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). Here 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. 

Layer

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. 

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 2^nd 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

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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