Lecture 7: Sounds & ImagesAnnouncementsGoals for TodayFiltering ReviewMore on FilteringGenerating Signals: Electronic MusicGenerating Signals: SpeechChanging a VoiceOn to Images!Images vs. Sounds in Digital FormBits Mapping to Gray LevelsZooming in on an ImageEffect of Changing Pixels/InExamples of Bit TradeoffsLecture 7: Sounds & ImagesThe Digital World of MultimediaProf. Mari OstendorfEE299 Lecture 723 Jan 2008Announcements Another office hour change: Friday change to 10-12; Thurs 1:30-3:00 Problem with Lab dropbox is fixed – try again This Friday: Guest Lecture Color Vision Prof. Maya Gupta, UW EE Tomorrow EE lecture of interest Retinal local adaptation for the tone mapping of color filter array images Prof. Sabine Susstrunk, EPFL 1/24, 4pm, EEB 403EE299 Lecture 723 Jan 2008Goals for Today Review: Filtering Collaborative quiz Signal generation Intro to Digital ImagesEE299 Lecture 723 Jan 2008Filtering ReviewLow Pass FilteredHigh Pass FilteredOriginal SignalLow pass filter:Keep low & remove high frequenciesHigh pass filter:Keep high & remove low frequenciesEE299 Lecture 723 Jan 2008More on Filtering Can also be used to “shape” frequency content Any function of the formy(n)=a1 y(n-1)+a2 y(n-2)+…+ap y(n-p)+b0 x(n)+b1 x(n-1)+…+bm (n-m)can be used to shape/change frequency content (input is x(n), output is y(n)) Leads us to the idea of generating signalsEE299 Lecture 723 Jan 2008Generating Signals: Electronic MusicNotes(specify fundamental frequency)Cosine(+Harmonic)GeneratorFrequencyShaperPick the filter with a frequency shape that matches the desired instrument instrument(frequency domain)EE299 Lecture 723 Jan 2008Generating Signals: SpeechCosine(+Harmonic)GeneratorFrequencyShaperPick the….• source signal depending on whether sound is voiced/unvoiced, and• filter with a frequency shape that matches the desired sound (ae,s,l,m,…)NoiseGeneratorpitchswitchvoicedunvoicedAlternative: glue together sounds snipped from a similar context(frequency domain)EE299 Lecture 723 Jan 2008Changing a Voice Identify the system (frequency shape) associated with a particular sound Use a different source function with this system (e.g. robot-like voice with constant pitch)EE299 Lecture 723 Jan 2008On to Images! Grayscale sampled images are 2D version of sampled sounds Color images: 3xgray (for mixing 3 colors) More on Friday Images have frequencies too!  … so can have aliasing, filtering, etc. More next weekEE299 Lecture 723 Jan 2008Images vs. Sounds in Digital Form Sounds: Bits = sec x samples/sec x bits/sample Samples/sec = sampling rate Bits/sample = quantizer resolution Gray-scale images: Bits = inches horizontal x pixels/in (H) x inches vertical x pixels/in (V)x bits/pixel Pixels/in = spatial resolution Bits/pixel = gray scale resolutionEE299 Lecture 723 Jan 2008Bits Mapping to Gray LevelsDecimal Binary Shade0 000 black1 001 very dark gray2 010 dark gray3 011 medium gray4 100 light gray5 101 very light gray6 110 hint of gray7 111 whiteEE299 Lecture 723 Jan 2008Zooming in on an ImageTry MATLAB zoom with imshowEE299 Lecture 723 Jan 2008Effect of Changing Pixels/InEE299 Lecture 723 Jan 2008Examples of Bit Tradeoffs See Orsak et al. pp 146-147 1 bit per pixel (bpp) vs. 8 bpp