almost always by the time the image gets
to a monitor it will be an RGB format
because that's the format that the
monitors use so color spaces are a way
of representing the colors in an image
in a different way and a lot of high
definition video uses ycbcr on the other
hand
by the time the colors get to a printer
it'll be in CMYK format because that's
and format printers understand and
that's the color of their links RGB
stands to make green and blue and apart
from being the format we talked about in
velocity videos
it's also format used by monitors so if
you want to show you something on the
screen has been basically put into RGB
format that's how much red we got how
much proof we got and how much green if
we got when you added colors together
you get different colors and indeed when
you had all the colors together you get
white with you take away all the colors
you get black
that's different - let's say the way
that printers work where if you had /
colors together you get black because
you can keep adding colors in with your
inks you eventually get black
so if we draw a RGB diagram here
so if this is red and this is green and
this is blue and halfway between blue
and red will be magenta between blue
and green is cyan and between red and
green is yellow and then between all
three is white and then outside of these
you've obviously got black so you can
create any color you like on your
monitor
by varying the different amounts of
these three colors so on printers
it works like differently so C and Y
and then k is black but we don't tend to
have K as part of this color will use it
to just create black effects because it
works better half way between C and M is
blue and then halfway between C and why
we've got green and then between magenta
and yellow we've got red and in the
middle of all of them
unlike RGB we've got black here so we're
gonna put k for black because we've
already got blue
so this works in a completely different
way to RGB so it's additive so the more
dies we add the darker everything gets
and then we use cage actually just print
in black if we want to
so even though it is not separate round
circle on your diagram
k you would have a at four yeah because
in practice what you might find is that
if you try and add my and see together
to get black in principle it works but
you'll end up of a kind of money .
browning which is just not as good as
just printing in black and you're
wasting a lot of taylor doing that
so who so just put it in black and the
last color space pen look at is ycbcr
variants about commonly used in TV
broadcasting so for example power users
use that color space NTSA using a
similar color space but slightly
different and a lot of high definition
video uses ycbcr what we try to do with
ycbcr is separate the luminosity of
enemies so the intensity of each pixel
from the actual color and by doing that
we can do all kinds of clever things by
down something the color and things will
get onto when we talk a little bit about
JP
this is a picture i took of a flower ok
and this is currently an RGB form and if
we want to split this into ycbcr what we
need to do is take away the gray scale
and and the color and separate them
this is just the luminosity component so
this is just Y and that essentially is a
gray scale version of the image how
blight is each pixel and then we've also
got the CB and CR components so CB
represents the kind of the chrominance
the blueness of an image
so in this case some of the flower in
the middle is blue in the background is
kind of blue
but the actual flower is quite yellow
and then the CR is the redness chrome
its value
so how many is it and you can see it's
actually pretty red and the background
is not going to bed at all
so you mentioned it on so blue what
we're seeing it was great in yellow
what i've done here is i've set the
university over the image to be flat at
zero and by doing that the images in
flight and in dark and we're just only
seeing both CB and CR
so let me do a little bit of writing it
down so you can see it better
ok where we would normally have RGB
instead we have ycbcr so this is written
this way
there's lots of variations on how you
like this so we usually use this prime
symbol after the Y to represent the RGB
was gamma corrected but we won't worry
too much about that for all intents and
purposes this is the luminosity and
these are the chrominance values and
this luminosity goes between not and
255 just like RGB
the CB and CR our positions on a sort of
a square and they go for - 127 to 128 in
my mind is wandering 28 - 127
ok so that's four CB and CR and so what
we essentially have is a cube like this
where our Y goes in this direction and this
is black down here and this is white and
then our CB and CR in these directions so
this will be C our missiles ECB and
right in the center where both of these
values are 0 is gray and are gray scale
line is right down the center of this
cube and then up this direction will get
more red and then less and less red down
in this direction and off in this
direction will get more blue and down
we'll go less and less blue you see less
and less clearly more yellow in this
case yes although we call it blueness
actually also in this direction for less
blue it is in a sense the more yellow it
is similar with red the less reddit is
in general the more green it is but
these colors only start to look
realistic once you put them both back
together again and then combine them
with the luminosity component so it's in
three different color spaces and sort of
roughly have it work
while he's one of them so in general if
you had a choice you would use RGB
because it's widely supported
it's what ends up needing to be output
to a computer monitor so graphics cards
talking RGB most of the time if you're
going to print anything you're going to
have to produce into turning to CMYK
most of the print drivers will do this
for you so you don't need to worry about
that if you go into windows or any other
operating system and you print an RGB
image it will convert it to CMYK for you
and that will tell the printer how much
ink it needs to use two different colors
you would generally use ycbcr if you're
doing any kind of TV broadcasting
so if you're actually sending a stream
of data to someone's television
you need to worry about how much
compression you have about data because
it's quite important and ycbcr lets you
do very clever techniques by down
sampling the color components but not
down sampling the luminous component and
people won't really notice and we'll
talk about that when we talk about jpeg a
jpeg
in fact i should say it is fundamental
to how jpeg works is down sampling of
color components
we'd like to
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so thanks once again to harry's for
sponsoring this computer file video
jpg works by downsizing the color
components and using other techniques as
well
the majority of video compression
methods will do the same thing
so you're being compressed right now
well I certainly am yes
