4K or Full HD: when the higher resolution is really worth it

What 4K behind the same lens really gives you

Full HD has 1920 pixels across, 4K has 3840. That is exactly double. If both cameras have the same lens and look at the same spot, they spread their pixels across the same width, and the pixel density simply doubles.

Calculated with a 60° angle of view and 3 metres of mounting height. Draw the line at 125 px/m for “Recognise” and you see the decisive thing: Full HD manages it to just over ten metres. 4K manages it to over twenty.

4K does not double the range in metres, it doubles the pixel density. Converted back into distance it still comes to roughly double.

When the extra cost pays for itself

There are two cases in which the higher resolution earns its money.

• You need a wide angle and detail at the same time. A yard that has to fit in the frame, and a gate within it where you need faces. With 4K you get both from one camera; with Full HD you would need two.
• You want to be able to zoom in later. Enlarging a section of a recording afterwards only works if there are pixels there. This is the case where 4K rescues after the fact what would otherwise be lost.

And there is the case where the extra buys nothing: if the camera is getting a narrow lens anyway and only has to see one small area, Full HD already reaches the density required. The additional pixels then land on an area where nobody needs them.

The cheaper route to the same effect

Before you go to 4K, check the angle of view. Moving from 90° to 60° costs nothing on most models, because both lenses are offered in the same housing. The gain in pixel density is about as large as the step from Full HD to 4K.

The price for it is area. You see less, and you see it better. Whether that fits depends on the place: at a door it is almost always right, on a large yard it rarely is.

Check the angle of view first, buy the resolution second. That order often saves more money than haggling over the unit price.

What else counts in the sum

More pixels want storing. At the same frame rate and compression a 4K camera produces considerably more data than a Full HD one. Over a retention period of several weeks and across eight cameras that adds up, and the recorder has to cope with it.

Then there is the light. A 4K sensor of the same size has smaller pixels, and smaller pixels collect less light. In daylight you notice nothing of this. In a dark warehouse a good Full HD camera can deliver the more usable picture than a mediocre 4K one.

In the end only one thing helps: work through the place where it matters. Enter distance, mounting height and task into the cctvfinder and compare both resolutions side by side. Then the decision rests on a number instead of a feeling.