all I learned about White Balance (long)
Posted: Mon Jan 17, 2005 10:44 amI was following a thread at dpreview this week about white balance and a possible problem with the D70 and I realised that I don’t really understand WB. So I went on a mission to understand and this is what I have learned in as simple a terms as I can put it.
All light has a particular colour temperature. This is measured in Kelvin (K). Basically K is like celcius but on a slightly different scale.
If you wanted to generate light of a particular temperature, say 5200K, you would get a lump of black metal and heat it up to 5200K. It would glow white hot and would generate light with a colour temperature of 5200K.
5200K just so happens to be the temperature that Nikon says it is in broad daylight. When you set your camera to the little sun the camera thinks you are taking pictures in broad daylight. This is actually a little controversial because many people seem to think that 5400K is actually broad daylight. I would say that in the harsh Australian light this is probably right. To dial in 5400k just go to the daylight WB setting (ie the little sun) then dial in -2 (this will take out the blue tinge in your photos).
So what happens if the colour temperature that the D70 is set to is not the same as the actual colour temperature.
When the D70 takes a picture it doesn’t really ‘see’ the colours. It just sees a bunch of data about the relationship between the different colours with no reference point. The reference point is the colour temperature. When we or the camera anchors that reference point then everything else falls into place.
Here is a way of thinking about Kelvin that explains how your photos will be processed by the D70.
Think of Kelvin as units of ‘red/yellow’ light. At 5200K there are 5200 red/yellow units of light in a given scene. If the camera chooses 5200K then there is the perfect amount of red/yellow for the scene. But what if the scene is actually in your living room with only an incandescent globe spitting out 3700K. Well, if the camera is set to 5200K it will add the wrong amount of red/yellow to the scene. Here is the D70s thought process:
• Ah I see he’s taken another picture
• WB is set to daylight, 5200k
• Therefore I need to add 5200 units of ‘red/yellow’ light to balance all that bright white/blue light
What happened in the real world:
• Picture taken indoors with a 3700k incandescent globe as the light source
• WB incorrectly set as daylight, 5200K
• Camera incorrectly adds too much ‘red/yellow’ light to the picture.
So your picture will look like this:
Rather than this:
What if I had my camera set to incandescent and took a picture in daylight? The camera adds enough ‘red/yellow’ to a normal incandescent scene, ie 3700 units worth. But the real scene needs 5,200 units. So what happens? There is not enough red/yellow and the picture appears to have too much cool white/blue light.
So here are a couple of rules to explain this:
• If the D70’s WB is set to a setting with a colour temperature greater than what exists in the real scene then the picture will end up with too much red/yellow in it.
• If the D70’s WB is set to a setting with a colour temperature less than what exists in the real scene then the picture will end up with too much blue/white in it.
The golden Rule:
Increasing the Kelvin increases Yellow in your picture
How do I know what colour temperature the different settings in the D70 are?
Your manual has them all. Basically as if you press the WB button on the back of the camera and spin the rear wheel the icons progress across the LCD screen to the right. Other than Auto the settings (should) reflect increases in colour temperature (K) as they move across in the following order:
Incandescent Fluro Daylight Flash Cloudy Shade
But what is the problem with the D70’s WB?
There is a very long thread in DPreview on this which is actually what prompted me to learn about WB and write this thread.
Here it is:
http://forums.dpreview.com/forums/read.asp?forum=1034&message=11733370
Basically there appears to be a problem with the colour temperatures that have been set to go with the particular in camera WB settings.
I did my own test and here it is:
I believe that what has happened is that the Flash and Cloudy settings have been accidentally swapped in the programming.
If all things were correct then in my test shot there would be an even progression from a blueish shot (ignore the first two which are on Auto) through to a shot with more red/yellow in it.
You can clearly see that the Flash and Cloudy settings seem to be the wrong way around.
My test was not that scientific but surprisingly effective. Various shots of an off white wall with different WB settings and the same light source (on board flash).
What this means for us?
If you use the flash setting for WB then the camera will use a colour temp of 6000K rather than 5400K. As we learned above this means that there will be too much red/yellow in our picture.
Work around: use the cloudy setting rather than the flash setting if you are manually setting WB.
One saving grace is that Auto WB doesn’t seem to suffer from this problem but I would say that a setting of WB – 2 gives me a more acceptable tone than normal WB. WB – 2 actually adds about 200K to a picture, warming it up slightly (ie adding a bit of red/yellow).
A note about RAW
I have not fully tested this yet but from reading another post today about someone playing around with Nikon Capture it seems that NC has the WB setting correct. So if you take a picture and have the in camera WB set to Flash and then when you get to Nikon Capture you set it manually to Flash the two pictures will look slightly different.
Will the problem be fixed?
No one is absolutely sure this is a problem yet. If you look at the forum on dpreview then there is still some dispute as to whether there is actually an issue.
My conculsion is that there is a problem. There is a simple work around. If you want to manually set the the WB to Flash set it to Cloudy instead. (Something else you might want to try. Use Cloudy rather than daylight as 5,400K is probably more accurate for the Aussie sunshine.)
Hopefully there will be a firmware fix. The issue has been reported to the tech guys at Nikon and they have been able to replicate the problem.
Maybe, Birdy can raise the issue through Maxwell (that is if he agrees with me
)[/i]
All light has a particular colour temperature. This is measured in Kelvin (K). Basically K is like celcius but on a slightly different scale.
If you wanted to generate light of a particular temperature, say 5200K, you would get a lump of black metal and heat it up to 5200K. It would glow white hot and would generate light with a colour temperature of 5200K.
5200K just so happens to be the temperature that Nikon says it is in broad daylight. When you set your camera to the little sun the camera thinks you are taking pictures in broad daylight. This is actually a little controversial because many people seem to think that 5400K is actually broad daylight. I would say that in the harsh Australian light this is probably right. To dial in 5400k just go to the daylight WB setting (ie the little sun) then dial in -2 (this will take out the blue tinge in your photos).
So what happens if the colour temperature that the D70 is set to is not the same as the actual colour temperature.
When the D70 takes a picture it doesn’t really ‘see’ the colours. It just sees a bunch of data about the relationship between the different colours with no reference point. The reference point is the colour temperature. When we or the camera anchors that reference point then everything else falls into place.
Here is a way of thinking about Kelvin that explains how your photos will be processed by the D70.
Think of Kelvin as units of ‘red/yellow’ light. At 5200K there are 5200 red/yellow units of light in a given scene. If the camera chooses 5200K then there is the perfect amount of red/yellow for the scene. But what if the scene is actually in your living room with only an incandescent globe spitting out 3700K. Well, if the camera is set to 5200K it will add the wrong amount of red/yellow to the scene. Here is the D70s thought process:
• Ah I see he’s taken another picture
• WB is set to daylight, 5200k
• Therefore I need to add 5200 units of ‘red/yellow’ light to balance all that bright white/blue light
What happened in the real world:
• Picture taken indoors with a 3700k incandescent globe as the light source
• WB incorrectly set as daylight, 5200K
• Camera incorrectly adds too much ‘red/yellow’ light to the picture.
So your picture will look like this:
Rather than this:
What if I had my camera set to incandescent and took a picture in daylight? The camera adds enough ‘red/yellow’ to a normal incandescent scene, ie 3700 units worth. But the real scene needs 5,200 units. So what happens? There is not enough red/yellow and the picture appears to have too much cool white/blue light.
So here are a couple of rules to explain this:
• If the D70’s WB is set to a setting with a colour temperature greater than what exists in the real scene then the picture will end up with too much red/yellow in it.
• If the D70’s WB is set to a setting with a colour temperature less than what exists in the real scene then the picture will end up with too much blue/white in it.
The golden Rule:
Increasing the Kelvin increases Yellow in your picture
How do I know what colour temperature the different settings in the D70 are?
Your manual has them all. Basically as if you press the WB button on the back of the camera and spin the rear wheel the icons progress across the LCD screen to the right. Other than Auto the settings (should) reflect increases in colour temperature (K) as they move across in the following order:
Incandescent Fluro Daylight Flash Cloudy Shade
But what is the problem with the D70’s WB?
There is a very long thread in DPreview on this which is actually what prompted me to learn about WB and write this thread.
Here it is:
http://forums.dpreview.com/forums/read.asp?forum=1034&message=11733370
Basically there appears to be a problem with the colour temperatures that have been set to go with the particular in camera WB settings.
I did my own test and here it is:
I believe that what has happened is that the Flash and Cloudy settings have been accidentally swapped in the programming.
If all things were correct then in my test shot there would be an even progression from a blueish shot (ignore the first two which are on Auto) through to a shot with more red/yellow in it.
You can clearly see that the Flash and Cloudy settings seem to be the wrong way around.
My test was not that scientific but surprisingly effective. Various shots of an off white wall with different WB settings and the same light source (on board flash).
What this means for us?
If you use the flash setting for WB then the camera will use a colour temp of 6000K rather than 5400K. As we learned above this means that there will be too much red/yellow in our picture.
Work around: use the cloudy setting rather than the flash setting if you are manually setting WB.
One saving grace is that Auto WB doesn’t seem to suffer from this problem but I would say that a setting of WB – 2 gives me a more acceptable tone than normal WB. WB – 2 actually adds about 200K to a picture, warming it up slightly (ie adding a bit of red/yellow).
A note about RAW
I have not fully tested this yet but from reading another post today about someone playing around with Nikon Capture it seems that NC has the WB setting correct. So if you take a picture and have the in camera WB set to Flash and then when you get to Nikon Capture you set it manually to Flash the two pictures will look slightly different.
Will the problem be fixed?
No one is absolutely sure this is a problem yet. If you look at the forum on dpreview then there is still some dispute as to whether there is actually an issue.
My conculsion is that there is a problem. There is a simple work around. If you want to manually set the the WB to Flash set it to Cloudy instead. (Something else you might want to try. Use Cloudy rather than daylight as 5,400K is probably more accurate for the Aussie sunshine.)
Hopefully there will be a firmware fix. The issue has been reported to the tech guys at Nikon and they have been able to replicate the problem.
Maybe, Birdy can raise the issue through Maxwell (that is if he agrees with me
)[/i]
) able to confirm these findings on the D70?
