Courseware download: ftp:/bcc.hitsz.edu.cn/DigitalImageProcessing/username: download password: downloadDigital Image Processing: Digital Imaging FundamentalsDr. Guangming Lu Luguangmgmail.com3 of 58ContentsMain purpose: introduce several concepts related to DIP and some of the notation used throughout the course. This lecture will cover: Human vision system Light and Electromagnetic spectrum Image acquisition Sampling and Quantization Resolution Basic Relationships Between Pixels4 of 58Human Visual SystemuThe best vision model we have! uKnowledge of how images form in the eye can help us with processing digital images uWe will take just a whirlwind tour of the human visual system5 of 58Structure of the Human EyenThe lens focuses light from objects onto the retina nThe retina is covered with light receptors called cones (6-7 million) and rods (75-150 million) nCones are concentrated around the fovea and are very sensitive to colour nRods are more spread out and are sensitive to low levels of illumination6 of 58Structure of the Human Eye7 of 58Blind-Spot ExperimentDraw an image similar to that below on a piece of paper (the dot and cross are about 6 inches apart)Close your right eye and focus on the cross with your left eye Hold the image about 20 inches away from your face and move it slowly towards you The dot should disappear!8 of 58Brightness Adaptation & Discriminationn Because digital images are displayed as a discrete set of intensities, the eyes ability to discriminate between different intensity levels is an important consideration in DIP results. n The human visual system can perceive approximately 1010 different light intensity levels n Subjective brightness is a logarithm function of the light intensity incident on the eye. n However, at any one time we can only discriminate between a much smaller number brightness adaptation 9 of 58nFor a given set of conditions, the current sensitivity level of the visual system is called the brightness adaptation level.Brightness Adaptation & Discrimination10 of 58Brightness Adaptation & Discrimination (cont)Perceived brightness is not a simple function of intensity： Mach Bands(1865)Seeing is believing? 11 of 58Brightness Adaptation & Discrimination (cont)nSimilarly, the perceived intensity of a region is related to the light intensities of the regions surrounding it12 of 58Brightness Adaptation & Discrimination (cont)Another experiment: a piece of paper on a desk is always white, but can appear totally black when used to shield the eyes while looking directly at a bright sky13 of 58Optical IllusionsOur visual systems play lots of interesting tricks on us14 of 58Optical Illusions (cont)15 of 58Light and the Electromagnetic SpectrumNewton, 1666 Violet, Blue, Green, Yellow, Orange, and Red Blends smoothly into the next.Light is just a particular part of the electromagnetic spectrum that can be sensed by the human eye16 of 58Light and the Electromagnetic Spectrum17 of 58Light and the Electromagnetic SpectrumnVisible light: 0.430.79um nThe electromagnetic spectrum is split up according to the wavelengths of different forms of energyWhere c is the speed of the light, v is the frequency, and h is the Plancks constant18 of 58Light and the Electromagnetic SpectrumlA stream of massless particles lEach massless particle contains a certain amount of energy. lEach bundle of energy is called a photon lHigh frequency electromagnetic phenomena carry more energy per photon. That is the reason that gamma rays are so dangerous to living organisms. 19 of 58Light and the Electromagnetic SpectrumnThe colours that we perceive are determined by the nature of the light reflected from an object nFor example, if white light is shone onto a green object most wavelengths are absorbed, while green light is reflected from the objectWhite LightColours AbsorbedGreen Light20 of 58Light reflectance propertiesA body that reflects light and is relatively balanced in all visible wavelengths appears white to the observer. A body that favors reflectance in a limited range of the visible spectrum exhibits some shades of color. Achromatic or monochromatic light: the only attribute is intensity-Gray-level Black to Gray to WhiteLight and the Electromagnetic Spectrum21 of 58Chromatic light Three basic quantities to describe the quality of a chromatic light source: Radiance (Watts: W)（发光强度） The total amount of energy that flows from the light source. Luminance (lumen: lm)(光通量） A measure of the amount of energy an observer perceives from a light source. Example: Far Infrared Region Brightness Subjective descriptor of light perception that is practically impossible to measure.Light and the Electromagnetic Spectrum22 of 58Light and the Electromagnetic SpectrumnIn principle, if a sensor can be developed that is capable of detecting energy radiated by a band of the electromagnetic spectrum, we can image events of interest in that band. nHowever, the wavelength of an el