The neutral grey card is one of the simplest, most useful and yet most neglected of photography tools.
It requires no batteries, can be used without any complicated instructions, works in black and white or colour, day or night, in coal mines or deserts, yet often stays at home unused, unloved.
The neutral grey card originally came from the printing industry. A printer would look at the neutral grey card and compare it with a sheet of newspaper ( back when newspapers were all type and no illustrations) and see if they were applying an appropriate amount of ink onto the page. Too dark = too much ink, etc.
In the earlier parts of the 20th century when devices were being invented that could measure the amount of light, the neutral grey card started to take on another use.
Early photo scientists started to measure the relative brightness of scenes so that a device could be made to judge appropriate exposure for photography. This resulted into light meters and the magic of sensitometry.
We know that light meters help us in photography by suggesting appropriate exposure settings based upon camera settings such as ISO, F stop, shutter speed, and the relative brightness of the scene. The light meter then gives us what it calculates to be the optimal exposure settings.
Sensitometry is the science of measuring the relative sensitivity of film or electronic devices to varying light conditions and contrast.
Huh? Back when film first started becoming commercially made there were the inevitable advertising claims and lies about the sensitivity of various brands of film and plates.One brand would claim more sensitivity than another, one developer would give faster film speeds, etc. Standards needed to be set.
One of the earliest standards was ASA, American Standards Association. Their test was to expose film on the longest day of the year, at high noon, in Washington DC and a clear sunny day. At f 16. The shutter speeds were varied and the ASA was determined by the shutter speed needed to provide a negative that could make a high quality print. As we might know, an under exposed negative gives a print with muddy looking shadows, and overexposed negative gives a print with highlights with no details.For example, should the best exposure be 1/125 then the ASA was 125. 1/25 and the ASA would be 25.
Just to make things fair, a standard formulation of developer was used. Coincidentally, no photographer actually uses this developer in their daily work, there are better developers available.
As time went on, electronic devices called densitometers were created that can measure the amount of light transmitted through the film or the amount of light being reflected off an object. And, of course, someone had to formalize all this and created the science of sensitometry.
Today, film speed is determined by the amount of exposure needed to give a certain amount of density on the film with a slope of 0.7 ( logarithmic just to leave you more confused). And that certain point happens to be of a neutral grey card.
After going through all that, your camera’s light meter is designed to give its exposure suggestions based upon it being designed to assume the whole world is painted 18% neutral grey. Your 1960’s through 1980’s cameras are all made to their standard as far as the light meter is concerned. Newer cameras started to meter (more properly measure) the light in various parts of the photograph, and then analyzed the scene brightness to adjust its metering recommendations.
But what is this neutral grey card? It is merely a piece of cardboard that has been printed with grey ink or paint with a reflective amount of 18% and has a neutral colour cast. Pulling out my densitometer, I measured it for RGB reflectivity of 128, 128, 128. that is a neutral colour with equal amounts of Red Green and Blue and exactly in the middle of the range for digital photography.
Jumping to today, open up Photoshop or any other somewhat advanced photo editing program, get out the colour picker and scroll over any colour photo. Make sure that you are using the RGB mode. That will tell you the relative colour balance of any pixels or group of pixels in your scene.
Why would we use a neutral grey card? To get a better starting point to exposure and colour balance.
To use. Place your neutral grey card into the middle of the important part of your scene. If on manual, set the exposure, if not shooting on manual adjust the exposure to match the grey card readings. take a shot of the grey card and some of the scene, then remove the grey card and take your photo. Important points, don’t cast a shadow onto the card, make sure that the card is facing the camera, and should you be adjusting your focus use that focus when taking the shot of the neutral grey card.
You might also want to set your manual white balance, read your camera manual.
Check your display screen just to make sure you have not made a grievous error.
When you have finished shooting that scene, review the photo on your computer. Use the White Balance Selector ( in Lightroom its the eye dropper W) scroll over it. Observe the RGB values and then click on the neutral grey card. The numbers should be equal values and and near 128 assuming you used the suggested exposure settings. I usually find the colour balance to become much more neutral with a more realistic colour balance.
The biggest advantage to this is to correct any colour imbalances. Such as fluorescent lights, under trees, mixed lighting, cheap led lights.
Q? But I like using Instagram looks or video LUTS on my photos? Great, but if you value a consistency of look, get your photos to a more standard look before hand.
Q? But I shoot video. This all applies to you, but you might also want to also use a white card for colour balance or to avoid highlight clipping.
Where do I get a neutral grey card? The old stand by, Kodak no longer seems to make them. But, Delta does. About $20. A better choice is Whibal. https://www.outdoorphotogear.com/collections/whibal The cards that they sell are a hard plastic, waterproof and durable.
There are also more advanced devices such as Spyder Color Check https://www.datacolor.com/spyder/
Sal Cincotta has a great video about how he does colour matching
I hear your cries, you are broke after buying the new camera with the 600mm lens and the trip to photograph penguins. No problem.
I went to the local paint store and ‘liberated’ some paint swatches. Using a densitometer I tested and determined that these should work.
Canadian Tire “Iron Work”
Home Depot “ Seal Grey”
Home Hardware “Subtle Shadow”
They are all very close to Neutral Grey. Lastly, the sample strip D36 at Home hardware has the “Subtle Shadow” and a variety of lighter and darker paint swatches. And, be nice, buy something lest they think you are just another cheap photographer.