Chap 1 Image fundamental

Trends Image processing techniques have

developed from Gray-level processing to color processing 2-D processing to 3-D processing and

reconstruction Static image processing to video

Why use a computer to analyze images? What are the data to be analyzed? What does image analysis consist of?

DigitizationDigitization

2.4 Image sampling and quantization2.4 Image sampling and quantization

Convert the continuous sensed data to digital form

Sampling Spatial transform: spatial coordinates(discrete

locations) Quantization

Amplitude transform: gray levels are converted to discrete values

The quality of a digital image is determined to a large degree by the number of samples and discrete gray levels

Chapter 2: Digital Image FundamentalsChapter 2: Digital Image Fundamentals

2.4.2 Representing digital images2.4.2 Representing digital images

The complete MN digital image in the matrix form: f(x,y)

Pixel, picture element A digital image use a traditional matrix A

The number of gray levels L= 2k

The dynamic range of an image : the range of values spanned by the gray scale

High contrast image : an image whose gray levels span a significant portion of the gray scale as having a high dynamic range

The number, b, of bits required to store a digitized image is

b=M N K

Chapter 2: Digital Image FundamentalsChapter 2: Digital Image Fundamentals

2.4.3 Spatial and gray-level resolution Sampling is the principal factor determining the

spatial resolution Gray-level resolution: the smallest discernible

range in gray level is the power of 2 due to hardware considerations The most common number: 8 bits

Spatial resolution Sub-sampling Re-sampling

Keep the number of samples constant and reduce the number of gray levels

Reduce the number of bits while keeping the spatial constant

Vary N and k simultaneously ISO reference curves

If the number of bit are fixed, how to adjust the trade-off between spatial and gray-level resolution?

Chapter 2: Digital Image FundamentalsChapter 2: Digital Image Fundamentals

Chapter 2: Digital Image FundamentalsChapter 2: Digital Image Fundamentals

Chapter 2: Digital Image FundamentalsChapter 2: Digital Image Fundamentals

Chapter 2: Digital Image FundamentalsChapter 2: Digital Image Fundamentals

Chapter 2: Digital Image FundamentalsChapter 2: Digital Image Fundamentals