How to measure light with grey card and get correct white balance?

Put the gray card on the object to be photographed, and use the spot metering function of the camera to photograph the gray card.

If your camera has the function of custom white balance, you can import this gray card photo as the standard of custom white balance, so that the tone of the photo taken in the same light environment is basically accurate. Of course, the exposure compensation should be adjusted according to the individual's shooting intention.

The gray card is used to set the manual white balance. The usage method is simple, that is, after setting the custom white balance, put the gray card close to your subject and take a photo of the gray card, and the camera will set the custom white balance according to the photo of the gray card. The principle is also very simple, that is, the automatic white balance of the camera is not accurate. Then tell the camera what an accurate white balance looks like. How to tell? Just tell the camera that it is gray, and you can set this color to gray in the image.

It doesn't matter what shooting mode you choose and whether the exposure is accurate, because the same gray has different color expressions in different lighting environments. The exposure camera will do its own calculations. If you think it is inaccurate, use exposure compensation to adjust it. Gray cards are used to adjust colors. If the color of the camera is not accurate, you can tell the camera that the color is gray with a gray card.

Many times you can set the white balance with pure white paper or cloth without gray card. For example, in the incandescent lamp environment, automatic white balance shooting will turn yellow, and white paper will be made into yellow paper. At this time, the custom white balance tells the camera that it is white, and the camera will make corresponding adjustments, and the white balance will be accurate.