng nào đó (ví dụ, có ít nhất vài điểm ảnh) thì kết luận là ảnh I có chứa đám lửa.

G R

(1) Đào Thanh Tĩnh, Hà Đại Dương, Một mô hình phát hiện đám cháy qua ảnh video,

Tạp chí Khoa học và Kỹ thuật, ISSN-1859-0209, tr 5-11, Số 127, 4-2009