An unimposing little grey card, that is how the WhiBal G6 presents itself. On the front a black-and-white sticker, on the back another with technical data; a couple of holes. This easy to use, handy, durable reference card for digital imaging was developed by the American photographer Michael Tapes.
                            

We all know by now that light comes in different colours. Most of the time we perceive it as white regardless if it is sunlight, incandescent, photographic flash, even gas discharge lamps or fluorescent's seem to give bright white light. This only shows how excellent human eyes and brain work together; while the former records the colour shift, the latter corrects it so we recognize what we are used to. Rarely do we take note, our brain is well adapted to deceive us as we deceived film with filters. Digital sensor, like our eyes or film, ingest everything, it takes complex circuits to correct colour shift if we want to have natural colours in our photos.
                            

In past times, when we used film, we had to know the characteristics of our emulsions as well as those of the light sources we took photos under. Most commercially available films were adjusted towards an averaged daylight source. This worked very well with negatives, which are automatically corrected in mass developers. Transparencies, on the other hand, came out with slight to strong shifts to yellow, blue or orange depending on time of day. It became really bad with fluorescent's and incandescent light.

Incandescent light bulbs have a warm, orange light, which is easy to correct

Filters to correct these colour shifts were the answer for film. But video cameras showed us that an in-camera solution was possible: read a reference into it. While early cameras needed to record off a white paper or a special lens cap, today’s digital [still and video] cameras use sensors to measure environmental light during recording. Like the human brain they calculate what the correct colour should be. In automatic mode they use, like humans, pre-saved values and comparisons of the three colour channels Red, Green and Blue – any big differences are interpreted as colour shifts. This works well over a wide range of colour temperatures but breaks down under some conditions; Nikon, for instance, limits the use of automatic white balancing to 3500-8000 °K.
                            

This leads many photographers to the use of the custom white balance their cameras offer: You hold a traditional grey card or white sheet of paper in front of the camera, catching the same light as the photographic subject. Then you let the camera [more or less easy depending on make and model] measure the light, save the value and shoot away. It is an archaic method from olden days of film, when professionals started each roll of film with a reference shot of a grey card for colour and exposure, but still useful today in case you shoot an instant format like JPEG or TIFF, where later corrections are problematic.
                            

Using your camera’s RAW format makes everything much easier. Since this format saves the actual sensor data in digital form, no in-camera image editing applied, you can correct for any difficult light situations later on your computer unhurriedly. You only need some software, the RAW converter. Instead of discretionary changes to the white balance, relying only on your eyes and a hopefully calibrated and profiled monitor, you should still use Michael Tapes’ WhiBal. It allows you a one-click correction of colour to neutral.

A reference photo of your WhiBal, one click with the white balancing tool and your pictures shine in the correct colours.

Michael Tapes offers various sizes of WhiBal, the smallest being the Pocket, which comes with a lanyard and quick release. It is the vademecum card, offering enough grey area for easy white balancing. If your photography is more stationary, i.e. in a studio, the aptly named Studio card or the even bigger Reference may be a more comfortable choice. They are not made of paper or cardboard as traditional grey cards but from a foamed-in cellular material, making them very durable and scratch-resistant. They even swim in water.
                            

A black-and-white sticker on the front helps to determine the black and white point if you are shooting JPEG or TIFF. A sticker on the back is a cachet, showing typical RGB values of the cards; every single card is measured with a high-tech colorimeter, and the differences between the channels are usually much smaller than the sticker shows [refer to www.RAWWorkflow.com for the technical details]. The manufacturer guarantees a card that is as neutral as you can get, quite within any tolerances your camera has – or your eyes, for that matter.

How to
                            

1. Let your camera save in RAW 
2. At the scene hold the WhiBal in front of the lens and take a photo. Just make sure it reflects the actual lighting of your photographs.
3. If the light changes take a new WhiBal shot.
4. At home load your photos into your RAW converter of choice, open the WhiBal picture, click on the grey area to get the colour temperature
5. Save the values and apply it to all those photographs with the same lighting conditions.
6. If you have more than one WhiBal reference photo for differing light, do the same for those and associated pictures.
                            

It does not make any difference when you took your reference shot as long as the light on it is he same as on the concrete shoot. For interiors in buildings featuring the same light – museums, churches, gymnasiums etc. – you can take the WhiBal photo in advance or days later if you want.