Theoretical knowledge of digital image (I) (personal analysis)

One 、 Representation of digital images

An image can be defined as a two-dimensional function $f(x,y)$, among x and y It's space coordinates ,f Is the amplitude at any coordinate point , Represents the brightness of the image at this point . Grayscale is a term used to express the brightness of a black-and-white image , The color image is composed of a single two-dimensional image . for example ,RGB In the color system , A color image consists of three independent component images （ red 、 green 、 blue ） form . Therefore, many image processing techniques are applicable to black-and-white and color images , It is common to both .

1.1.1 coordinate

Image about x and y Coordinates and amplitudes are continuous . To convert such an image into digital form , It requires digitizing coordinates and amplitudes . Digitizing coordinate values is called sampling ; Digitizing the amplitude is called quantization . So when f Of x and y When both components and amplitudes are finite and discrete , The image is called a digital image .

The sampled and quantized results are a real matrix . Suppose that after sampling an image, we get M That's ok N Image of column . We call the size of this image MxN. Coordinate value (x,y) Is a discrete quantity .

** Be careful ：x The scope of is from 0_{M-1 The integer of ,y The scope of is from 0}N-1 The integer of .** chart 2.1(a) This definition is shown .
The tool box uses (r,c) To represent rows and columns , And the origin of the system is （1,1） It's about , so r from 1 To M,c It's from 1 To N The integer of . Pictured 2.1(b) Shown

1.1.2 Represented by the matrix of the image

From the figure 2.1(a) The following digital image functions can be obtained from the coordinate system shown in ：

1.2 Read images 、

2.3 Display images

2.4 Save image

2.4.2 imwrite Second usage

2.5 data type

2.6 Image type

2.6.1 Brightness image

2.6.2 Binary image

2.7 Conversion between data class and image type

2.7.1 Conversion between data classes

2.8 Array index

2.8.1 Vector index

2.8.2 Matrix index