Bit Depth – color shades’ number

Since all medias (sounds, images and video) are now digital, their storing de facto is too. IT is comfortable with these as they are based on a treatment and handling exclusively digital

bit : digital unit

It’s a digital world, its unit : the bit, There is only 2 states : on/off ; black/white; full/empty. And the quantity of bit used for recording,simulate, restore, can be colossal (this is the purpose of the Codecs). Image faites de 0 et 1 : illustration du binaireHere I will focus on the digital coding of the pixel’s (“PICTure ELement”) color in an image, with various numbers of bit :

  • 1 bit : 0 or 1 : black or white : 2 shades
  • 2 bits : 00, 01, 10, 11 : Black, Dark Grey, Light Grey, White : 4 shades
  • 3 bits : 000, 001, 010, 011, 100, 101, 110, 111 : 8 shades
  • 8 bits : 256 shades
  • 10 bits : 1024 shades
  • 24 bits : 16,7 Millions of shades
  • 30 bits : 1,07 Billion of shades
  • 36 bits : 68,7 Billions of shades

For the mathletes : the formula is: n bits=2^n ou 2(power)n or 2x2x2x2x2(n times) shades. 

36 bits
30 bits
30 bits
24 bits
24 bits

Layer

Que ce soit en RVB ou YUV, trois composantes/couches sont utilisées pour la couleur d'un pixel.
Whether it is in RVB or YUV, 3 layers are used for the color of a pixel

8bits_illustr

For a 24 bits image (16,7 Million color shades), they are fairly distributed between each layer: so 8 bits of the red shades, 8 bits for the green shades and 8 bist for the blue shades. 

16bits_illustr

For a 30 bits image (1,07 Billion color shades), they are fairly distributed between each layer : 10 bits for the luminance shades (Y), 10 bits for the first chrominance shades (U) and 10 bits for the 2nd chrominance shades (V).

The fourth alpha layer (optionnal) has its own number of shades, independently of the 3 first layers. 

Bit depth

In a video , the depth of an image is the number of bit of one of the 3 layers

12 bits per layer
10 bits par couche
10 bits per layer
8 bits par couche
8 bits per layer
Color Space Bits / layer Bits / Pixel Shades Data Type
ACES 16-bit 48-bit 328.9 thousand Billion float
Rec. 2020 / P3 DCI 12-bit 36-bit 68.7 Billions integer
Rec. 2020 / Adobe RGB 10-bit 30-bit 1.07 Billion integer
Rec. 709 / sRGB 8-bit 24-bit 16.7 Millions integer

We can note dans the more recent the standard is, the more important is the number of shades to stay coherent this a Gamut even bigger.

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