white balence and noise in photos

[PhotoGirl]

Hi All,
I was doing some photography reading, and I keep seeing the terms "noise" in photos and "White Balance"; can anyone please tell me what these terms mean? And some tips on how to aviod having them in your photos? thanks.

[another view]

White Balance (WB) relates to the color temperature of the lighting that you're shooting in. There won't be a test on this, but it's good to know a little about it - daylight (mid-summer sun) is about 5500k, incandescent lightbulbs about 2700k, overcast days maybe 8-10,000k. It's measured in units of degrees "k" or Kelvin, so that's what the numbers mean. Most cameras have an auto WB and it's usually not too bad. The problems with a bad white balance is if the camera is set wrong (by your doing or auto WB being fooled) then your pictures may be really blueish or orangish. If you have any pre-sets on your camera (daylight, cloudy, indoors, etc), then experiment with this, you won't hurt anything.

Noise is basically the digital equivalent of film grain. Here's a shot from my compact digital at ISO800 with no noise reduction, as an example. Actually this one doesn't show it too bad, but compared with a really clean file it isn't so good. One thing interesting (to me at least) is that kind of like film, high ISO's are a little contrastier than lower ISO's.

[Franglais]

Hi All,
I was doing some photography reading, and I keep seeing the terms "noise" in photos and "White Balance"; can anyone please tell me what these terms mean? And some tips on how to aviod having them in your photos? thanks.

White Balance:

The human eye sees white objects as being - white. It ignores differences caused by the "white" light falling on the object being slightly coloured - sunlight is bluish, a light bulb is reddish, a flourescent tube is greenish, etc.

Digital cameras faithfully record things the way they are, with the colour cast from the light falling on the subject. "White Balance" is just a way of telling the camera to apply a correction for the type of lighting so that a white object comes out white.

Noise:

You remember audio tapes/cassettes? When you had a cassette that was recorded too low, you turn up the volume and sure it's louder but there's also the background hiss. That's "Noise" in audio terms. You've amplified the signal but also the errors coming off the tape.

In digital cameras it's the same problem. The sensor has a basic sensitivity to light of 100 ISO (for example). If you set the camera to 1600 ISO then the camera will take the very faint signal from the sensor and amplify it so it has the same strength as at 100 ISO. But it will also amplify the errors, which appear as coloured specks. "Noise".

Charles

[JSPhoto]

Hi PhotoGirl,

If you are getting a blue tint to your photos they are too cool on the color temp, if you get a yellow tint they are too warm, you want to get the median where the white colors look natural without a tint. Many cameras allow you to auto bracket the WB to help get an idea where you need to be and what looks more natural color wise.

JS

[PhotoGirl]

thanks guys for your answers.

so, how do you know if you have auto white balence on your camera? and any other tips to keep in mind to avoid having an off-colour photo due to white balence? thanks.

[Franglais]

thanks guys for your answers.

so, how do you know if you have auto white balence on your camera? and any other tips to keep in mind to avoid having an off-colour photo due to white balence? thanks.

You know there's this little (or not-so-little) book that comes with the camera? This is the instruction manual. Among other things it tells you where in the profusion of menus and buttons that you have on the camera are the white balance controls.

Alternatively - photograph a white sheet of paper in sunlight. Then photograph the same sheet of paper indoors by just tungsten room lighting. If it comes out the same grey colour then your camera has auto white balance working.

Modern digital cameras are pretty good at auto white balance. The only tip I can think of is - avoid having two different-coloured light sources in your picture - example: flash and tungsten light. On my D70 if I forget to switch manually to flash light balance (similar to sunlight) and I use my flash to brighten up pictures done indoors on tungsten light then the camera will set auto white balance to tungsten and the light added by the flash comes out horribly blue. Better to leave the flash as white and let the room light go reddish..

Charles

[another view]

Alternatively - photograph a white sheet of paper in sunlight. Then photograph the same sheet of paper indoors by just tungsten room lighting. If it comes out the same grey colour then your camera has auto white balance working.

Note that there's a good chance this paper will appear grey and not white. I won't get into the "why" of that, just realize that grey is OK unless it has a bluish or yellowish tint to it. That's what you're checking for.

And check the manual - it will show you the options that you have for your camera. In my experience, the farther you get away from sunny outdoor light, the harder auto WB will have. This means that incandescent light will appear a little yellowish (which isn't always bad IMO), and cloudy overcast days may appear a little bluish.

[PhotoGirl]

thank you!