Luminance and brightness

What the hell's the difference between luminance and brightness?

We'd guess you'd just like the one term that is effectively a measure of the brightness of a colour. Brightness, within Imagina is just that, a very accurate measure of the brightness of a colour. Our measure of brightness of colour is just one reason why our brightness handling is so much better than other software out there.

Luminance, can be viewed in the same way but is much less accurate. It has been included within Imagina for historical reasons, and it follows the ITU-R BT.601 standard to the letter. Luminance though, isn't a good measure and can differ from the actual brightness by more than 10 times. It should therefore be avoided wherever possible. As far as we can tell, you'd be very hard pressed to find an image editing package out there that handles brightness any more accurately than this standard dictates. Let's have a look now at just how inaccurate luminance can be.

A typical colour chart before it is converted to grey-scale.

Now the same chart in grey-scale using luminance as a determinant.	And the chart again but this time using brightness as a determinant.

Look at the difference in the greys between these charts, they can be simply enormous. The most obvious problem here is with blue, which although (rightly) has been given less prominence than either green or red in it's grey equivalent, the luminance algorithm has really undervalued it's brightness contribution.