Color Temperature
Wednesday, August 4, 2010
Color temperature is measured in 'kelvins' formerly known as 'degrees kelvin'. To get the idea, think of a piece of metal being heated in a fire. First it gives off a reddish glow and, as it gets hotter, the color gets whiter and then, as it really warms up, it starts to give off a bluish glow. In Physics of course, we can't use any old bit of metal for the kelvin scale, we need a 'theoretical black object'. The photographer's color temperature chart is a loose interpretation of the kelvin scale, the numbers are not used in any precise manner.
As photographers all we need to know is that different types of light source emit different colors. 5000 kelvins is what we photographers call white light and is represented by 'average daylight', whatever that is, actually it's fairly obvious if you look at the chart below. We also need to know that household bulbs give off an orange light and a cloudy day will appear blue. Here's a color temperature chart covering typical light sources. In the last column I have put my recommended camera setting for each type of light. As you can see, one setting can cover several steps on the scale.
When we look at objects with our eyes, we perceive white objects as white, and gray objects as gray, no matter what sort of light source we are viewing them by. This is because our brain is making the conversion for us. We 'know' that wall is white so we don't notice that it looks yellow at night (with the room lights on). If you really start to look you can see these color differences to some extent, but they are not as noticeable as they are to the camera.
Modern cameras have 'automatic white balance' so why can't we just leave it all to that? The AWB does do quite a good job but it isn't 100% accurate all the time. So sometimes we need to be able to do a few corrections ourselves
[get this widget]
As photographers all we need to know is that different types of light source emit different colors. 5000 kelvins is what we photographers call white light and is represented by 'average daylight', whatever that is, actually it's fairly obvious if you look at the chart below. We also need to know that household bulbs give off an orange light and a cloudy day will appear blue. Here's a color temperature chart covering typical light sources. In the last column I have put my recommended camera setting for each type of light. As you can see, one setting can cover several steps on the scale.
When we look at objects with our eyes, we perceive white objects as white, and gray objects as gray, no matter what sort of light source we are viewing them by. This is because our brain is making the conversion for us. We 'know' that wall is white so we don't notice that it looks yellow at night (with the room lights on). If you really start to look you can see these color differences to some extent, but they are not as noticeable as they are to the camera.
Modern cameras have 'automatic white balance' so why can't we just leave it all to that? The AWB does do quite a good job but it isn't 100% accurate all the time. So sometimes we need to be able to do a few corrections ourselves
[get this widget]
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