Interpreting the results
To start with you'll be most concerned with two graphs: RGB levels and Colour temperature. Before we start looking at them please note that inexpensive entry-level probes like the Spyder 2 are not too accurate at low light levels so for the purposes of calibration, when viewing graphs you'll want to dismiss readings between 0 and 20 IRE. Don't worry it'll all make sense when you see the graphs!
RGB Levels
In a perfect TV display red, green and blue levels should be identical such that they will appear as three lines stacked on top of each other. In the real world there will be some discrepancy between the output levels of the three primary colours, the degree to which these vary is called 'delta E', you want the difference in colour levels to be as little as possible across each grey level (IRE).
Have a look at the following graph:
Above you can see the
pre-calibration performance of the Toshiba 42X3030D reviewed by hdtvtest.co.uk; in order words, when they received their display this is how it performed right out of the box. Note that the levels start to separate at several points in the graph but generally they track one another.
Note: The separation that occurs between 0 and 10IRE is most likely due to the inaccuracy of the colorimeter device when used at very low light levels.
Now take a look at the same graph showing how my TV performed out of the box. It is the very same model (42X3030D) so you might expect it to perform similarly but you'd be wrong; notice what a huge difference there is - the blue level is way off, it is 30%+ over-saturated.
The other difference is the magenta line is missing from my graph. The magenta line plots the 'delta E', which as we discussed is the degree to which the RGB levels differ in their saturation. The blue level on my display is so horribly out of whack that the 'delta E' is off the charts!
Generally we want to minimize 'delta E' so that it is around or below 4. If I remember correctly at this level the human-eye cannot perceive any difference between the RGB levels.
Colour Temperature
When we talk about colour temperature, for example 6500K, we are talking about a theoretical black entity which when heated to the specified temperature (measured in Kelvins) emits light. Think of a black iron bar that you're heating with a blow torch, as it grows hotter it glows red, then yellow, then white hot, etc. The lower the temperature, the "warmer" or more yellow the light. The higher the temperature, the "cooler" (ironically) or more blue the light.
You may have heard of the term D65. This is a name/label for the particular mixture of colours which make up white at a particular temperature. It corresponds roughly to a midday sun in Western / Northern Europe. Movie footage tends to be shot around this time as it provides the optimum conditions for natural illumination.
Its important to make the distinction that while D65 has a colour temperature of 6500K they are not one and the same. When we calibrate against D65 we are trying to achieve the colour white with a 'temperature' of 6500K. If we simply tried to achieve 6500K we could obtain all manner of colours whose RGB levels approximate to 6500K.
Here is a graph showing the
pre-calibration performance of the hdtvtest.co.uk review model:
And as before here is the same graph showing the performance of my TV display. Can you spot the difference?
Even at the warmest colour setting available in the user menu the colour temperature of my display is well in excess of 6500K; as a result there's just no way my set can output D65 white; black levels and contrast ratio are nowhere near as good as they can be.
Clearly the blue over-saturation plaguing my set has caused the light to be cooler / bluer and raised the overall colour temperature.
In summary, if there's one thing you should take from this it's that there can be a large difference in the performance characteristics between two displays, even if they are from the same manufacturer and have identical model numbers! Consequently, when someone posts their preferred settings in the forum, bear in mind, they may not have the same effect on your TV display.
So how did I solve the blue over-saturation issue? In my next post I'll discuss how to make user and service menu adjustments and monitor their effects.