Scaling & format conversion
Why every output may need its own resolution.
Every flat panel and projector has a native resolution: the fixed grid of pixels it is built with (Chapter 2). Sources, on the other hand, output whatever they like: an old laptop at 1024×768, a new one at 1920×1200, a media player at 4K. Somewhere between source and screen, the image has to be converted to fit. That is the job of a scaler.
What a scaler does
A scaler receives a video signal and builds a new one at a different resolution, recalculating every output pixel from the input pixels around it. Most scalers do more than resize:
| Conversion | What changes | Example |
|---|---|---|
| Resolution | Pixel count up or down | 1280×720 laptop → 1920×1080 display |
| Aspect ratio | How a picture is fitted to a different shape | 4:3 slides on a 16:9 screen |
| Frame rate | Frames per second | A 50 Hz camera feeding a 60 Hz display |
| Interlaced → progressive | Deinterlacing into whole frames | 1080i broadcast feed to a modern panel |
| Colour format | Colour space, chroma or bit depth | 4:2:0 input to a 4:4:4 output |
- Resolution
- What changesPixel count up or down
- Example1280×720 laptop → 1920×1080 display
- Aspect ratio
- What changesHow a picture is fitted to a different shape
- Example4:3 slides on a 16:9 screen
- Frame rate
- What changesFrames per second
- ExampleA 50 Hz camera feeding a 60 Hz display
- Interlaced → progressive
- What changesDeinterlacing into whole frames
- Example1080i broadcast feed to a modern panel
- Colour format
- What changesColour space, chroma or bit depth
- Example4:2:0 input to a 4:4:4 output
Scaling has limits. Upscaling makes the image fill more pixels, but it can't restore detail that was never captured; good scalers just make the result look smooth rather than blocky. Downscaling throws detail away, so fine text from a 4K source can become hard to read on a 1080p screen. Every scaler also holds part or all of a frame in memory while it works, which adds a little latency — something to keep in mind for live camera work and lip sync.
When the shapes don't match
Resolution is only half the problem. If the source and display have different aspect ratios, the scaler has to choose what to do with the difference:
- Fit (also called letterbox or pillarbox) keeps the whole picture and its shape, and fills the leftover space with black bars.
- Fill (also called zoom or crop) covers the whole screen and cuts off whatever spills over the edges.
- Stretch fills the screen by scaling width and height by different amounts, distorting shapes.
Scale until one dimension fills the screen; bars fill the rest. Nothing is lost or distorted.
Up ×1.41
Upscaling enlarges pixels; it can't add detail.
75%
Bars at the sides (pillarbox).
4:3 → 16:9
Why each output may need its own scaler
A matrix switcher might feed a 4K panel, a 1080p confidence monitor and a 1920×1200 projector at the same time. Each display has a different native resolution and aspect ratio, so a single “correct” signal doesn't exist. A scaler on each output lets every display receive exactly its native format, whatever source is routed to it.
That same arrangement is what makes seamless switching possible (last lesson): because each output scaler produces a constant signal, the display never sees the source change. And because the switcher handles the conversion, its EDID (Chapter 3) can ask sources for one consistent format, without passing through each display's preferences.
Key takeaways
- 01Displays have a fixed native resolution; a scaler converts each source to it.
- 02Scalers can also convert aspect ratio, frame rate, interlaced to progressive, and colour format.
- 03Upscaling can't add detail; downscaling discards it; all scaling adds some latency.
- 04Fit keeps everything with bars, Fill crops, Stretch distorts — use Fit for presentations.
- 05A scaler on each output gives every display its native format and makes seamless switching possible.
Check your understanding
Q1A 4:3 source is shown in Fit mode on a 16:9 screen. What does the audience see?
Q2A 1920×1080 laptop feeds a 3840×2160 panel. What does upscaling achieve?
Q3Slide footers are cut off on a TV, although the switcher outputs the TV's native resolution. Likely cause?