Colour bit depth questions.

[AstroBenny]

I'm trying to learn a little bit about colour (not color :P) bit depth before I indulge myself in my 10hr Lynda Photoshop course. 

I've read this:

"Bit depth quantifies how many unique colors are available in an image's color palette in terms of the number of 0's and 1's, or "bits," which are used to specify each color. This does not mean that the image necessarily uses all of these colors, but that it can instead specify colors with that level of precision. For a grayscale image, the bit depth quantifies how many unique shades are available. Images with higher bit depths can encode more shades or colors since there are more combinations of 0's and 1's available."

Source: http://www.cambridgeincolour.com/tutorials/bit-depth.htm

When it says "unique colours" does it mean that as in different shades of colour or actually different colours?

And how come grayscale images are only shades of white/black and not the full spectrum of RGB?

Thirdly, where do the values of 0-255 come into all of this.

Sorry if this doesn't make sense - I'm confused 

 

[Samfisher]

Shades of colours = unique colours. It may be called "red", but it's still a different shade of red and therefore a different colour in the whole scheme of things.

RGB is 24-bits of colours, divided by 3 it's 8 bits per colour, so that equals 0-255 (256 values per colour)

[Enderman]

8 bit is 2^8 = 256 colours

when we talk about RGB, each colour (red green and blue) has its own 256 levels, all the way from 0 to 255

this means you have 256^3 which is also 2^24 aka 24 bit

 

32 bit is when you add an extra alpha (transparency) channel, so you have RGBA

so you have four different options, and the combination is then 256^4 which is also 2^32 aka 32 bit

 

grayscale basically means white to black and everything in between

there should be no colour in grayscale

[AstroBenny]

1 minute ago, Enderman said:

8 bit is 2^8 = 256 colours

when we talk about RGB, each colour (red green and blue) has its own 256 levels, all the way from 0 to 255

this means you have 256^3 which is also 2^24 aka 24 bit

 

32 bit is when you add an extra alpha (transparency) channel, so you have RGBA

so you have four different options, and the combination is then 256^4 which is also 2^32 aka 32 bit

 

grayscale basically means white to black and everything in between

there should be no colour in grayscale

What does the transparency channel do?

[Enderman]

1 minute ago, AstroBenny said:

What does the transparency channel do?

it makes it transparent or not, so you can see whats behind

if the alpha channel is at 255 (max transparency) then you cant see any of the RGB, you see whats behind

if alpha channel is at 0 then you see all RGB and you cant see through the image

if the alpha channel is somewhere in between, what you see is a combination of RGB of your image plus whatever is behind it, such as your background or whatever

[AstroBenny]

Just now, Enderman said:

it makes it transparent or not, so you can see whats behind

if the alpha channel is at 255 (max transparency) then you cant see any of the RGB, you see whats behind

if alpha channel is at 0 then you see all RGB and you cant see through the image

if the alpha channel is somewhere in between, what you see is a combination of RGB of your image plus whatever is behind it, such as your background or whatever

Cheers.