Compressed? Uncompressed?

Current default = Lossy compression

Generation Loss

Uncompressed

• No generation loss
• Dead simple (=preserves well)
• The largest possible version (ca. 1.3 GB/minute PAL SD)
• There’s more than just 1 “uncompressed”

Calculating filesize: IMAGE

• Width(px) x Height(px)
• x Bits-Per-Pixel(bpp)
• x FPS
• / 8 = 1 second (in Byte)

Calculating filesize: AUDIO

• Samplerate x bit-depth
• x channels (even if silence!)
• / 8 = 1 second (in Byte)

Lossless

“It’s like ZIP for film!”

• No generation loss
• Way larger than lossy
• But: Smaller than uncompressed

Behind the Scenes: Algorithms

Run Length Enoding (RLE)

• Uncompressed: BBBBBBBBGGBBBBBRRRBBBB = 19 Bytes
• Compressed: 8B2G5B3R4B = 10 Byte

Huffman

Source: Indiana University

Huffman Tree

Huffman Code

Lossy

JPEG

Terms used

• lossy
• lossless
• uncompressed
• data reduced format
• compressed
• near-lossless
• visually lossless
• mathematically lossless

Format examples: VIDEO

Compression: Spatial and Temporal

A/V allows to apply compression in 2 ways:

• Spatial: Inside an image
• Temporal: Between images

Spatial compression: Examples

• Audio: Differential pulse-code modulation (DPCM)
• Video: GOP, Motion estimation

Data rate / Bitrate

“Data per time”

• Mbps / 8 = MB / second
• MB/s * 60 = MB / minute
• MB/min * 60 = MB / hour

Data rate / Bitrate

• Higher bitrate =
  larger files, higher quality

• Lower bitrate =
  smaller files, lower quality

• “Better” format =
  Same size, better quality - OR:
  Smaller size, same quality.

Links

• Huffman coding (Indiana.edu)
• EETimes: Data compression tutorial:
  • Part 1,
  • Part 2 (LZW),
  • Part 3 (JPEG + MPEG)
• Introduction to Data Compression (blellochcs.cmu.edu, 2013)

Comments?

Questions?