How to calculate the color uniformity of the ambient light?

For selfluminous products such as ambient lights, we recommend using L2(Lxy) to calculate color uniformity.

As an atmosphere lamp created by the atmosphere in the car, the uniformity of its brightness and color will undoubtedly have a significant impact on the visual perception.

Regarding the measurement of brightness and uniformity, we wrote a series of articles last year. Today we will take a look at how to evaluate the color uniformity of ambient lights.

Of course, our evaluation methods here are all based on the chromaticity distribution chart obtained by the imaging colorimeter.

The picture below is a color distribution image we measured through LMK Color. We want to test the color uniformity of this light guide.

Horizontal screen is recommended here:

The so-called color uniformity is the difference of colors in different positions, therefore, color difference is the basic data.

Labsoft software provides quite a wealth of color difference analysis functions. Under the Evaluation menu, there are two algorithms:

Color difference between images (the color difference distribution between the image and the image, that is, between the two images, the same position, the color difference is calculated between the two images before and after)

Color difference to a color (all points on the image are calculated for the same color)

The first method is suitable for comparison with standard samples. This scenario is not used much. Obviously the second method is more suitable for our evaluation of ambient lights.

After entering, we see the specific parameter settings of color difference:

The first is to choose the color difference definition. There are many options, dE (Luv), L2 (Lxy), dE (Lab) and so on. See the specific formula at the end of the article. For self-luminous products such as ambient lights, we recommend using L2(Lxy).

Here we have marked an area on the chromaticity diagram, namely the No. 1 rectangular area. The color of this area is used as the reference color, and all pixels are calculated for color difference with it. To use this function, you can click From Marked Rectangle in the lower right corner of the dialog box, or you can define and enter a color value to calculate the color difference.

Another key parameter is the minium luminance in the upper right corner. A luminance threshold can be set. Only when this threshold is exceeded can the color difference calculation be performed to prevent the color difference calculated in other areas from causing poor visual effects of the resulting image.

The final calculated result is a color difference distribution map, each pixel has a value, save it under the luminance image, or under other luminance maps.

Original image:

Color difference chart:

Color difference scale:

The darker the color, the smaller the color difference. Then, in this color difference distribution diagram, treat it as a brightness image for uniformity analysis, such as the maximum and minimum color differences, and the average color difference.

To evaluate the color of the ambient light, after selecting the range, provide different algorithms to match different scenes:

The following algorithms are especially recommended

Color Symbol Object

The brightness threshold can be used to separate the light-emitting part in the area from the background, and then calculate the average color of the light-emitting area, the maximum and minimum brightness, and the uniformity of brightness.

Chromaticity line (area) Diagram

Display the chromaticity coordinates of the pixels in the selected area on the chromaticity diagram, you can intuitively see the degree of dispersion of the color distribution, the more concentrated, the better the color uniformity, on the contrary, the poor color uniformity.

Attachment: Color difference formula: