Color Theory, White Balance and RAW - 10/06/2006

Originally I decided to write an article on White Balance but this tutorial expanded. My vision of this project is to help people who new to digital photography and veterans who have an interest in learning more. I have found some people may have not taken interest in learning about White Balance or RAW possibly due to articles that are too technical that may lose people quickly. My goal will be to keep this as simple as possible. I am going to begin with basic color theory. Two reasons, first being that I think before someone learns about camera white balance they should have knowledge of how humans see or perceive color in the natural world. By the end of this article you will see that our eyes and cameras are not much different. Second, I have been in the printing business for quite a few years, many in technical training. Even to this day, color theory is still my favorite training seminar.

Cathy seemed interested so I asked to her to get involved and I'm glad I did. I was not going to cover color cast but it is the logical progression. I was going to develop a separate tutorial on RAW but we decided to combine the two. It became a little longer than first expected, however we feel it is worth the read. We would put our names to each section contributed.

What is color?

When I start my seminar I always ask the same question - What is Color? It's pretty rare that I get the correct answer. I think most people know what it means, it's just the wording. The answer is - Light Is Color. So we will begin this by talking about light. There are many sources of light. Let's pick our very own natural source the sun, during a mid summer day. The sun produces many light waves in the visible spectrum but the three predominant ones are Red, Blue and Green or RGB. When I say predominant I am referring to humans. These are also known as the primary colors of light. Equal amounts of Red, Blue and Green light waves produce white light. Say what? OK, let's prove this statement. The best demonstration is right on your monitor screen. Use word, paint or any software and create 3 boxes that are around 3" by 3". Color one Red, one Bright Green and one Blue. Hopefully some of you have a powerful magnifier. It should be powerful enough so you can see the individual color dots or rectangles on the screen. I use a 50X magnifier. If you don't have one draw the boxes anyway, I have made an illustration. For those with magnifiers hold it up against the Red square, the Green square, the Blue square then finally pick a White area on your monitor. Almost every person in my seminar does a double take at this point. Observing the red area they see only the red dots illuminated, in the green square only green dots are illuminated and in the blue square are only blue dots are illuminated. But when looking at a white area all Red, Blue and Green dots are illuminated yet when they pull away the area looks white. At this point they are convinced, but why does this happen? Now we have to talk about your eyes. Your eyes have Rods and Cones. The rods are only sensitive to the presence of light. You walk into a dark room the Rods make your pupil dilate. Walk outdoors your pupils close. The cones are sensitive only to color. The cones are also known as color receptors. Some cones are sensitive to Red Light waves, some are sensitive to Green Light waves and some are sensitive to Blue Light waves. When all our cones are stimulated by equal amounts of RGB light waves we see white.

If you don't have a magnifier this is what your monitor would look like. Keep in mind your monitor could be rectangles more tightly spaced. All monitors are not the same.

Red Square	Green Square	Blue Square
Any white area on your monitor

I'm hoping at least one reader is saying wow by now. If you take a piece of white paper outside during the summer mid day sun and look at it, equal amounts RGB light waves are hitting the paper and bouncing back and stimulating all your cones so the paper looks white. What if you look at black piece of paper? Black absorbs all light waves. No light = no color. Is black a color? What if you look at a red piece of paper or a red apple? The red pigment in the paper absorbs Green and Blue light waves, reflects back only red light waves. Only our red cones are stimulated so we see red. What about a ripe banana? Yellow absorbs Blue light waves and reflects Red and Green light waves. When our Red and Green cones are stimulated we see yellow. Now I can really go on here but I won't because this can get really complicated. You now know enough to understand basics of color theory. Just one more point. The apple or the banana, do not really absorb all the light waves that I mentioned. Some of the light waves do sneak out in varying percentages. It all depends on the pigment of the object your viewing. These small subtle variations are the reason humans can see billions of colors.

Now I will ask you two questions. First question: Where is color? Is color in our natural world or is it in our heads? Color is in our heads. There are only light waves out there, bouncing around, being absorbed and reflected back to us and our brains process it as color. What a way to look at our world. Second question: This one I made up as I was writing this. Remember the question "if a tree falls in the forest and no one is there does it make a sound"? If no one is in the forest is there color? A person who is color blind does not mean they cannot see color. One or more color receptors are not functioning properly. I have read that children live in a more vivid and colorful world because their receptors are young. Not like my arthritic ones. Everyone has heard that dogs are color blind. This does not mean they see in black and white. They only have two sets of cones and they are much smaller. They are missing cones that cause red/green color blindness which is common in human color blindness. If dogs were the intelligent beings on this planet they would have developed their own cameras and color models.

White Balance

Now about white balance. Your camera white balance works pretty much the same. Camera technology varies as Sony uses 4 colors but the outcome is the same. Just so we are on the same page I will continue to refer to it as RGB. Your camera is actually looking for a white area in the image you are about to shoot so it has a reference. If you take a landscape image during a sunny mid day the one with some clouds usually looks better than one with just blue sky. When you use Average or Auto white balance it is trying to do its best to balance the light (equal amounts of RGB) with the actual lighting conditions you are giving it to work with so you can preserve the white objects and control color cast in your image. We will talk about color cast later. It has to adjust from overcast, to sunshine, to fluorescent, to tungsten and so on. Most of the time, it does a fairly good job. If you shoot under tungsten light you can set your white balance to tungsten. The computer will know that there is not an equal amount of RGB light waves, the light is warmer and adjust to preserve the white objects in your image. Same goes for fluorescent. Remember though not all tungsten and fluorescent lights are alike so even setting it to the correct white balance your camera is still making its best guess. Remember film days? You could buy daylight, shade, fluorescent or tungsten. Now the digital camera does this. So actually what are trying to do is preserve the white in your image and the all the colors will fall into place. If there are no white areas in your image it will use neutral areas like grey.

Say you are taking a picture of an antique white cabinet under tungsten light and your want to be sure the cabinet is white. So what is the best way to control your white balance? Custom White Balance. When you use Custom White Balance you are telling this to your camera. "Camera, I don't care if this is tungsten light or any variation of it. In fact I don't care what the light source is, as far as you are concerned it is emitting equal amounts of RGB light waves". Learn how to set your camera to Custom White Balance. There is another way to control white balance: the flash. The Auto flash setting emits more balanced amounts of RGB light waves however it is usually less desirable.

Here is a simple test. Grab two sheets of white paper. Place one under a tungsten lamp. Put a few blue and red colored items around it. Set your camera to Average or Auto white balance. Compose so the white sheet is about 50% in the image area and take the shot. Follow the Custom White Balance instructions in your cameras manual. Take your lens off auto focus, place the other white sheet over the end of your lens, aim directly at the light bulb and take the shot. Make sure you complete any steps to finish the set up. Put the lens back in auto focus, compose the same way you did on the sheet of paper under the lamp and take another shot. Load the pictures and observe on your monitor. The paper in the Auto White Balance image should appear yellowish while the paper in the Custom White Balance image should appear pure white. The reason for the yellowish appearance is the white balance is out of balance. Now you have been introduced to color cast. It is an undesirable color tint on an image, in this case being yellow. The Custom White Balance setting should appear pure white. If there is no difference try it again. If this continues your cameras Auto white balance is awesome. Try another light source. Finally look at the objects around the paper with custom white balance. They will appear cooler than the ones in the average white balance, no yellow tint. Now when you read a review about a camera and it states the Auto White Balance is not very good you know why. It may lean towards a warm or a cool color cast. No two camera manufacturers are alike. No two models from one manufacturer are alike. Manufacturers are always improving/changing their products.

Here are some samples of the test. As you can see there was a significant improvement setting the camera to tungsten however the purest white came out with Custom White Balance. You can see the difference in the color of the desk.

Auto or Average White Balance	White Balance Set to Tungsten
Custom White Balance

What are you doing to your camera when your shooting a still in the kitchen under a fluorescent light, the tungsten light is on because someone else is in there and there is natural light coming in through the window? You are giving it a headache! Use Custom White Balance!

Just because you shoot outdoors does not mean you will avoid color cast. Again it depends on the accuracy of your camera's Auto White Balance and the light conditions throughout the day. Below is a Kelvin scale. Kelvin is the temperature of light. It's backwards to the way we have learned about warmth. As the scale goes down the light becomes warmer. The table shows that the temperate of daylight ranges from 5000 to 10,000. Sunrise and sunset 2000- 3000. Check your cameras default Kelvin setting. It will be about 5,200 which about equals the mid day sun.

Here is a comparison of an image shot using Auto White Balance and Custom White Balance.

Incorrect white balance - blue color cast

Correct White Balance

During the Custom white balance test we used paper as a filter. Your can use coffee filters and I have heard of people using Pringle chip lids. Your camera manual may state to take a picture of the light source. Do not take a shot of the sun through a coffee filter! It could fry the sensor. Daryle Holstrom has a great tutorial on using coffee filters that can be found in the tutorials section. I purchased an Expodisc which allows me to shoot directly into the sun. A little expensive but I like it.

Your camera may come with balance correction feature. This feature is tough to use unless you have experience with it. It's kind of a guessing game, trial and error because you don't really know the exact temperature of the light conditions and there is no way to measure them. This feature replaces the color temperature correction lens filters from the film days. If you shoot in RAW this feature does nothing anyway.

Common Problems for Photographers

Exposure and white balance are the two most common problems photographers have. Learn how to lessen these problems and you'll be a lot happier with your photographic results. If exposure and white balance are off, they will ruin good pictures. You will end up with pictures that are too dark or light (under or overexposure), pictures with overall color casts of yellow, green, orange, brown, magenta, or blue (white balance errors) or pictures with a combination of both problems. If you overexpose and lose detail in the Whites, the detail will be gone. Remember, if the information is not there, your software can not correct this. If in doubt, always underexpose if you want to retain detail in the Whites, or bracket your shots-unless of course the effect you are going for is a High-Key image.

Try to learn to correct the problem when taking the photograph instead of fixing the problem after the fact. It's much easier, and while in your digital software program you can get creative with results or maintain a "purist" image. It will give you more avenues to work with. Shooting images in the RAW format will assist you in the corrections if they are required in post processing.

To control exposure problems, learn to meter your scene correctly. When you set your camera to spot metering and meter off a given area, the camera is going to try and expose the scene so that that given area turns out neutral (18% grey) grey. If you point your spot meter at a dark object, your camera will try to overexpose the subject. If you point the camera at a bright object the camera will try to underexpose the subject. Try to meter off something Neutral. Examples are darker vegetation, lush green grass or a deep blue sky.

What is RAW?

When I first started to learn about RAW I had a tough time. It's very simple however no matter how much I searched I could find no simple explanation. RAW is like taking 50 pictures of the same image in JPEG. Why would you want to do that? This is the most important picture in your life and you want to get it right. First you set your camera to Auto White Balance and then you start taking pictures starting at the lowest exposure and you work your way up through all the exposure stops (1/3 or ½ depending on your camera) until you reach the highest exposure. That's about 12 shots. Now you have to repeat that with all the different White Balance settings, saturation, etc. Load up all these pictures and sort through them until you find the perfect image. Or you can take just one shot in JPEG and change your brightness and contrast settings. When you shoot in JPEG your camera takes the information and immediately converts it into the final image. Also JPEG is a lossy format which means that you degrade your image every time you make a change as you are working on it with your image editing software. Lossy = loosing information. Also you cannot change the white balance. One shot in RAW captures all the exposure, white balance, etc settings but does not process it to a final image. It just stores all the information. Now you know why the files are so big. When you load up your RAW image you can make all the changes you want to exposure, white balance before converting to your final image for the final touch ups, etc. I have accidentally left my white balance in tungsten and shot during in daylight. No problem. RAW captures everything. One more thing. You should convert to a lossless format like TIFF. Lossless = no loss of information. When working in your image editing software the TIFF format does not degrade your image. Then when complete convert to JPEG for web or print. You should consider setting up a file structure. Treat your RAW files as negatives, Tiff as working files and JPEGS as finals. It is much easier to track. If you are concerned about storage external hard drives are inexpensive these days. Store your RAW and TIFF files there.

The Advantages of RAW

I will show the simple advantages of shooting in RAW. I will demonstrate visually, as I am a visual learner. Take our recent outings of The Café's get together at the Washington DC zoo.

The day was cloudy overcast, with drizzling throughout the day. Very low lighting in areas of the zoo, throughout the park.

This is an example shot taken with my Canon 10D, notice white balance set to Auto. Oops.

Notice the Blue castings in the shadows/highlights. Notice the histogram as well, it weighs heavier on the dark side. What to do, what to do?

Below is the same image with the settings changed within Photoshop CS2 RAW conversion. I set White Balance to Cloudy (take notice of the new histogram):

Below, another image from the Zoo, but now with my cameras White Balance set within the camera to Cloudy:

Notice the overall image has no color castings. This image has no adjustments made to it, notice though that some shadow areas could be pulled out of the darkness. This can also be done with the RAW converter without loosing any information yet. The beauty of RAW.

My point being, take control of your settings from the beginning. In the event you forget to set your camera or you set it incorrectly, shooting in RAW gives much more leverage to a final product with correct color without a lot of knowledge needed to color correct within Curves.

Conclusion

Well I guess we're done. I hope we cleared up some of the mystery about white balance and RAW. Cathy who helped me with this tutorial mentioned that both she and Todd both see many images that would be even better if color casts were removed. Now you understand how they got there in the first place. Look at your photos. Do they have color casts? If they do you can also correct them in image editing software. I always shoot in RAW and never worry about exposure or white balance. Also you don't have to follow the rules at all. When I view a RAW image before processing I check every white balance because just like Forest Gump said "you never know what your gonna get". I had to sneak in one line from a movie. I seen a photo of Dandelions going to seed which obviously should have been white but was set to either incandescent or fluorescent that gave them a beautiful blue tint. You may want to retain that golden glow during sunsets. At least now you will have full control when you want it. Have fun.