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CMUcam Tom Kneeland
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CMUcam – What is it? Digital Camera with an onboard microcontroller Track a blob based on programmable color thresholds Calculate centroid Calculate mean color and variance RS-232 or TTL ~17fps
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Components – CMOS Camera Omnivision OV6620 Color Camera 17 MHz clock 8 bit RGB or YCrCb* 8 or 16 bit bus Max Resolution: 356 x 292 60 fps
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Components - Microcontroller Ubicom SX28 RISC Architecture 28 pin DIP 75 MIPS @ 75 MHz 2048 words of ROM 136 bytes of SRAM
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How Does It Work – Firmware Written in C 2035 of the 2048 words of ROM 135 of the 136 bytes of SRAM Color Blob Tracking Frame Dump Line Mode Color Statistics Two serial IO protocols
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How Does It Work - Configuration Camera Resolution: 176 x 144 8-bit bus RAM Allocation –80 bytes for a pixel buffer (one row) –56 bytes for processing Effective Resolution: 80 x 144
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How Does It Work – Pixel Format 8 bit RGB or YCrCb –4:2:2 RGBG –8-bits per component –Macropixel = 2 image pixels –Red and Blue are shared –16 bpp
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How It Works – Pixel Format 16 bpp x 80 pixels = 160 bytes! Convert to a 2:1:1 format Skip every other pixel Share Red and Blue Values Sacrifices resolution and color accuracy
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Color Blob Tracking Compare each pixel to min and max values Determine if they fall within bounding box Confidence Measure: –#pixels/box_area * 256 Centroid –Sum x,y of matched pixels –Divide by num detected pixels
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Frame Dump and Line Mode Frame Dump –Limited by serial I/O –One or Two Columns at a time Line Mode –Line by Line binary image of detected pixels –Available during blob tracking
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ASCII Protocol cr – program camera registers sw – set window (bounding box) coords gm – get mean value –S R mean G mean B mean R deviation G deviation B deviation tc – track color function –M x cen y cen x 1 y 1 x 2 y 2 #pixels confidence
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ASCII Protocol Example CMUcam v1.2 :cr 18 44 17 2 19 32 ACK :sw 30 60 50 80 ACK :pm 1 ACK :gm ACK S 150 20 30 5 2 6 :pm 0 ACK :sw 0 0 80 143 ACK :tc 145 18 24 155 22 36 ACK M 50 80 38 82 53 128 35 98 M 52 81 38 82 53 128 35 98 M 51 80 38 84 53 128 35 98
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