<s>
Attribute	B-Algorithm
clash	I-Algorithm
(	O
also	O
known	O
as	O
colour	B-Algorithm
clash	I-Algorithm
or	O
bleeding	O
)	O
is	O
a	O
display	B-Algorithm
artifact	I-Algorithm
caused	O
by	O
limits	O
in	O
the	O
graphics	O
circuitry	O
of	O
some	O
colour	O
8-bit	O
home	O
computers	O
,	O
most	O
notably	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
,	O
where	O
it	O
meant	O
that	O
only	O
two	O
colours	O
could	O
be	O
used	O
in	O
any	O
8×8	O
tile	O
of	O
pixels	B-Algorithm
.	O
</s>
<s>
The	O
effect	O
was	O
also	O
noticeable	O
on	O
MSX	B-Operating_System
software	O
and	O
in	O
some	O
Commodore	O
64	O
titles	O
.	O
</s>
<s>
This	O
problem	O
also	O
happens	O
with	O
the	O
"	O
semigraphic	O
modes	O
"	O
(	O
text	O
modes	O
with	O
graphics	O
features	O
)	O
of	O
the	O
Color	B-Device
Computer	I-Device
and	O
Dragon	B-Device
,	O
but	O
those	O
computers	O
also	O
have	O
non-attributed	O
graphics	O
and	O
with	O
better	O
resolution	O
.	O
</s>
<s>
Attribute	B-Algorithm
clash	I-Algorithm
on	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
was	O
caused	O
by	O
its	O
idiosyncratic	O
display	B-Algorithm
memory	I-Algorithm
layout	O
,	O
designed	O
in	O
such	O
a	O
way	O
as	O
to	O
minimise	O
memory	O
use	O
of	O
the	O
frame	B-Algorithm
buffer	I-Algorithm
,	O
and	O
optimise	O
for	O
text	O
display	O
instead	O
of	O
graphics	O
.	O
</s>
<s>
Rather	O
than	O
limit	O
the	O
colour	O
palette	O
to	O
conserve	O
memory	O
,	O
Sinclair	O
's	O
design	O
stored	O
pixel	B-Algorithm
bitmap	O
and	O
colour	O
information	O
in	O
separate	O
areas	O
of	O
memory	O
.	O
</s>
<s>
While	O
the	O
bitmap	O
specified	O
the	O
state	O
of	O
individual	O
pixels	B-Algorithm
(	O
either	O
on	O
or	O
off	O
)	O
,	O
the	O
colour	O
information	O
(	O
or	O
"	O
attributes	O
"	O
)	O
corresponded	O
to	O
the	O
text	O
character	O
matrix	O
—	O
24	O
rows	O
of	O
32	O
columns	O
—	O
with	O
one	O
byte	B-Application
per	O
8x8	O
pixel	B-Algorithm
character	O
cell	O
.	O
</s>
<s>
This	O
byte	B-Application
encoded	O
two	O
3-bit	O
values	O
,	O
known	O
as	O
INK	O
(	O
foreground	O
colour	O
)	O
and	O
PAPER	O
(	O
background	O
colour	O
)	O
after	O
the	O
BASIC	O
instructions	O
used	O
to	O
define	O
the	O
colour	O
values	O
.	O
</s>
<s>
Thus	O
,	O
each	O
8x8	O
pixel	B-Algorithm
block	O
could	O
only	O
contain	O
2	O
colours	O
from	O
the	O
15	O
available	O
,	O
which	O
must	O
both	O
be	O
from	O
either	O
the	O
BRIGHT	O
or	O
non-BRIGHT	O
halves	O
of	O
the	O
palette	O
.	O
</s>
<s>
Trying	O
to	O
add	O
a	O
third	O
colour	O
in	O
an	O
8x8	O
pixel	B-Algorithm
area	O
would	O
overwrite	O
one	O
of	O
the	O
previous	O
colours	O
.	O
</s>
<s>
The	O
ZX	B-Operating_System
Spectrum	I-Operating_System
used	O
6144	O
bytes	B-Application
for	O
the	O
bitmap	O
,	O
with	O
one	O
byte	B-Application
representing	O
eight	O
pixels	B-Algorithm
,	O
and	O
used	O
768	O
bytes	B-Application
for	O
the	O
colour	O
attributes	O
.	O
</s>
<s>
This	O
gives	O
a	O
total	O
of	O
6912	O
bytes	B-Application
for	O
the	O
entire	O
graphics	O
display	O
,	O
a	O
relatively	O
small	O
total	O
for	O
a	O
computer	O
of	O
the	O
Spectrum	O
's	O
era	O
with	O
"	O
colour	O
"	O
capabilities	O
.	O
</s>
<s>
This	O
graphics	O
architecture	B-General_Concept
was	O
retained	O
right	O
through	O
to	O
Sinclair	O
and	O
Amstrad	O
's	O
later	O
redesigns	O
of	O
the	O
Spectrum	O
,	O
up	O
until	O
Amstrad	O
's	O
final	O
model	O
,	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
+3	O
,	O
despite	O
subsequent	O
models	O
having	O
contained	O
128KiB	O
of	O
RAM	O
,	O
reducing	O
the	O
need	O
to	O
save	O
memory	O
in	O
this	O
manner	O
.	O
</s>
<s>
The	O
architecture	B-General_Concept
was	O
retained	O
to	O
prevent	O
loss	O
of	O
backward	B-General_Concept
compatibility	I-General_Concept
.	O
</s>
<s>
Attributes	O
were	O
used	O
by	O
a	O
variety	O
of	O
other	O
computers	O
and	O
consoles	O
,	O
including	O
the	O
Commodore	O
64	O
,	O
the	O
MSX	B-Operating_System
and	O
NES	O
,	O
although	O
the	O
size	O
of	O
the	O
attribute	O
blocks	O
and	O
the	O
number	O
of	O
colours	O
per	O
block	O
varied	O
.	O
</s>
<s>
However	O
,	O
with	O
the	O
use	O
of	O
hardware	O
sprites	O
,	O
attribute	B-Algorithm
clash	I-Algorithm
could	O
be	O
avoided	O
.	O
</s>
<s>
The	O
Thomson	B-Device
MO5	I-Device
and	O
TO7	B-Device
microcomputers	O
,	O
the	O
Oric	O
1	O
,	O
the	O
MSX	B-Operating_System
1	O
architecture	B-General_Concept
,	O
and	O
other	O
systems	O
based	O
on	O
the	O
Texas	B-Architecture
Instruments	I-Architecture
TMS9918	I-Architecture
video	B-General_Concept
display	I-General_Concept
controller	I-General_Concept
display	O
a	O
very	O
similar	O
constraint	O
:	O
for	O
each	O
group	O
of	O
eight	O
pixels	B-Algorithm
horizontally	O
,	O
only	O
two	O
colours	O
out	O
of	O
16	O
are	O
available	O
,	O
giving	O
a	O
similar	O
but	O
less	O
severe	O
effect	O
than	O
with	O
the	O
Spectrum	O
.	O
</s>
<s>
The	O
MSX	B-Operating_System
1	O
did	O
not	O
have	O
just	O
one	O
single	O
colour	O
attribute	O
byte	B-Application
available	O
for	O
a	O
whole	O
8x8	O
pixel	B-Algorithm
area	O
,	O
as	O
was	O
the	O
case	O
with	O
the	O
Sinclair	B-Operating_System
Spectrum	I-Operating_System
,	O
but	O
eight	O
,	O
with	O
one	O
attribute	O
byte	B-Application
for	O
each	O
8×1	O
pixel	B-Algorithm
group	O
.	O
</s>
<s>
Thus	O
,	O
while	O
the	O
Spectrum	O
was	O
limited	O
to	O
one	O
colour	O
pair	O
for	O
a	O
square	O
area	O
of	O
8x8	O
pixels	B-Algorithm
,	O
the	O
MSX	B-Operating_System
1	O
was	O
only	O
limited	O
to	O
one	O
colour	O
pair	O
for	O
a	O
"	O
line	O
"	O
of	O
eight	O
adjacent	O
pixels	B-Algorithm
.	O
</s>
<s>
In	O
addition	O
MSX1	O
could	O
use	O
sprites	O
which	O
were	O
not	O
bound	O
to	O
any	O
attribute	B-Algorithm
clash	I-Algorithm
problems	O
(	O
although	O
MSX	B-Operating_System
1	O
sprites	O
did	O
have	O
their	O
own	O
limitations	O
,	O
such	O
as	O
being	O
monochrome	O
)	O
.	O
</s>
<s>
In	O
practice	O
this	O
technical	O
advantage	O
often	O
did	O
not	O
help	O
MSX	B-Operating_System
1	O
systems	O
to	O
produce	O
better	O
pictures	O
.	O
</s>
<s>
The	O
problem	O
for	O
the	O
MSX	B-Operating_System
1	O
was	O
that	O
many	O
European	O
software	O
companies	O
who	O
converted	O
Spectrum	O
games	O
to	O
MSX	B-Operating_System
1	O
ignored	O
all	O
the	O
improvements	O
the	O
MSX	B-Operating_System
1	O
had	O
over	O
the	O
Spectrum	O
,	O
and	O
thus	O
the	O
resulting	O
MSX	B-Operating_System
1	O
versions	O
had	O
the	O
same	O
amount	O
of	O
attribute	B-Algorithm
clash	I-Algorithm
as	O
the	O
original	O
Spectrum	O
games	O
(	O
Jack	B-Application
the	I-Application
Nipper	I-Application
II	I-Application
:	I-Application
In	I-Application
Coconut	I-Application
Capers	I-Application
is	O
one	O
example	O
of	O
this	O
)	O
.	O
</s>
<s>
To	O
ease	O
conversion	O
,	O
the	O
software	O
developers	O
simply	O
copied	O
the	O
single	O
attribute	O
byte	B-Application
value	O
of	O
the	O
Spectrum	O
to	O
all	O
eight	O
corresponding	O
attribute	O
bytes	B-Application
of	O
the	O
MSX	B-Operating_System
1	O
.	O
</s>
<s>
For	O
the	O
same	O
reason	O
,	O
the	O
software	O
companies	O
also	O
ignored	O
the	O
sprite	O
capabilities	O
of	O
the	O
MSX	B-Operating_System
1	O
,	O
and	O
because	O
the	O
video	O
display	O
capabilities	O
were	O
otherwise	O
quite	O
similar	O
(	O
256×192	O
resolution	O
,	O
16	O
colours	O
)	O
,	O
both	O
systems	O
produced	O
virtually	O
identical	O
displays	O
for	O
the	O
same	O
game	O
.	O
</s>
<s>
In	O
contrast	O
,	O
Japanese	O
MSX	B-Operating_System
1	O
games	O
did	O
use	O
all	O
the	O
capabilities	O
of	O
MSX	B-Operating_System
1	O
,	O
often	O
resulting	O
in	O
better	O
looking	O
games	O
.	O
</s>
<s>
To	O
avoid	O
attribute	B-Algorithm
clash	I-Algorithm
,	O
static	O
graphic	O
displays	O
had	O
to	O
be	O
constructed	O
with	O
care	O
.	O
</s>
<s>
Finely-detailed	O
colour	O
graphics	O
were	O
impossible	O
,	O
as	O
colour	O
could	O
only	O
be	O
applied	O
in	O
8×8	O
pixel	B-Algorithm
blocks	O
.	O
</s>
<s>
If	O
just	O
one	O
pixel	B-Algorithm
in	O
an	O
8×8	O
block	O
was	O
recoloured	O
because	O
a	O
moving	O
part	O
of	O
the	O
display	O
touched	O
it	O
,	O
the	O
entire	O
block	O
would	O
change	O
colour	O
.	O
</s>
<s>
This	O
also	O
made	O
graphics	O
faster	O
,	O
as	O
less	O
of	O
the	O
screen	O
had	O
to	O
be	O
updated	O
—	O
both	O
a	O
smaller	O
region	O
,	O
plus	O
only	O
changing	O
pixel	B-Algorithm
information	O
and	O
leaving	O
the	O
colour	O
area	O
untouched	O
.	O
</s>
<s>
Some	O
Spectrum	O
software	O
,	O
such	O
as	O
FTL	O
's	O
Light	B-Application
Force	I-Application
,	O
used	O
extremely	O
careful	O
graphics	O
design	O
to	O
achieve	O
full-colour	O
moving	O
graphics	O
,	O
essentially	O
by	O
limiting	O
both	O
the	O
design	O
of	O
the	O
onscreen	O
elements	O
and	O
their	O
paths	O
of	O
motion	O
to	O
8×8	O
colour	O
resolution	O
boundaries	O
.	O
</s>
<s>
No	O
mainstream	O
developers	O
were	O
able	O
to	O
find	O
a	O
suitable	O
all-round	O
fix	O
for	O
the	O
attribute	B-Algorithm
clash	I-Algorithm
problem	O
,	O
instead	O
preferring	O
to	O
use	O
the	O
monochrome	O
graphics	O
method	O
when	O
fast	O
,	O
clear	O
graphics	O
were	O
needed	O
,	O
and	O
full-colour	O
graphics	O
when	O
the	O
situation	O
permitted	O
.	O
</s>
<s>
Most	O
games	O
before	O
1987	O
ignored	O
attribute	B-Algorithm
clash	I-Algorithm
.	O
</s>
<s>
Some	O
later	O
games	O
,	O
such	O
as	O
Knight	B-Application
Tyme	I-Application
and	O
Three	B-Application
Weeks	I-Application
in	I-Application
Paradise	I-Application
allowed	O
players	O
to	O
select	O
between	O
two	O
modes	O
of	O
attribute	B-Algorithm
clash	I-Algorithm
:	O
one	O
which	O
ignored	O
main	O
character	O
attributes	O
,	O
blending	O
the	O
character	O
into	O
the	O
background	O
and	O
vice	O
versa	O
,	O
prioritising	O
the	O
characters	O
colour	O
scheme	O
over	O
the	O
background	O
imagery	O
.	O
</s>
<s>
Another	O
workaround	O
was	O
to	O
simply	O
render	O
the	O
graphics	O
in	O
two	O
colours	O
,	O
otherwise	O
known	O
as	O
monochrome	O
,	O
as	O
done	O
with	O
the	O
Spectrum	O
version	O
of	O
Knight	B-Application
Lore	I-Application
in	O
1984	O
.	O
</s>
<s>
Many	O
games	O
used	O
full-colour	O
backgrounds	O
and	O
"	O
character	O
scrolling	O
"	O
(	O
where	O
the	O
environment	O
was	O
scrolled	O
eight	O
pixels	B-Algorithm
at	O
a	O
time	O
)	O
,	O
but	O
monochrome	O
sprites	O
that	O
were	O
effectively	O
transparent	O
,	O
as	O
in	O
Double	B-Application
Dragon	I-Application
,	O
were	O
drawn	O
in	O
such	O
a	O
way	O
so	O
they	O
stand	O
out	O
,	O
avoiding	O
dependence	O
on	O
colour	O
.	O
</s>
<s>
Many	O
games	O
used	O
this	O
method	O
with	O
smooth	O
pixel-by-pixel	O
scrolling	O
,	O
but	O
the	O
attribute	B-Algorithm
clash	I-Algorithm
as	O
elements	O
of	O
one	O
character	O
block	O
were	O
"	O
passed	O
"	O
to	O
the	O
next	O
were	O
clearly	O
visible	O
.	O
</s>
<s>
A	O
prominent	O
(	O
and	O
less	O
successful	O
)	O
example	O
of	O
the	O
use	O
of	O
full-colour	O
graphics	O
was	O
the	O
Spectrum	O
conversion	O
of	O
Altered	B-Application
Beast	I-Application
.	O
</s>
<s>
The	O
game	O
suffers	O
from	O
considerable	O
attribute	B-Algorithm
clash	I-Algorithm
.	O
</s>
<s>
Games	O
that	O
used	O
this	O
technique	O
included	O
Popeye	O
,	O
The	B-Application
Trap	I-Application
Door	I-Application
,	O
Through	O
the	O
Trapdoor	O
,	O
and	O
Flunky	B-Application
.	O
</s>
<s>
Other	O
developers	O
who	O
used	O
a	O
similar	O
technique	O
included	O
Mike	O
Singleton	O
,	O
with	O
Dark	B-Application
Sceptre	I-Application
,	O
and	O
Gang	O
of	O
Five	O
,	O
with	O
Dan	B-Application
Dare	I-Application
:	I-Application
Pilot	I-Application
of	I-Application
the	I-Application
Future	I-Application
.	O
</s>
<s>
In	O
1994	O
,	O
programmer	O
Igor	O
Maznitsa	O
developed	O
a	O
multi-CPU	O
concept	O
platform	O
"	O
ZX-Poly	O
"	O
based	O
on	O
ZX-Spectrum-128	O
;	O
the	O
platform	O
allows	O
for	O
avoidance	O
of	O
attribute	B-Algorithm
clash	I-Algorithm
,	O
and	O
can	O
even	O
colourise	O
many	O
old	O
games	O
without	O
changes	O
in	O
executable	O
code	O
.	O
</s>
