If you've noticed a color cast on your photos, like blue, orange or even green, you may want to begin setting a custom white balance. Not only are these color casts unsightly, they can be hard or impossible to remove from some images. With a custom white balance your colors can be more true to life. The process is simple and quick for any Rebel XTi user.
Turn your camera on and make sure the dial isn't set to any of the choices other than a preset Canon setting. Any setting between the green box and the "M" on the dial should work. If you're accustomed to working in Manual mode, feel free to do so for this exercise, but you may want to start with a more basic mode if you are just learning how to use the camera.
Take the lens cap off your lens and take out your white balance card. You can either buy a card specifically made for setting white balance or an Expodisc from your local photography store. However, many amateur photographers have had great success using a white coffee filter or the nearly opaque white lid like those found on frozen whipped cream containers.
Hold your white balance object in front of your lens making sure to hold the tool at an angle that does not create shadows. It's also important to take your test picture under the same conditions you plan to take the other photos. Setting a white balance in bright, natural light and then walking to the opposite corner of the room and taking a picture with tungsten lighting doesn't produce accurate results.
Focus on the white balance card using manual focus. When the white object fills the center of the viewfinder, take a picture.
Select the "Menu" button on the left side of the camera's screen. Scroll to the second camera setting menu and then down to the "Custom WB" option. Press the "Set" button. This opens the pictures stored on the camera's disk.
Scroll through your pictures and select the photo you just took of your white balance object.
Press the "WB" key. This is the lowest key on the right-hand side of the camera's screen with the other quick-control functions. Scroll over until you can see the custom white balance option. Press the shutter button down halfway to select.
Take pictures with your new custom white balance setting. You should notice when you review the pictures the colors appear more true to what they looked like when you took the pictures. This is because you have told the camera what white looks like where you are shooting. With this method you can reduce the amount of post-processing you need to perform on your photos.