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Bernardo Alvarez
2022-03-23
Applications

Lumher illumination especially for OCR

If you usually work in the world of machine vision, you will know that one of the projects that usually resists more often are those related to the reading of characters or OCR ("Optical Character Recognition"), in this type of projects, It is usually necessary to study the lighting to be used and the relative position of the camera to achieve an illumination that maximizes the contrast between the characters and the background of the piece, since in many cases, if not all, the material of the letters to be recognized is the same as the piece itself, so the contrast between them is minimal, which hinders the realization of the OCR.
Lumher illumination especially for OCR

Getting started

Examples made in 3D printing for the realization of character reading

One of the tools that facilitates our work in this type of projects is the use of pre-filters (available in the Smart camera Sensopart from the Advanced model) such as Sobel, Dilation, Erosion, Multiplication and Inversion filters among others, which help us to obtain an image with higher contrast by sacrificing cycle time. However, in some projects, either by the material of manufacture of the part or the cycle time required, we can not use this type of tools, so we have to look for the solution in a special tool found in the All-ROUND cameras, the Multi-Shot.

Image of an All-Round camera with different types of multishot illumination

Discover the multi-shot

Multi-shot is a feature of the Sensopart ALL-ROUND cameras, which allows 4 photographs to be taken in sequence and combined into one, each of these 4 photographs is synchronized with the lighting of a quadrant of the luminaire, obtaining maximum contrast between elements that, although they are of the same material, have relief.

From Lumher, we have developed a perimeter luminaire compatible with the Multishot system of Sensopart, this luminaire, created from the current product P4D, allows the orientation of each of the segments independently, increasing the flexibility and potential of the tool and synchronizing the lighting of each of the sectors with the Smart Camera.

Practical case

Separate images of each of the light bar shots As can be seen in the image above, the camera takes four photographs coordinated with the lighting of each of the quadrants of the luminaire. In this way, it can detect where there is a relief by analyzing the contrast between lights and shadows, enhancing this difference and joining the four photographs into a single one by means of different logarithms that can be selected through the interface to obtain the best result.

As a result, a substantial increase in contrast is obtained in the elements with relief, as well as homogeneity of light, significantly reducing the brightness, making it possible to read characters. The cycle times of this example are around 0.5s, which allows a reading of about 7,200 units/hour, the reliability in reading characters is over 95%, which ensures a robust reading.

The cycle times of this example is around 0.5s, which allows a reading of about 7,200 pcs/hour, the reliability of reading characters is above 95%, which ensures a robust reading. Camera reading result using Multishot and Lumher luminaire without using filters

Our solution

We encourage you to take a look at the lighting products specially designed for artificial vision, where you will find from front lighting through Rings, perimeter lighting and backlight, we also have different wavelengths and polarizing filters integrated into the product to avoid any kind of glare.

Additionally, the entire range of vision has different operating modes (continuous, pulsed and strobe) without the need for a controller to ensure the necessary light in any type of project.

If you have any questions or want more information about the type of lighting we can offer do not hesitate to contact us and we will be happy to help you,

See you in the next blog entry!

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