[Cause]
There are too few colour pixels in the specified area. This may be due to:
1. The overall darkness of the colour within the given area.
2. The colors throughout the specified region are vignetted.
3. A portion of the designated area is mirrored.
4. Specular reflection from the lighting in part of the specified region makes it appear white in the image.
5. The colour on the image differs from the colour of the object to which the measure is made.
[Countermeasure]
For their respective reasons, the response is as follows:
1. Increase the lighting intensity or lengthen the exposure time.
2. Please reduce the amount of light or exposure time.
3. Change lighting configuration to avoid shadows.
4. Change the lighting arrangement to avoid specular reflection.
5. Use white lighting and reduce brightness unevenness throughout the field of view when arranging the lighting.