Putting it all Together—Exposure and White Balance
A gray card.
If your camera displays a histogram, the one for the gray card should be a spike right in the middle of the horizontal axis.
The Macbeth color chart.
The Kodak Color Separation Guide (top) and Gray Scale (bottom). These two printed cards come together in large 14" (Q-14) and small 8" (Q-13) sizes.
When shooting with a digital camera, your biggest advantage is that you can see the image you just captured and make adjustments as you go along. Only when it looks perfect on the monitor, need you go to the computer to see what it looks like enlarged. However, when shooting a number of objects, as you might for a catalog, or an on-line business, it helps to develop a system that makes things faster and easier. When shooting in a studio, a video out connection on the camera allows you to connect it to a TV so each image that you take is instantly displayed. Not only is the screen much larger than the camera's monitor, it is adjustable. (Some camera monitor's are also. Most let you adjust brightness, and a few let you adjust hue and saturation). Another advantage of the CRT on a TV is that the density of the image doesn't change depending on your viewing angle. On many camera LCD monitors it does. You can also use the same setup to take portraits and let the subject see themselves immediately as each picture is taken. It makes a session a lot more interactive.
There are also things you can do to be sure you are using the best possible exposures and white balance. Although you can see the results of your shots on the monitor, and make adjustments as you go along, there are ways to be more efficient and more accurate. They involve shooting standardized cards containing gray scales and color samples.
- Shooting a gray card helps you place middle gray precisely where it belongs—right in the middle of the histogram's horizontal axis. When you shoot the gray card under the same light you'll use to photograph the subject, the histogram should show a spike right in the middle of the horizontal axis. If it's to the left, the image is too dark so you should use plus (+) exposure compensation to increase exposure and move it to the right. If it's to the right, the image is too light. Use minus (-) exposure compensation to decrease exposure and move it to the left.
If all of your light sources do not have the same color temperature, you can white balance for one mix but not for all possible combinations.
Here Quinlan sits in front of three lights-red,green, and blue. Where he blocks the light from one bulb, a shadow forms from a mixture of the other two bulbs. You will get a similar effect in
areas lit from sources other than the mix of light for which you have set white balance.
Once you have placed middle gray, you can then check the dynamic range and white balance and adjust the camera or attached TV to be sure you're seeing the best possible colors. To do this, you can use the same exposure setting to photograph Kodak Color Separation Guides and Gray Scales available from Calumet or B&H Photo. You begin by photographing these cards under the same light you use to photograph your subjects. You can also place them along the edges of any art you are photographing for more accurate reproduction or photo editing of your artwork.
- The KODAK Gray Scale lets you see if you are capturing all of the possible tone values and making full use of the camera's dynamic range. The scale has 20 steps in 0.10 density increments between 0.0 white and a practical printing black of 1.90 density. When you photograph this scale you should be able to adjust the monitor's or TV's brightness and contrast controls so you can see each and every one of the 20 steps. If the whites all run together, you are overexposing. If the blacks do, you are underexposing.
- The KODAK Color Separation Guide helps you compare the color of the subject with known printing colors. You can use it as a guide when adjusting your camera's white balance, hue, and saturation, and if you send the photo to a printer for inclusion in a catalog it helps them create separation negatives need to print the images. The card contains nine patches, with two saturations of each patch. When you shoot color patches, your goal is to make the monitor display them as close to the original colors as possible.
The camera's video out terminal can be used to connect a TV set while you are shooting. This allows you to immediately review images greatly enlarged. (The foil on the top light in this image is used to block light from the background).