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Question 2 How
many colours can be represented in the RGB system?
Check your answer
The settings of your computer, your type of monitor and
video adapter determine the maximum number of colours
that can be displayed. If a colour can not be represented
then the nearest available colour will be used. How this
can be done is described in the next section.
Dithering
Depending on the computer system being used and how it
is set up will depend on how many colours can be displayed.
If the computer is set to 256 colours then only 256 colours
can be displayed. The computer may try to simulate additional
colours by dithering. This is a process where different
colours are displayed on adjacent pixels in a chess board
pattern. If we coloured the chess board with black and
white squares then reduce the size of the board so that
each square consists of a single pixel, then because the
pixels are very small, this check board pattern gives
the impression of a medium grey. Looking very closely
at screen the pattern can be seen. Looking normally the
eye blends the pattern into, in this case medium grey.
This does not look as pleasing as a screen that displays
all the pixels as medium grey.
A different pattern could have say 2 black pixels to
every white one, producing the effect of a darker grey.
This patterning is very similar to how a TV screen works.
Look at the screen through a reversed pair of binoculars
with the eye piece held against the screen to see the
individual red green and blue sectors. Look at a white
area of the screen for the best effect where all 3 colours
are at there brightest.
Most modern computers, with there improved memory, and
hardware, can usually display in 32 bit true color, that
does not require dithering.
Safe Colours
Out of 16.7 possible colours, there is a list of only
216 web safe colours that should give the same true colour
on PCs and almost the same colour on Macs.
Starting at 0 the values are increased by 51 denary to
255. You may wonder why a strange number like 51 is used.
If you calculate it out then 51 is 20% of 255.
Converting 51 denary, to hexadecimal you get 33 hex,
so the values are increased from 00 by 33 hexadecimal
to FF). Learn more about hexadecimal
numbers
This allows combinations of the following hexadecimal
numbers.
00, 33, 66, 99, CC, FF.
Safe
Colour Chart. This very neat chart has been produced
by Jim Taylor, another student in the same Tutor Group
of the Open University as myself.
Question 3 From
this list of 6 allowable numbers, how do we work out the
total number of web save colours?
Check your answer
If you do not want strange colours or dithered colour
patterns stick to these safe colours for your web page,
text, background and graphic colours.
Question 4.
Test you grasp of the RGB theory and attempt to place
the following safe RGB values
#006633, #66FFFF, #FFFF99, #990000, #999999, #9933FF
to the Samples 1 to 6. The colours are sufficiently different
for you to do this accurately. Looking at the Colour
Wheel diagram should help.
Check your answer |