Video Processors - other features within your processor

Noise reduction

Asides from deinterlacing and scaling, and doing these processes well, there is still more to generating the ultimate picture. Noise (or “grain”) is something that will plague all images and can be picked up through broadcast, cabling, disc error, pick up, or even in the recording studio. The simplest filtering used (and used quite commonly) is to simply filter out every instance of a single, seemingly random pixel (or pair of pixels). This is known as “spatial filtering” and is based on the theory that information in the picture is not likely to be just one pixel in size. Unfortunately this technique often removes detail too, so the image while apparently free from unwanted noise, is also quite “soft”. Skin tones may not look right where tiny blemishes have simply been taken out of the image.

A “temporal filter” might analyse a questionable pixel in the various fields before it in time, should it only appear in one frame then it might be noise and will be ignored, if repeated then it is more likely to be detail. This has very good results and is a technique often only found in the better after-market processors and higher end displays. However that pixel of noise might also be a part of a moving object within the image. As with deinterlacing, the ideal would be to carry out a (per-pixel) motion adaptive temporal filter to analyse those pixels for motion, as well as existence over time. The deepest analysis (and of higher resolution images) involves massive processing power, so a full per-pixel, motion-adaptive, noise-adaptive, temporal filter is reserved for only the highest power processors. Especially for HDTV resolutions.

Detail Enhancement

Detail enhancement is another area of improvement. Initially all digitised signals are filtered to prevent inaccuracies such as false colour or moiré effects. This is known as anti-aliasing which has the unfortunate effect of having to blur some detail. To combat this, edge-enhancement is employed to sharpen these blurred areas. It works on the theory that the human brain perceives sharpness as the contrast between dark and light. Surrounding an object with a white edge therefore makes it appear sharper to the eye, however done without any grace and it will simply look like an object with a white line around it!! This artefact is known as “ringing” or “haloing” and is a common side-effect of poor edge-enhancement. Unfortunately this might already be inherent in your signal if edge-enhancement has been applied in the studio…

A better processor will use an analysis step to identify the more blurred areas of the image and then only apply edge-enhancement here, perhaps more conservatively than the brute-force technique a simpler processor might use. When combined with the analytical steps in the scaling process the results will be true to the original.

Gamma and Luma adjustment

Many processors will include adjustment for the RGB Gamma and overall Luma of the image. This enables the system calibrator to make precise adjustment to grayscales and colour accuracy, for the final image to not only be faithful in terms of detail and sharpness, but in terms of colour and varying black levels too.

Functional and Operating Tools

As you may have used with your existing TV, there will be a selection of different memories or modes to select depending on what you are displaying. You might select a “game” mode when using game consoles which have a duller output than your other video sources. A more advanced processor will allow the various adjustments and settings for colour and grayscales, edge-enhancement, noise reduction, ultimate output resolution even, to be configured differently for each individual input. You might have multiple output memories for both day and night use where differing ambient light levels will require different grayscale characteristics. Or more commonly you might have a projector and a plasma screen being driven by your processor, so for all the various inputs these would require a double set of output settings, each tailored to either the projector or plasma screen.