
English: 
For most of us today, television static is
a thing of the past.
With digital tuners, HDMI connections and
flat screen TVs, even if there is interference,
we don't get a chance to see it, as the television
circuity boldly saves us from this ordeal.
Early TVs adopting digital tuners would actually
spoof this snowy noise themselves, so as not
to disturb people, but otherwise we get a
blank screen, maybe a message hovering about,
politely informing us of the lack in coherent
signal.
Thankfully the message never, ever, directly
hits the corner.
If it did, well, I hate to imagine the consequences....

Chinese: 
对于我们今天大多数人来说，电视雪花已经是过去式了
在数字解调电视、HDMI连接和液晶电视时代，即使遇到干扰
我们也没有机会看到电视雪花了，因为电视的电路已经帮我们挡住了它
早期使用数字解调的电视会屏蔽掉吵人白噪声
同时电视上会显示一个空白画面或者一个跳来跳去的“NO SIGNAL”
提示我们电视信号已经中断
幸好这个消息遇到边框会弹回来
不然可能……会有这种情况……

English: 
*EXPLOSION*
But people like me, and probably you, still
have to deal with garbled screens of static
on a regular basis, especially for older consoles
which only provide an RF output, and even
then, it's non uncommon to get quite a noisy
picture.
But given we're using colour TVs for the most
part, producing a colour image, why on earth
is the TV static only black and white?
Well, let's start with fundamentals.
Why do we even get this static fuzz?
Well analogue televisions try to amplify any
signals they receive, so if there isn't a
strong enough signal from a TV mast, or a
modulator being sent into the TVs receiver

Chinese: 
还行*BOOM*
不过像我或是你依然有机会看到电视出现雪花
尤其是一些只有射频输出的老机器的时候
那么看到电视雪花也并不少见了
不过我们大多用彩色电视，提供彩色图像
那么究竟为何电视雪花仍然是黑白的呢？
我们先介绍一些原理
来解释为何会看到雪花状的图像
模拟电视会放大任何接收到的信号
如果电视信号不够强，或者电视的解调器没有正确选在频道上

English: 
at the frequency it's currently tuned to,
it will instead amplify whatever electromagnetic
signals it picks up.
These signals can originate from a number
of sources including residual signals spilling
over from the big bang - cosmic microwave
background radiation, man made signals buzzing
around the air, atmospheric sources, but mainly,
it's Johnson noise (not that kind).... essentially
thermal RF noise generated by the components
of the TV itself.
Because of the random nature of these signals,
your television receiver interprets it as
as a garbled fuzz of noise, presented as a
swarm of seemingly frantic ants on screen.
If it wasn't random you'd perceive patterns
in this dissaray, and of course an ordered,
stronger signal would pretty much cancel out
this noise altogether and present us with
a coherent image.
The reason the colour of this snow isn't as
random as the patterns themselves is due to

Chinese: 
它依然会如实放大接收到的信号
这些信号来源多种多样
包括宇宙大爆炸 - 3K背景辐射，
空中人为的信号，不过主要的来源是器件的Johnson noise（大雾）
事实上是器件本身产生的热噪声
正因为这些随机输入的信号，你的电视才将其转化为
乱七八糟的噪声，看起来就像一窝乱跑的蚂蚁
如果信号并非随机的，你会发现图像会变得错位
那是因为强一些的、规则的信号可以盖过去这些噪声
让电视显示这些图像
而雪花的颜色并不像图像本身那样随机

English: 
the way televisions and transmissions have
evolved.
Let's look at segment from a PAL video signal.
From left we have the end of a video scan
line.
This constitutes a single line drawn across
your television by an electron gun (on cathode
ray tube televisions at the least).
We then have the front porch, this is here
to prevent interference between individual
lines.
Next is the horizontal sync pulse, which signifies
the start of the next scan line.
This is followed by the back porch, which
restores the black levels and also leads onto
the colour burst.
Now this is the important part, as it effectively
tells our television how to create the colour
image.
The colourburst synchronises a subcarrier
signal containing the colour data.
The encoded format of which relies on the
YUV colour space, providing chrominance data
to go with the luminance value.

Chinese: 
这是电视和图像传输方式决定的
这里会展示PAL电视信号的组成
左面这里我们会看到一行的尽头
代表电子枪在电视上扫过的一条线
（在CRT电视或者至少是个电视）
这里有一个消隐前肩，为了防止行之间干扰
 
然后这里是一个行消隐脉冲，代表下一行扫描线的开始
接着是一个消隐后肩，用来指示黑电平（消隐电平）
同时提供色同步信号
色同步是一个重要部分，它将告诉电视如何还原颜色
 
色同步信号可以同步包含颜色信息色度副载波信号（即包括相位和频率）
颜色编码依赖于YUV色彩空间
提供色度向亮度的转化

Chinese: 
色度数据包括红蓝两部分值
从亮度中和红蓝值做差即可得到绿色值
由于单色电视依靠信号中的亮度数据来指示图像每部分的亮度
在每个扫描线之外提供颜色信息（这里说法不严密，色度信号是调制在亮度信号之上的，所以称之为副载波）
而黑白电视会忽略色度信息
这也保证了黑白格式和彩色格式的兼容
与使用RGB需要传输三个信号相比
它只需要更少的带宽
彩色副载波通过一条扫描线上只提供一半的垂直分辨率
来进一步降低占用带宽
但是我们不会感觉到有严重失真，因为相比颜色
我们的眼睛对亮度更敏感
结果就是，除非你的电视能接收并正确解调到信息，
不然都是以黑白模式工作

English: 
The chrominance data carries blue and red
values, which are substracted from the luminance
figure to provide a value for green.
Given that monochrome televisions rely on
the embedded luminance data to identify how
bright each part of the image is, delivering
colour information outside of each visible
scanline, ensured compatibility with monochrome
TV receivers, which simply ignored it - an
essential caveat during its introduction.
It also required far less bandwidth than using
3 separate signals to transmit Red, Green
and Blue components.
The colour subcarrier itself reduces bandwidth
further by only providing half the vertical
resolution on every other scan line.
We don't perceive any different as our eyes
see a constrasting monochrome image in more
detail than a colour one.
But the upshot is, until your TV receives
and recognises this information, it's essentially
running in Black & White mode.

Chinese: 
每次扫过一条扫描线时，电视会试着找出并不存在的色同步信号
然后继续重复之前的操作
随机信号里没有可以用来重放彩色的信息
所以尽管你可能希望在随机信号/条纹被电视解调为
一大把五彩斑斓的颜色
它们仅仅是不能以电视可以解码成彩色信息的方式传送
这种条件下，电视仍然是认为60年代的
黑白电视信号进了屋子
那么声音又是怎样一回事呢？
在一个无正确信号输入的电视中，声音信号像视频信号一样都是随机的
也就将随机信号放大了
在正确信号的频道内，声音信号在视频信号的一个固定频偏上
这也是为何你有时能正确看到图像
然而还是没有声音

English: 
Each time it draws a line, it looks for the
subsequent colourburst pattern, but doesn't
find it, and moves on.
It hasn't been given the information to create
a colour image.
So although you may expect the random signals
& fluctuations received & displayed on an
untuned television to be interpreted as a
multitude of different colours, they're simply
not delivered in a fashion which the TV can
decode into colour information.
At this point, the decoder is really still
expecting a 1960s B&W film to be streamed
into living rooms.
So, what about the sound?
Well, in an untuned set, the sound is as random
as the on screen image, with the set amplifying
all those floating no good signals.
With a tuned channel, the sound data is held
on a frequency with a fixed off-set.
This is why even if you can sometimes tune
into a picture spilling over from its broadcast
frequency, it may may still have no sound.

Chinese: 
直到调节正确，频偏在声音数据上的时候
电视才能重放声音
这里说一下PAL格式。虽然电视制式和电视制式有一点不同
但原理也是相通的
比如说NTSC制式，工作原理几乎相同，但是在色度副载波频率上
有一些不同
这也就是为何在玩NTSC游戏(在PAL电视上)的时候只能看到黑白图像的原因
电视看到不认识的色度副载波时不知所措
在法国，SECAM制式将色度信号通过FM调制在信号中，而不是是通过色度副载波和色同步
来提供色度信息
不管怎样，不论在哪，设备在回放图像到我们的眼睛之前
接收器都需要找到合适的色彩信息
这也就是电视雪花是黑白的原因

English: 
The receiver won't find the sound data until
the picture is tuned to the correct frequency
and the off-set is matched up.
Now, I've been talking about the PAL system
here and although there are small differences
from TV protocol to TV protocol, the reason
is very much the same.
NTSC for example, works on an almost identical
principle, but with a different colour subcarrier
frequency.
This is why when we play an NTSC game or video
over here, we get a black and white image....
again, the TV has no idea on what colours
to paint over the image.
Over in France, their SECAM protocal encoded
colour signals in FM rather than relying on
a colourburst sync.
But regardless, where-ever in look, the decoders
need to be able to find suitable colour information

English: 
to decode, before it can be presented to our
eyes.
