2a bitmapped graphics hardware
DESCRIPTION
TRANSCRIPT
Bit-Mapped Graphic Data:Input (Capture) Hardware
Multimedia – Section 2
CCD & ADC
• CCD (charged coupled device):• Uses sensors to capture light and then
convert into analogue electrical signals.• Currently only see light levels not colour
• ADC (Analogue/Digital Converter)• Converts the analogue signals into digital
signals so that the computer can process them.
Digital Camera
• In a digital camera a CCD array captures light coming in through a lens
• The Resolution is the number of pixels in the image produced
• Capturing colour– A colour filter array is placed over the CCD array– Each sensor records light of one colour (red, green or blue)
Scanner
• Requires 3 images for colour– Red, Green & Blue
• Capture images from a flat object
• Linear CCD– Narrow strip passes over image.
Multimedia - Section 2
Bit-Mapped Graphic Data:Storage of Graphic Data
File Formats• Bitmap (BMP)• Graphic Interchange Format (GIFF)• Joint Pictures Expert Group (JPEG)• Portable Network Graphics (PNG)
Bitmap File FormatUncompressed:
– A file which holds a binary number for each pixel in an image
Limitation:– large file size
Compression: – RLE (Run Length Encoding)
• uses the fact that large areas have same colour of pixel. (LossLess)
Extension: – .bmp
Bitmap File Format
Colour Depth
• The number of colours that can be represented
• Calculation:
Number of colours = 2 bit depth
Example
Colour (bit) Depth = 8Number of colours = 28
= 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2
= 256
GIF File Format• Lossless compression
– LZW
• Limited number of colours: limited to 28
– 256 colours
• Features: – Animation– Transparency
• Extension: .gif
GIF File Format
Good For:• Flat areas of colour• Few colours• Animated images• Transparency
Bad For:• Photographic images• High colour graphics• High quality videos
Interlacing• Allows you to view an image before it is
downloaded• Image is gradually revealed
JPEG File Format• Lossy compression
– DCT
• Greyscale or full-colour image compression • Exploits human eye limitations• Related to MPEG• Extension: .jpg
JPEG File Format
• Advantages:– Greater compression than lossless– Good for photographic images (real-world)– Compression ratio can be controlled by user– Best for large files
• Disadvantages– Doesn’t support interlacing or transparency
PNG File Format• Has all advantages of GIF without the
restrictions
• Allows 24 bit colour
• Allows for partial transparency
• Lossless compression– Variation of LZW
• Extension: .png