《人眼视觉特性》PPT课件.ppt

要点：,人眼视觉人眼非正常视觉人眼错觉,人眼视觉特性,人眼视觉,感光细胞(photoreceptor cells)：杆状细胞(rod)：单色夜视 锥状细胞(cone)：彩色视觉 红(red)绿(green)蓝(blue)Primary Color 基色,Light enters the retina on the side containing the optic nerves and travels through all the layer before reaching the receptors.,Retina,This animated cartoon illustrates how light(white dot)enters the retina on the side containing the optic nerves and travels through all of the retinal layers before finally being absorbed by the photopigments in the outer segments of the receptors.A neural signal(yellow dot)is generated in the receptors which then travels through the neurons of the various retinal layers and finally travels out through the optic nerve up to the lateral geniculate nucleus.,How light enters the retina and is transmitted out the optic nerve,Electron Micrograph of Human Visual Receptors,When looking at an object that is far away the lens is kind of skinny.What happens when looking at a nearby object?,Refraction,When looking at nearby objects the lens gets fatter,causing the image of the object to be focused on to the retina in the fovea.What would happen if the lens did not get fatter?By the way,the technical term for this change in lens shape is accommodation.We frequently call it focusing.,If the lens can not properly focus light on the retina,the image will fall either behind or in front of the retina.Can you guess what would happen if the lens is too fat?,If you guessed that when the lens is too fat that light is focussed in front of the retina,you were right.Is there a remedy for lens problems that do not allow light to be properly focused on the retina?Sure.,Many people wear contact lenses to help image light properly on to the retina.Another solution is for a person to wear glasses.This places a lens in front of the eye not on the cornea as is the case with contact lenses.A recent solution is to use a laser to reshape the cornea.this solution is possible only in some cases.,There are two kinds of astigmatism:1.lenticular and 2.corneal.Astigmatism occurs when the surface of the cornea or of the lens is not perfectly smooth.If,for example,there is a small flat spot on your cornea the image in a certain direction on your retina will not be in perfect focus.If the figure on the right was constructed with all the radial lines of equal sharpness and contrast a person without astigmatism would see all these radial lines as perfectly sharp and with the same contrast.The diagram on the right has been fudged to illustrate how it might appear to a person with astigmatism.This condition can be corrected with a corneal contact lens or cylinder lens in a pair of spectacles.,Astigmatism,Contact Lenses,A very thin plastic lens,often flexible(soft lenses)floats on a layer of tears on the corneal surface of the eye.These lenses can be of the permanent variety or disposable.The permanent variety need to be properly cleaned and cared for.The disposable are often worn continuously and the thrown,Corneal Contact Lens,away when removed.Note how the bottom edge of the lens is against the lower eye lid.If the wearer looks down,the lens is pushed up a little.This trick can be used to provide bifocal contact lenses.These lenses have different powers in the center than in the periphery.When the wearer looks down to read the lens is moved to a new position to facilitate seeing sharply at normal reading distances.If there is an irregularity on the cornea(astigmatism)it is automatically corrected by the combination of the tear layer and the contact lens.,A cylinder lens is different than a spherical lens which is what one normally sees in spectacles.Although a cylindrical component my be built in to that which appears spherical.As can be seen in the left diagram a cylinder lens has power only in one axis.In the left it is the horizontal axis.This lens does not refract light in the vertical direction.,Cylinder lens,Spectral Sensitivity Curves of Rods&Cones,When you first enter an extremely bright environment,for example,when emerging from a dark movies house into a very bright sunlit area the man carving the duck would appear like this.But in less than a minute he will appear as seen below.In the left photo the contrast is very low.Below the contrast is normal.When light adapted a scene might look like this.,Dark Adaptation,For approximately the first 10 minutes in the dark,the cones require less light to reach a threshold response than do the rods.Thereafter,the rods require less light.The point at which the rods become more sensitive is called the rod-cone break.,Dark Adaptation Function,p.18,The following demonstration is an example of how the worldappears to a person with asevere type of color blindness,deuteranopia.See how you would do in a colorblind world,人眼视觉,Color vision defects cause problems in the real world,Which meat is the most,thoroughly cooked?,Which meat is the most,thoroughly cooked?,Which flask contains a light pink,solution?,Which flask contains a light pink,solution?,Which of the following slides,contains a pink cell?,Which of the following slides,contains a pink cell?,Which picture contains a red,crayon?,Which picture contains a red,crayon?,The use of color so that color blind people(and everyone else)can see what you are presenting.,In its most severe forms,color blindness is caused by the absence of one of the cone visual pigments.Shown here,the spectral sensitivities of the cone pigments in color normaltrichromats are compared with those of a color blind person.Also compare the spectrum as it appears to a color normal person with the illustration of how it might look to a red-green color blind person.,The difficulties with certain colors can be illustrated on a color wheel.For a severely red-green color blind person there are only two hues,the ones a color normal person sees as yellow and blue.Intermediate colors,the ones seen as blueish-green and magenta,appear gray.,Clear graphics are very important and often the source of the most difficulty;here are two examples showing the difference between good and bad use of color.The Trick is to keep brightness differences large and to avoid color combinations that do not contrast well.,A comparison of the two color wheels shows which color combinations would be difficult to see.Graphics cause the most problems,but the colors can be economically illustrated as text examples,below.The right-hand column illustrates how the left hand column might look to a color blind person.,Some examples of color combinations that are easily seen by a color blind person are shown below.These are illustrated as text examples but these principles are most important to keep in mind when preparing drawings,graphs,and figures.,cone,狗是色盲？,点击图片播放视频,眼见为实？,马赫带效应,Mach bands,Boynton Illusion,Color Influences Distance Perception,Radiating Lines,Take two pieces of paper and place their edges as close as possible to both sides of one red diagonal.Note that the red square in the middle is the same as all the other squares on that diagonal.Now move your pieces of paper to expose mainly the red squares on the other diagonal.On this diagonal all the red squares,including the center one,are again the same color red.Because the center square is common to both diagonals this exercise proves that all the red squares in both diagonals are exactly the same red color.Yet,when the pattern is seen as a whole,the two red diagonals appear different from each other,Color Assimilation,Hermann Grid Illusion,点击图片 播放FLASH,Hering&Pogendorf Illusions,点击图片 播放FLASH,Which line is longer,the red one or the green one?Use a ruler to find out.You will probably be surprised.,Horizontal-Vertical Illusion,点击图片 播放FLASH,Look at the upper right figure.This experiment works better if you close one eye.Fixate on the black dot in the center for about 10-15 seconds.Pay close attention to what you see.Now do the same thing with the upper left figure.Did you notice any difference?In the accompanying explanation I tell you what most people see and the reason for it.,Stabilization Causes Fading,This is called a Kanizsa figure after the person who invented it.If you look carefully you will probably see the edges of the entire triangle,even though the triangle is defined only by the notches in the red disks.,Kanizsa Illusion,Which is longer,the red line or the blue line?Use a ruler to find out the answer.Select the answer to double check on your result.,Mueller-Lyer Illusion,点击图片 播放FLASH,The round dots are all exactly the same color gray.I merely created the one on the extreme right and then copied it to each of the darker rectangles.Clearly,the lightness of the background effects the way in which we perceive the center gray dot.This effect is called simultaneous contrast.Again,as can be seen in other demonstrations,the perception of this kind of display is a result of lateral interactions.,Simultaneous Contrast,The circular area in each quadrant in the left figure is exactly the same color.The different appearance is due to the surround and the lateral interactions that occur.On the right I merely changed the background colors so that they are all identical.You can now see that the circular areas are,indeed,identical.This phenomenon is called simultaneous color contrast.,Simultaneous Contrast,Necker Cube Illusion,Perspective Illusion,点击图片 播放FLASH,What do you see in this diagram?In order to find out what people often say they see select possible perceptions.,点击图片播放视频,点击图片播放视频,点击图片 播放FLASH,更高层次的视觉认知心理文化,红 白 黑 黄 绿,电影利用了人眼的视觉特性,点击图片播放视频,电影利用了人眼的视觉特性,点击图片播放视频,视觉暂留,视觉暂留,点击图片播放视频,快拍慢放,点击图片播放视频,慢拍快放,点击图片播放视频,点击图片播放视频,Terms,Photoreceptor cells:感光细胞 Rod:杆状细胞Cone:锥状细胞Retina:视网膜Iris:虹膜Fovea:中央凹Visual cortex:视觉皮层,