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ITMA04 Digital Imaging
ITMA04 Digital Imaging
ITMA04 Digital Imaging
ITMA04 Digital Imaging
ITMA04 Digital Imaging
ITMA04 Digital Imaging
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ITMA04 Digital Imaging

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  • 1. Where do digital images come from? • Scanners ITMA 04 – e.g. Flatbed, Film, Drum Introduction to Digital Imaging g g g • Digital Cameras • Computer-aided – e.g. AutoCAD, Adobe Illustrator Krates Ng Fall 2008 • Computer-generated – e.g. fractal 2 10/2/2008 11:13 AM ITMA10 Krates Ng Fractal examples • Java-based online Fractal generator Two main categories – http://www.david-lindsay.co.uk/old/mandelbrotIE.html • Fractal movie: – http://www.fractal-recursions.com/files/anim/anim.html • Raster (bitmap) and Vector • Tree growth simulation: – http://hk.youtube.com/watch?v=69QWy0EGkjo Raster Vector at 6× magnification at 6× magnification 3 4 10/2/2008 11:13 AM ITMA10 Krates Ng 10/2/2008 11:13 AM ITMA10 Krates Ng Raster format Size of a raster image • Also known as bitmap. • Good for representing continuous tones. y • Grid/matrix structure. • The computer needs to know how every pixel to be colored. colored x • Jagged when magnified (resolution dependent). • Storage size does not depend on complexity of the image. • Total bits required = x ⋅ y ⋅ bit depth • Can be efficient to display because of modern hardware • Typical bit depth is 24-bit (true color), but design. could be 16-bit or 8-bit. • Difficult to convert to vector format. • Common formats: .gif, .bmp…etc. • x : y = aspect ratio (e.g. 4:3, 16:9, 16:10) 5 6 10/2/2008 11:13 AM ITMA10 Krates Ng 10/2/2008 11:13 AM ITMA10 Krates Ng 1 K.Ng Sept08
  • 2. Common Display Sizes Size of a raster image – an example • If an image has a resolution of 1024×768 at true color, what is the storage required? • Total bits required = 1024 × 768 × 24 • = 18,874,368 bits • or ÷8 = 2,359,296 bytes • or ÷1024 = 2,304 kilobytes • or ÷1024 = 2.25 megabytes From: http://upload.wikimedia.org/wikipedia/en/e/e5/Vector_Video_Standards2.svg 7 8 10/2/2008 11:13 AM ITMA10 Krates Ng 10/2/2008 11:13 AM ITMA10 Krates Ng Common raster file formats Vector format • Good for representing drawings that can be easily described mathematically. File format Max. no. of colors Compression type • e.g. the line example, only need to know the two endpoints. BMP 16M None • Smooth no matter at what magnification level (i.e GIF78a GIF89a GIF78a, 256 Lossless resolution independent). independent) JPEG 16M Lossy • Usually small storage size. • Complex image can be inefficient to display. PNG-8/-24 256/16M Lossless • Convert to raster format easily. TIFF 16M Lossless • Common format: .ai (Adobe Illustrator), .swf (Macromedia Flash), SVG…etc. 9 10 10/2/2008 11:13 AM ITMA10 Krates Ng 10/2/2008 11:13 AM ITMA10 Krates Ng Digital imaging Quantization • Pixel: picture element, the smallest unit that makes up the image. • Computers use binary. binary • Capturing real images involves Analogue- to-Digital Conversion (ADC), e.g. by digital camera or scanner. 11 24=16 levels 12 10/2/2008 11:13 AM ITMA10 Krates Ng 10/2/2008 11:13 AM ITMA10 Krates Ng 2 K.Ng Sept08
  • 3. Bit depths Digital Camera • Overtaking traditional film cameras. Black & white: 1 bit per pixel 16 Grey levels: 4 bits per pixel 256 Grey levels: 8 bits per pixel from www.canon.com 13 14 10/2/2008 11:13 AM ITMA10 Krates Ng 10/2/2008 11:13 AM ITMA10 Krates Ng How digital SLR cameras work? How Digital Compact Camera Works? From www.canon.com 15 From www.canon.com 16 10/2/2008 11:13 AM ITMA10 Krates Ng 10/2/2008 11:13 AM ITMA10 Krates Ng Digital Camera – Image Sensor Single-chip CCD – Bayer filter • Charge-coupled device(CCD) / CMOS • Invented by Bryce Bayer of Eastman Kodak. • Produces electric charge proportional to the • Green photosensors: light intensity. intensity luminance-sensitive elements. • Red and blue ones: chrominance-sensitive elements. 16.7M CMOS image sensor used in Canon EOS-1Ds DALSA FTF3020C 6M color CCD Mk.II 36mm x 24mm full-frame 17 From wikipedia.com 18 10/2/2008 11:13 AM ITMA10 Krates Ng 10/2/2008 11:13 AM ITMA10 Krates Ng 3 K.Ng Sept08
  • 4. De-mosaic Algorithm 3-CCD Video Camera • Uses a Dichroic beam splitter prism. • Splits the image into R, G and B components. from sony.com from wikipedia.com 19 20 10/2/2008 11:13 AM ITMA10 Krates Ng 10/2/2008 11:13 AM ITMA10 Krates Ng New Generation of CCD – Foveon X3 They claim it’s better… from www.foveon.com from www.foveon.com 21 22 10/2/2008 11:13 AM ITMA10 Krates Ng 10/2/2008 11:13 AM ITMA10 Krates Ng Sensor Sizes Where you can find X3 camera? • Sigma SD-10 • Polaroid X530 • US$1260.00 • US$380.00 From: www.cambridgeincolour.com 23 24 10/2/2008 11:13 AM ITMA10 Krates Ng 10/2/2008 11:13 AM ITMA10 Krates Ng 4 K.Ng Sept08
  • 5. Typical Cameras Bigger Sensors = ? • In general, = better image qualities • 1/7”~1/4” (1.85x1.39mm~3.2x2.4mm) – Less noise Camera-phones, webcams – More sensitive to light (ISO setting) • 1 / 2.3 CCD (6 16 4 62 ) 2 3” (6.16x4.62mm) – Better dynamic range Canon A2000IS Casio EX-Z200 SONY DSC-T500 • 1 / 1.7” CCD (7.6x5.7mm) Canon G10 • 1 / 6.3” CCD Panasonic LX3 25 26 10/2/2008 11:13 AM ITMA10 Krates Ng 10/2/2008 11:13 AM ITMA10 Krates Ng DSLRs Color System • 23.6x15.8mm (crop factor 1.5) • Red-Green-Blue color SONY a200 Nikon D90 system. • Additive system. • 22 2x14 8mm ( f 1 6) 22.2x14.8mm (crop factor 1.6) Canon 450D • Monitor screen. • 36x23.9mm (full frame) 36x24mm (full frame) Nikon D3 D700 Canon EOS 1Ds III 5D II 27 28 10/2/2008 11:13 AM ITMA10 Krates Ng 10/2/2008 11:13 AM ITMA10 Krates Ng Color temperature • CMYK color system. • 0K= -273.16°C • C=Cyan, M=Magenta, Y- C • 1500K Candlelight • 2680K 40W incandescent lamp Yellow, K=Black. • 3000K 200W incandescent lamp • Subtractive system. • 3200K Sunrise/sunset K • 3400 Tungsten lamp • Use in printing. • 4500-5000K Xenon lamp M Y • 5500-5600K Electronic photo flash • 6500-7500K Overcast sky • 9000-12,000K Blue sky 29 30 10/2/2008 11:13 AM ITMA10 Krates Ng 10/2/2008 11:13 AM ITMA10 Krates Ng 5 K.Ng Sept08
  • 6. White Balance (WB) Lossy Compression • JPEG (Joint Photographic Expert Group). • Uses visual perception – We are more sensitive to moving objects and Incorrect WB Correct WB edges rather than gradual transitions. – We are more sensitive to red and green rather than blue light. – We are more sensitive to changes in brightness Nikon P50 WB Menu than color. 31 32 10/2/2008 11:13 AM ITMA10 Krates Ng 10/2/2008 11:13 AM ITMA10 Krates Ng In-class Project - Morphing www.morphthing.com 33 10/2/2008 11:13 AM ITMA10 Krates Ng 6 K.Ng Sept08

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