MC图像与视频的冗余：知识冗余 ◆有许多图像的理解与某些基础知识有相当大的相关 性。例如：人脸的图像有固定的结构。嘴鼻子，眼睛 等具有固定的对称和位置关系。这类规律性的结构可 由先验知识相背景知识得到，我们称此类冗余为知识 冗余。 11 ynh.cxh@ustc.edu.cn
{ynh,cxh}@ustc.edu.cn 图像与视频的冗余：知识冗余 有许多图像的理解与某些基础知识有相当大的相关 性。例如：人脸的图像有固定的结构。嘴鼻子，眼睛 等具有固定的对称和位置关系。这类规律性的结构可 由先验知识相背景知识得到，我们称此类冗余为知识 冗余。 11
K心图像与视频的冗余：视觉冗余 ◆人类视觉系统对于图像场某些变化是不能感知的。 口人类视觉系统一般的分辨能力约为26灰度等级 口对亮度变化敏感，而对色度的变化相对不敏感 口在高亮度区，人眼对亮度变化敏感度下降 ▣对物体边缘敏感，内部区域相对不敏感 口对整体结构敏感，而对内部细节相对不敏感。 violet blue 0 8 green -yellow 0.6 orange red 0.4 0.2 400 450 500 550 600 650 700 750 12 Wavelength(nm) ynh.cxh@ustc.edu.cn
{ynh,cxh}@ustc.edu.cn 图像与视频的冗余：视觉冗余 人类视觉系统对于图像场某些变化是不能感知的。 人类视觉系统一般的分辨能力约为26灰度等级 对亮度变化敏感，而对色度的变化相对不敏感 在高亮度区，人眼对亮度变化敏感度下降 对物体边缘敏感，内部区域相对不敏感 对整体结构敏感，而对内部细节相对不敏感。 12 0 0.2 0.4 0.6 0.8 1 400 450 500 550 600 650 700 750 violet blue green yellow orange red Photopic luminous efficiency Wavelength (nm)
MC 图像与视频的冗余：视觉冗余 HVS:视觉敏锐度(visual acuity) The ability of the eye to resolve detail is known as "visual acuity.The normal human eye can distinguish patterns of alternating black and white lines with a feature size as small as one minute of an arc (1/60 degree or /(60*180)radians). A few exceptional eyes may be able to distinguish features half this size.But for most of us,a pattern of higher spatial frequency will appear nearly pure gray. Low contrast patterns at the maximum spatial frequency will also appear gray. Spatial frequency is typically measured in cycles or line pairs per millimeter (Ip/mm),or cycles per degree (CPD). (ynh,cxh @ustc.edu.cn
{ynh,cxh}@ustc.edu.cn 图像与视频的冗余：视觉冗余 HVS：视觉敏锐度(visual acuity) The ability of the eye to resolve detail is known as "visual acuity." The normal human eye can distinguish patterns of alternating black and white lines with a feature size as small as one minute of an arc (1/60 degree or π/(60*180) radians). A few exceptional eyes may be able to distinguish features half this size. But for most of us, a pattern of higher spatial frequency will appear nearly pure gray. Low contrast patterns at the maximum spatial frequency will also appear gray. Spatial frequency is typically measured in cycles or line pairs per millimeter (lp/mm), or cycles per degree (CPD). 13
Me 图像与视频的冗余：视觉冗余 contrast sensitivity vs.spatial frequency 10 0.1 isenuoo 0.01 0.001 3 10 30 100 Spatial frequency (cpd) 14 ynh.cxh @ustc.edu.cn http://en.wikipedia.org/wiki/Contrast_(vision)
{ynh,cxh}@ustc.edu.cn 图像与视频的冗余：视觉冗余 contrast sensitivity vs. spatial frequency 14 http://en.wikipedia.org/wiki/Contrast_(vision)
MC 对比度敏感函数 Contrast Sensitivity Function (CSF) Contrast sensitivity function(CSF) 在空间或时间上两相 鈿 Full equation 0.8 Dc removed 邻的视觉信号，人眼 刚刚能鉴别出两者差 0.6 别的能力称为视觉系 0.4 统的分辨率。分辨率 02 可用CSF来表示。 0 10 100 10 Angular frequency(cycles/degree) CSF(f)=2.6(0.0192+0.114f)exp(-0.114f)1.1 The dc term(0.0192)can be dropped with very little effect. CSF(f)=(0.0192+0.114f)exp(-0.1254f) The Effects of a Visual Fidelity Criterion on the Encoding of Images ynh.cxh @ustc.edu.cn IEEE Transactions on Information Theory,pp.525-535,Vol.20,No 4,(1974)
{ynh,cxh}@ustc.edu.cn 对比度敏感函数 Contrast Sensitivity Function (CSF) 15 CSF( f ) = 2.6 (0.0192 + 0.114 f ) exp(-0.114 f )1.1 The dc term (0.0192) can be dropped with very little effect. CSF( f ) = (0.0192 + 0.114 f ) exp(-0.1254 f ) The Effects of a Visual Fidelity Criterion on the Encoding of Images IEEE Transactions on Information Theory, pp. 525-535, Vol. 20, No 4, (1974) 在空间或时间上两相 邻的视觉信号，人眼 刚刚能鉴别出两者差 别的能力称为视觉系 统的分辨率。分辨率 可用CSF来表示