Crystal Vision
Aspect Ratio
Correction
6 Aspect Ratio Correction
Wallbox Q-Down
has the ability to deal with any HD to SD aspect ratio conversion
requirements. You can select a 16:9 Anamorphic output for 16:9 SD systems and either a
16:9 to 4:3 Letterbox, 16:9 to 4:3 Letterbox compromise, or 16:9 to 4:3 Full Screen with centre
cut for 4:3 SD systems.
Wallbox Q-Down
also allows you to customise the shape of your output picture. Each of the
standard aspect ratios can be individually adjusted away from the default values to create
customised versions by using four independent sets of size, position and crop controls.
Wallbox Q-Down
ensures the picture is always the right shape by coping with both analogue
and digital SD blanking widths – particularly useful for feeds that are up and down converted
multiple times. When used with an Anamorphic conversion, the ‘SD Analogue Line Length’
option puts the active 1920 pixels from a 1080i or 1080p picture into 702 pixels of SD (rather
than 720 pixels), with the rest of the pixels used to represent analogue blanking – which
prevents the SD signal from losing the sides of the picture. All other aspect ratios are adjusted
by a similar amount.
Wallbox Q-Down
can automatically choose the appropriate aspect ratio according to the
SMPTE 2016 AFD data embedded in the 3Gb/s or HD input video. HD programmes are often
made of a mixture of true High Definition sources and SD-originated sources that have been
up converted, and the SMPTE 2016 AFD code in the signal gives information about which
areas of the screen contain a picture and which areas have black ‘padding’. The down
converter needs to read this signal and select the correct aspect ratio conversion to be used
with the down conversion.
Wallbox Q-Down
offers three options for the SD output. In
Auto 16:9 mode
the SD outputs
can be set to be always 16:9 and in this case it will perform the down conversion without ever
changing the aspect ratio. In
Auto 4:3 mode
the SD outputs can be set to be always 4:3, in
which case it will down convert and perform either a Letterbox or centre cut, depending on the
source material. In
Auto Adaptive mode,
if the HD input is 16:9 full frame the picture is down
converted with no aspect ratio conversion and is output as 16:9 SD. If the SMPTE 2016 data
indicates that the HD input is a 16:9 Pillarbox, however, a centre cut is performed and the
output is 4:3 SD.
Although it would normally be a requirement for an automatic system to label all the 3Gb/s or
HD video images to show their format and control the down converter, with
Wallbox Q-Down
it is only necessary to label those that are not full frame 16:9 images. When the input is not
labelled the down converter uses its default assumption that an HD image is a full frame 16:9.
It is therefore possible to have a powerful system with the majority of signals not containing
SMPTE 2016 information.
6.1 Fixed Aspect Ratios
There are four fixed aspect ratios which are Anamorphic, 16:9 Letterbox, 14:9 Letterbox and
Centre Cut. Anamorphic will map the input picture directly to the native aspect ratio of the
viewing display along with the resulting distortion associated with this. Should it be necessary
to view the output on a 4:3 display, setting the aspect ratio selection to Letterbox will give the
correct picture dimensions by adding black bars to the top and bottom of the picture.
Selecting 14:9 Letterbox will crop the picture to 87.5%, and depending on the aspect ratio of
Wallbox Q-Down User Manual R1.0
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08 August 2016