Today Damien Franco is guest posting. Below he provides a GREAT explanation on how to use a gray card with auto white balance.
What is Auto White Balance (AWB)?
Simply put AWB is a setting in your camera's menu that allows the camera to use a "best-guess" algorithm to decide which color temperature to choose by measuring the light falling onto the subject/subjects in your scene.
With very advancement in camera technology we get better results from this algorithm. This is a good thing and it can save you a ton of time when it comes to post processing your photos not to mention the advantage of ending up with images that are truer in color to the scene that was originally captured.
Here are three steps that will help you get truer colors from your photos and save you tons of time in the process.
1. RAW is your friend. While not every digital camera comes with the ability to shoot in RAW most of the newer and more expensive ones will. The real benefit of shooting in RAW is that you end up with an image file that has much more information than a JPG. This ultimately translates to a wider range of color correction and the ability to get truer colors with more vibrancy and tonal range.
Shoot in RAW. Yes, it takes up more space. No big deal really, hard drives are getting cheaper and cheaper by the day and external hard drives are a snap to set up.
While it can be a little intimidating to begin the transition to shooting in RAW it's not really much different if you have a good post processing work flow.
2. Gray cards rock. Why? It's because your camera actually wants to see that gray card. It craves it. When your camera is looking for something to use as a base for its algorithms (that super split second when it's balancing exposure and color) it's looking for a neutral 18% gray in your scene as a base. If you don't have a neutral 18% gray in your scene it will find something as close as possible and compensate exposure and color balance.
This is why we can see dramatic color shifts in the same room with the same lighting and the only thing that's changed is the person in the photograph. The camera is reading a very different scene in a bridal portrait with a white dress compared to a groom in a black tux. Same room. Same background. Same lighting. Different results.
Do you absolutely need a gray card? Not really, but it helps in many situations. I use a gray card when I know I will be in one room with consistent light for many shots. I don't use a gray card when I'm running around town on a photo-walk or shooting images of my crazy kiddos. It's good to have one handy though at all times.
Shooting an image of the gray card in a consistent lighting situation allows you to have a reference point and it only takes a second. This'll come in handy on the next step.
3. Batch processing will free your life. There are a number of image editing software programs out there. I'm not here to tell you which one is better (this is always a personal preference) I will refer to Adobe's Lightroom because it's what I'm most familiar with.
Simply open the image that contains the gray card and adjust the white balance (WB) using the dropper. You should get an instantly great result with neutral or "true to life" colors. At that point you can "fine tune" a little if needed. Then you save those settings as a preset. Select all of the other images that were shot in that same lighting scenario and sync them with that preset. BAM! You just adjusted the lighting on several/dozens/hundreds/thousands of images with lightning quick precision. Much better than adjusting every single image one at a time. Sure, it's possible that exposure may need to be adjusted on some of the images, but the skin tones will match much more closely. You won't have one person looking seasick in one image and another with a bad case of jaundice. Nice.
Remember that our eyes are easily fooled and adjust to color temperatures around us. Having a properly color calibrated monitor for your computer will help to ensure that what you're seeing on your screen is accurate.
Please be sure to visit Your Photo Tips. It is a GREAT resource for photographers.