When shooting trace material evidence, what scale should light-colored objects choose?

When shooting trace material evidence, the proportion of black and white is selected for light-colored objects. According to relevant data, dark objects use the scale of white scale on the black background, light objects use the scale of black scale on the white background, full-color and blind negatives use the scale of black and white, and color negative and digital photos use the scale of color. When taking off-angle photos of trace material evidence, put a square ruler beside the trace material evidence.