4:3, 14:9, 16:9

Sorry guys - whilst the explanations of 4:3 and 16:9 have been quite good from you all - the 14:9 issue has been a bit confused - mainly because it is a different kind of aspect ratio...

When talking aspect ratios there are TWO things you need to talk about. The aspect ratio of the display you are watching on - and the aspect ratio of the active bit of the picture (i.e. the bit that isn't black bars) These can often be chosen by the broadcaster, the digital receiver box, and also the television.

This is going to hurt brains a bit !!

It is common to use the following descriptions in the broadcast industry:

12F12 This is a 4:3 full-frame picture filling a 4:3 frame

14L12 This is a 14:9 letterbox picture within a 4:3 frame
(thin black bars top and bottom)

16L12 This is a 16:9 letterbox picture within a 4:3 frame
(thick black bars top and bottom)


16F16 This is a 16:9 full-frame picture filling a 16:9 frame

14P16 This is a 14:9 pillarbox picture within a 16:9 frame
(thin black bars left and right)

12P16 This is a 4:3 pillarbox picture within a 16:9 frame
(thick black bars left and right)

The first number details the active area of the picture - the bit with real picture rather than black, the second number details the aspect ratio of the transmitted frame - i.e. the transmission format.(12 =4:3, 14=14:9, 16=16:9)

There is NO standard for broadcasting 14:9 full-frame transmitted pictures - hence they can only be either letterbox or pillarbox in 4:3 or 16:9 respectively. 14:9 is an intermediate standard really, a compromise, used especially where 4:3 and 16:9 material need to be mixed or swapped.

Some 4:3 pictures (12F12) are converted to 14:9 pillarbox (14P16) pictures for broadcast within 16:9 digital programmes - this is the case with some BBC News material, and many CBBC programmes.
Some 4:3 pictures are converted to 12:9 pillarbox (12P16) - this is the case for some sport - though in some cases the pillarbox bars are filled with image/graphics rather than black..

16:9 pictures (16F16/14P16) are often converted to 14:9 letterbox (14L12) pictures for broadcast on 4:3 analogue platforms. However other 16:9 pictures - mainly sport - are converted to 12F12 for broadcast on 4:3 analogue.

(As you can see - where 14P16 is used 14L12 is used for the 'other service' and where 12P16 is used 12F12 is used)

Digital receivers typically offer three output modes for 16:9 material. (Unfortunately the 14P16/14L12 compromises aren't used)

1. 4:3 - No Letterbox - for 4:3 tellies

This will take a 16:9 transmission - whether it be 12P16, 14P16 or 16F16 - and show the centre 4:3/12:9 portion.

4:3 (12F12/14L12 and 16L12) material will be output as broadcast.

2. 4:3 - Letterbox - for 4:3 tellies

This will take a 16:9 transmission - whether it be 12P16, 14P16 or 16F16 - and convert it to 16L12 - with big black letterbox bands top and bottom. In the case of 12P16 and 14P16 material you will also get thick or thin black lines either side.

4:3 (12F12/14L12 and 16L12) material will be output as broadcast.

3. 16:9 - for 16:9 tellies (and a few 4:3 tellies with a 16:9 mode)

This will take a 16:9 transmission - whether it be 12P16, 14P16 or 16F16 - and output it as broadcast - but will also signal via a pin on the SCART socket (and on Nokia ITVDigital receivers a line -23 - at the top of the picture) that the image is 16:9 not 4:3 - and should for the TV into WIDE mode.

4:3 (12F12/14L12 and 16L12) material will be output as broadcast - but with a signal on the SCART (line 23 on Nokia DTT receivers as well) that the image is 4:3. Widescreen TVs will then display the 4:3 image in the mode that is desired (I chose 4:3, others may chose to view in 14:9 zoom, 16:9 zoom, SMART, PANORAMA etc - but this is done by the TV set!)

When broadcasting a channel which contains both 4:3 and 16:9 transmissions - the broadcaster tags the digital video stream with headers which define the aspect ratio to allow the boxes to switch - if need be. (This is the case with Sky/DSat)

It is very complicated - but the key thing to remember is that the numbers 4:3, 14:9 and 16:9 can mean different things depending on the context.

Sounds like you've been eating too many handouts from Wood Norton noggin!

Around 90% of the reason we went digital was to dump the crappy 14:9 and go back to 4:3 again. We spend £600 in october 1998 for a new TV and were not having widescreen forced on us.

Thanks guys - I knew DTT switched automatically on receiving the aspect ratio signal, but the way some were talking at the start of this thread had me wondering whether Sky's boxes did too.

hmmm so have we got to the bottom of whether sky digi boxes can cope with widescreen signally or not? and if so why arent they using it?

when itv1 started broadcasting recently on sky digital my local itv1 station (HTV) was switching correctly and everything worked exactly like my ntl digi box.

BUT now it has all stopped and there doesnt seem to be any signalling at the moment - is my box broke or have HTV stopped sending the signalling?

Thanks mdta for those diagrams, they make a hell of a lof of sense now!

All ITV1 regions on Digital Satelite are not sending a signal at the moment, most things are broadcast in 14:9 and u can't change it till they send out a signal.