First of all it’s important to outline what a digital scaler is, because it’s inappropriate to assume that everyone is familiar with the fundamentals.

Practically all of today’s display devices have some sort of on-board scaling chip for handling the range of signals being sent to them. The scaler’s function is to ensure that the image coming in – if not exactly complying with the device’s native format and resolution – will display correctly.

Some scaling chips are of questionable quality and it’s best to use an external scaling device where possible. However, considering the quality of many new LCDs, LEDs, OLEDs and other panel types, this is not as simple a matter as it was a few years back. There is still a catch, as will be mentioned later.

To use the analogy of a water pipe with a flow reduction in it: a scaler is like having a thin stream of water in a 15mm pipe opening up into a 100mm pipe. You won’t get 100mm worth of water from the outlet, because there isn’t enough going in, but there will be a much easier flow.

This may be a simplistic way of looking at it, but it does help in understanding the implications for bandwidth when it comes to scaling.

One could say the scaler is a tool for increasing the resolution (therefore bandwidth) of a video signal, but there’s a bit more to it than that.

Modern scalers are complex devices able to stabilise images, change aspect ratios, provide digital noise filtering and artefact reduction while changing one resolution to another – among other capabilities.

Typically, the most complex task is to take a low-resolution image such as a composite video signal from a receiver box and scale it to a ‘Full HD’ image. For a start, there is much less resolution to deal with, artefacts from compression applied by the broadcaster, frame-rate differences, etc.

However, external scalers – as found in presentation switchers, range extender receivers and some matrix switchers – are in most cases used for managing the myriad graphics card resolutions present in corporate AV installations.

To understand the implications of this, we have to touch on the matter of EDID, an acronym that is key to making HDMI signals work. Extended display identification data is simply the display device telling the source what it wants to receive.

Simple? Yes, if you are only connecting a Blu-ray player to a LCD display. Not so simple if you have multitudes of computers with HDMI, DisplayPort and VGA all wanting to output different resolutions. Throw in other sources, such as cameras or DVD, and there’s a good chance of a mess.

This is where external scaling comes into its own. Display resolutions in a typical AV installation can range from 1024×768 to 1920×1080 (‘Full HD’), or even 2K and now 4K (a little more on that later).

Perhaps it is best to explain EDID, HDMI, VGA – and why not throw in HDCP while I am at it – by way of an example.

Let’s say a typical boardroom system has an LCD ‘Full HD’ panel on the wall, a projector with a native resolution of 1280×800 and, in a remote location (via range extenders), two more monitors with resolutions of 1680×1050.

The good thing is that there aren’t any 4×3 aspect ratios to deal with; the bad is that native resolutions are all over the place and we are faced with a mix of 16×9 and 16×10 (which is favoured by computers).

Considering the way EDID works, if all of this was hooked up via an HDMI DA or matrix switcher, the 1920×1080 LCD panel will never receive a native resolution signal and will not provide the best possible image.

The resolution going to all displays will be 1280×800, and the ‘Full HD’” display will internally scale down the image so that it fills the screen.

Best practice would be to have all displays presenting the same native resolution of 1920×1080 to ensure a 1:1 pixel match, however in real life this is not always achievable. Enter the external scaler.

To ensure best image quality and a stable system, it is crucial to know the native resolutions of all displays in the system. Yet it seems that not all LCD panels are what they claim to be, especially those at the lower end of the price scale.

On numerous occasions while conducting training sessions we found that some displays claiming to be ‘Full HD’ will present a 1920×1080 EDID when connected to a computer, while having a native resolution of 1680×1050 or some other specification.

(Native resolution can be verified quite easily with free software such as ‘moninfo’, or you can splash out and use a Quantum data tester).

I don’t have all the facts on this, but one logical explanation comes to mind. A vast range of displays (especially domestic ones) is on offer from 21-inch to 32-inch – and seemingly every conceivable size in the 40-60 range.

Glass manufacturers don’t make individual panels for each size in this vast range. Instead, the panels are cut from a few variants to the many sizes on offer, then the aforementioned scaling chip does the work to present the ‘Full HD’ EDID to the source. In a few cases we found LCD panels with a ‘native’ 1680×1050 resolution that requested a 1920×1080 resolution from the source.

So what is wrong with that? Probably nothing much, as you get what you pay for. However, we strongly recommend physically checking the native resolutions of any panels you intend to put into a design, especially if optimum resolution and sharpness of image are paramount.

In the case above, the LCD displayed the 1920×1080 signal from a laptop quite well, but when we forced the resolution out of the computer to 1680×1050 to achieve an exact pixel match, it changed from acceptable to perfect. (This is the catch mentioned above.)

To summarise, the main function of scaling is to change one resolution to another by adding or subtracting pixels and, where aspect ratio change is involved, to skew the pixels to match. Think about short, fat people images (4×3) being stretched over a 16×9 display in extreme cases.

So, is scaling bad? Not at all, if it is applied correctly and factored into the design of the system from the start.

Also noteworthy: A scaler is NOT a “Plug and Play” device! In order for it to function properly the outputs have to match the native resolution of the display attached to it, thereby effectively omitting the internal scaling chip in the display itself and letting the External do the work of matching up the various sources.

As far as 4K is concerned, there is practically no material available and few computer graphics cards are able to output these resolutions, yet it is the current buzz. So, for some time to come everything going to these displays will be scaled up to match – but it won’t necessarily result in an improved image.