Written by Gordon Fraser,
posted with permission from:
http://www.convergent-av.co.uk/article4.html
Note: originally written for PAL, but also quite relevant for NTSC.
----------------------------
Scalers: Many folk seem confused as to what scalers actually are. The common belief is that they just de-interlace SD material and then rescale it to some other resolution. Indeed when discussing scalers often the comments are usually about what de-interlacing chipset is used above anything else. It's true that those are main features of scalers but there is more to it than that. How they go about these tasks matter, as do some of the other features a scaler can have that may offer increases in performance over in built video processing. Here's some of the things we believe scalers should do.
Scalers are the glue that binds together a video system. Modern displays are not able to display our old and new television standards without some form of processing being involved. Most of our video systems at home will have a large and disparate range of sources with varying output resolutions and refresh rates. None of these sources are likely to actually output a resolution or refresh rate that is optimum for our display! Good scalers are able to be configured to optimise the capture and processing of all these signals and to then output them at the most appropriate resolution and refresh rate for the source material and the display. Here are some examples:
Sources:
Satellite TV: 576i usually by SCART or svideo
VCR: PAL, Composite video
DVD: Region1, 480i@60Hz via Component or possibly HDMI
DVD: Region2, 576i@50Hz via Component or possibly HDMI
ProgDVD: R1, 480P@60Hz via Component, HDMI or DVI
ProgDVD: R2, 576P@50Hz via Component, HDMI or DVI
HD Tape: 1080i@60Hz via Component or HDMI
HD Satellite: 1080i@50Hz or 720P@50Hz via component or DVI HDCP/HDMI
Displays:
SD plasma's... and clones : 852x480
HD 42" plasma... : 1024x768
50" plasma and clones : 1366x768
Alis panels and clones : 1024x1024
Pioneer 43" plasma: 1024x768
Pioneer 50" plasma : 1280x768
DLP: 1280x720 or 1024 x576
DILA: 1365x1024 or 1400x800 or 1920x1080
SXRD : 1920x1080
LCD : 1280x720, 1920x1080, 1366x768
CRT Front Projection : Variable from 480P up to 1080P or more!
If you compare the source output resolutions with the displays actual resolutions you can see why we need scalers.
Standard definition signals in composite, s-video, component or SCART (RGBcvS) should be able to be processed alongside HDMI, DVI, RGBHV, or High Definition component. These analogue signals should be sampled at a very high rate in order to get good, accurate information to the front end of the system. The Digital inputs meanwhile should be capable of accepting the full range of signals available from current sources from 480i up to 1080i.
Advanced greyscale, gamma and colour decoding combined with careful adjustment of input sizing should allow for each source to be optimised for the most accurate and detailed playback. Over-scanning of the incoming signals can be minimised and active picture area being sent to the display should be adjustable to allow the full picture resolution to be displayed on screen. Digital video levels on input and output should be selectable for PC or VIDEO dependant on source as required in order to gain maximum contrast with minimal banding artefacts.
Multiple inputs should allow direct connection of each source to the scaler, removing the need for switching of video elsewhere which could degrade the signal quality and which would mean many components would have to share the same input (compromising one or all of their picture quality).
Advanced powerful detection algorithms should work out whether the video material is from original progressive content (film or PC graphics) or from interlaced video cameras and appropriate processing then should take place. Original progressive images should be re-constituted to their full resolution frames then sent on to be up or downscaled to the required resolution of the display. Accurate frame rate conversion should then be able to output the progressive frames at the most appropriate rate eliminating judder and other temporal artefacts. Clever filtering should be employed to remove harsh digital artefacts like mosquito noise, where appropriate. Chroma filtering should be assignable on a per source basis for digital sources with mpeg decoders that suffer from the famous, chroma bug.
Fast processing and as little buffering of the video signal as possible should be applied in order to minimise potential lip-sync errors that may require the use of expensive audio delays. This processing should be able to be updated to add further feature sets or to aid product compatibility.
If possible multiple memories should be available to allow quick and simple adjustments for more than one display or perhaps for day and night-time viewing. The unit, once set up, should be extremely simple to use.
Advanced RGB gamma and overall LUMA adjustments may be available on a per input and memory basis. This would allow ISF calibrators to make very accurate adjustments for greyscale where the capability wasn't present in the display or where non linear tracking after calibration required further tweaking.
As we have a mixture of analogue and digital displays still it'd be wise for the scaler to have analogue outputs that could be configured for RGB or YPrPb output, preferably on high quality 75ohm BNC connectors where high resolution displays are going to be used. For digital displays DVI-D or HDMI outputs should be available. The output resolution and timing parameters of the scaler should be adjustable in order to create the perfect timings required to minimise artefacts on screen. In built test patterns should be available to help in set up and confirmation of ideal scaler/display configuration.
With the advent of High Definition broadcasts about to start in the UK we'd expect that high definition inputs should be available. These inputs should not just pass through an HD signal. There are many displays that are not compatible with either the resolutions or the refresh rates of HD broadcasts. Good video processing should be able to capture these HD signals and frame rate convert them and scale to allow compatibility with older displays.
posted with permission from:
http://www.convergent-av.co.uk/article4.html
Note: originally written for PAL, but also quite relevant for NTSC.
----------------------------
Scalers: Many folk seem confused as to what scalers actually are. The common belief is that they just de-interlace SD material and then rescale it to some other resolution. Indeed when discussing scalers often the comments are usually about what de-interlacing chipset is used above anything else. It's true that those are main features of scalers but there is more to it than that. How they go about these tasks matter, as do some of the other features a scaler can have that may offer increases in performance over in built video processing. Here's some of the things we believe scalers should do.
Scalers are the glue that binds together a video system. Modern displays are not able to display our old and new television standards without some form of processing being involved. Most of our video systems at home will have a large and disparate range of sources with varying output resolutions and refresh rates. None of these sources are likely to actually output a resolution or refresh rate that is optimum for our display! Good scalers are able to be configured to optimise the capture and processing of all these signals and to then output them at the most appropriate resolution and refresh rate for the source material and the display. Here are some examples:
Sources:
Satellite TV: 576i usually by SCART or svideo
VCR: PAL, Composite video
DVD: Region1, 480i@60Hz via Component or possibly HDMI
DVD: Region2, 576i@50Hz via Component or possibly HDMI
ProgDVD: R1, 480P@60Hz via Component, HDMI or DVI
ProgDVD: R2, 576P@50Hz via Component, HDMI or DVI
HD Tape: 1080i@60Hz via Component or HDMI
HD Satellite: 1080i@50Hz or 720P@50Hz via component or DVI HDCP/HDMI
Displays:
SD plasma's... and clones : 852x480
HD 42" plasma... : 1024x768
50" plasma and clones : 1366x768
Alis panels and clones : 1024x1024
Pioneer 43" plasma: 1024x768
Pioneer 50" plasma : 1280x768
DLP: 1280x720 or 1024 x576
DILA: 1365x1024 or 1400x800 or 1920x1080
SXRD : 1920x1080
LCD : 1280x720, 1920x1080, 1366x768
CRT Front Projection : Variable from 480P up to 1080P or more!
If you compare the source output resolutions with the displays actual resolutions you can see why we need scalers.
Standard definition signals in composite, s-video, component or SCART (RGBcvS) should be able to be processed alongside HDMI, DVI, RGBHV, or High Definition component. These analogue signals should be sampled at a very high rate in order to get good, accurate information to the front end of the system. The Digital inputs meanwhile should be capable of accepting the full range of signals available from current sources from 480i up to 1080i.
Advanced greyscale, gamma and colour decoding combined with careful adjustment of input sizing should allow for each source to be optimised for the most accurate and detailed playback. Over-scanning of the incoming signals can be minimised and active picture area being sent to the display should be adjustable to allow the full picture resolution to be displayed on screen. Digital video levels on input and output should be selectable for PC or VIDEO dependant on source as required in order to gain maximum contrast with minimal banding artefacts.
Multiple inputs should allow direct connection of each source to the scaler, removing the need for switching of video elsewhere which could degrade the signal quality and which would mean many components would have to share the same input (compromising one or all of their picture quality).
Advanced powerful detection algorithms should work out whether the video material is from original progressive content (film or PC graphics) or from interlaced video cameras and appropriate processing then should take place. Original progressive images should be re-constituted to their full resolution frames then sent on to be up or downscaled to the required resolution of the display. Accurate frame rate conversion should then be able to output the progressive frames at the most appropriate rate eliminating judder and other temporal artefacts. Clever filtering should be employed to remove harsh digital artefacts like mosquito noise, where appropriate. Chroma filtering should be assignable on a per source basis for digital sources with mpeg decoders that suffer from the famous, chroma bug.
Fast processing and as little buffering of the video signal as possible should be applied in order to minimise potential lip-sync errors that may require the use of expensive audio delays. This processing should be able to be updated to add further feature sets or to aid product compatibility.
If possible multiple memories should be available to allow quick and simple adjustments for more than one display or perhaps for day and night-time viewing. The unit, once set up, should be extremely simple to use.
Advanced RGB gamma and overall LUMA adjustments may be available on a per input and memory basis. This would allow ISF calibrators to make very accurate adjustments for greyscale where the capability wasn't present in the display or where non linear tracking after calibration required further tweaking.
As we have a mixture of analogue and digital displays still it'd be wise for the scaler to have analogue outputs that could be configured for RGB or YPrPb output, preferably on high quality 75ohm BNC connectors where high resolution displays are going to be used. For digital displays DVI-D or HDMI outputs should be available. The output resolution and timing parameters of the scaler should be adjustable in order to create the perfect timings required to minimise artefacts on screen. In built test patterns should be available to help in set up and confirmation of ideal scaler/display configuration.
With the advent of High Definition broadcasts about to start in the UK we'd expect that high definition inputs should be available. These inputs should not just pass through an HD signal. There are many displays that are not compatible with either the resolutions or the refresh rates of HD broadcasts. Good video processing should be able to capture these HD signals and frame rate convert them and scale to allow compatibility with older displays.
