IN ADDITION, KEYENCE'S VJ SERIES

Defects that do not appear in the image cannot be detected by any algorithm.
Therefore, it is very important to visualize defects.

Appearance defects can be divided into two main types.
Shape defects, such as scratches, and color defects, such as stains.

The former appears in the image when the reflected light from the light source enters or does not enter the camera depending on the angle.
If the surface is highly glossy, the reflected light must be positioned close to the normal reflection, otherwise the light reflected at the defect will not enter the camera, and the white light will not be visible unless it is right next to the reflection of the light source. Therefore, the visual inspector fanned by hand to focus on the side of the light source.
If the surface has low gloss, it will appear white when light from a particular direction is reflected and enters the camera; conversely, it will appear black when the reflected light is reduced. The contrast is not high because the scattered light is also strong, but if the direction of the light source is changed, it becomes noticeably whiter or blacker, which can be easily visualized.
However, defects with low gloss and smooth bumps are extremely difficult to visualize because there is almost no change in the image even if the direction of the light source is changed.

The latter is considered to be an anomaly in the way light from the light source is scattered on the surface. A change in the wavelength of scattered light = a change in color. This does not occur on an object with high gloss and almost no scattered light. Also, because of the scattered light, there is almost no change in the image even if the direction of illumination is changed.

I had empirical knowledge of this.

WITH THIS KNOWLEDGE, WE LOOK AT KEYENCE'S VJ SERIES LINEUP.

• LumiTrax Orthorectified mode for high-gloss objects. While changing the direction of the light source, multiple images are taken by aiming right next to the reflection of the light source. Since a considerable change in luminance is produced depending on the direction, shape defects can be captured with considerable contrast.
• LumiTrax is used for general shape defects; it can acquire shape images of areas where luminance changes depending on the direction of the light source. Images can be acquired by eliminating the effects of scattered light-dependent "color" that does not cause luminance changes. The image is similar to that of a visual inspector turning and inspecting.
• Low-gloss, gently convex and concave defects are pattern projections. This type of defect is impossible to visualize with normal lighting methods, and the only way is to image it as a three-dimensional object. However, it is a defect that is quite difficult for even a human to see, so it is a mystery whether this level of visual inspection is necessary.
• Color defects are multispectral. However, most of the color defects without shape defects should be fulfilled as a function of the object. If we consider that it is enough to remove only the noticeable ones, there may be little need for color detection with such high accuracy.

For visual inspection applications, LumiTrax is probably the only choice. It is clearly on a different level from existing cameras and lighting.
It can almost solve the problem of defect visualization.

The problem is "too visible". I think it is an algorithmic game from here.