Machine Vision Basics 04 - Lighting Fundamentals

Summary

This script discusses the importance of lighting in machine vision applications, covering the visible spectrum, UV, and infrared light. It explores various lighting techniques, the impact of light on objects, and the use of color and polarizing filters to enhance image quality and contrast, ultimately improving inspection accuracy.

Takeaways

• 🌈 The human eye can perceive colors from the visible spectrum ranging from 400 to 700 nanometers, situated between ultraviolet (UV) and infrared (IR) light.
• 🛠️ Machine vision applications can utilize both the visible spectrum and extend into UV and IR for tasks that require special lighting sources, including reading UV and IR barcodes.
• 💡 Third-party lighting is essential for successful machine vision applications, especially when working beyond the human visible range, and ambient light is not recommended due to its inconsistency.
• 🔆 Different illumination techniques, such as bright field, dark field, back lighting, diffuse dome, structured light, and coaxial lighting, interact with objects in various ways, affecting the outcome of vision inspections.
• 📸 Lighting can impact how objects appear in machine vision by absorption, reflection, transmission, scattering, or a mix of these, highlighting the importance of selecting the right lighting technique for the task.
• 🎨 Color cameras can be used for specific applications but may sacrifice resolution and speed compared to monochrome cameras; understanding color theory, such as using complementary colors for contrast, is crucial.
• 📉 Monochrome cameras often use bandpass filters to enhance contrast and are suitable for applications involving common LEDs, UV, and near-infrared wavelengths, offering an alternative to color cameras.
• 🌀 Polarizing filters are compared to sunglasses, reducing unwanted reflections and glare, and are particularly useful for inspecting transparent objects, smooth surfaces, or those with liquid or oil.
• 🌟 The choice of lighting color can significantly affect the visibility of features in monochrome images, emphasizing the importance of selecting the appropriate third-party light for accurate inspections.
• 🔍 High-resolution color inspection with a color camera involves a Bayer filter that interprets the intensity of red, green, and blue light passing through a 2x2 grid of pixels to determine color.
• 🚫 Using the wrong color of third-party lighting with a monochrome camera can lead to images that appear identical, even though they may represent different features, underlining the necessity of proper lighting selection.

Q & A

What is the range of visible light wavelengths?

The range of visible light wavelengths is from 400 to 700 nanometers, covering colors from purple to red.

What are the applications of UV and infrared light in machine vision?

UV and infrared light can be used in machine vision applications that require non-visible light sources, such as reading UV and infrared barcodes.

Why is ambient room light not recommended for machine vision applications?

Ambient room light is not recommended because it typically changes constantly, leading to inconsistent results and making it difficult to achieve repeatable success in machine vision tasks.

What are some common illumination techniques used in machine vision?

Common illumination techniques include bright field lighting, dark field lighting, back lighting, diffuse dome lighting, structured light, and coaxial lighting.

How does bright field lighting interact with objects?

Bright field lighting causes light to bounce back up into the camera, which can help in highlighting features on the object being inspected.

What is the effect of dark field lighting on the object being inspected?

Dark field lighting reflects light away from the camera, making it useful for highlighting edges and contours of objects by creating a contrast between the object and the background.

How does backlighting affect the image quality in machine vision?

Backlighting can create a silhouette effect, which is useful for presence/absence checks but may not be suitable for precise measurements due to its fuzzy edges.

What is the purpose of using a color camera in machine vision?

Color cameras are used when color information is crucial for the application, such as in color inspection or when specific color features need to be highlighted or distinguished.

How does the use of a color filter affect the image captured by a monochrome camera?

Color filters on monochrome cameras can enhance contrast and help in distinguishing specific features by filtering out certain wavelengths of light, similar to how polarized sunglasses reduce glare.

What is the role of a polarizing filter in machine vision?

Polarizing filters reduce unwanted reflection or specular glare, which can be beneficial for inspecting transparent materials, smooth surfaces, or objects covered with grease or liquid.

Why are bandpass filters used in machine vision?

Bandpass filters are used to enhance the contrast for viewing specific features, particularly in applications involving UV and near-infrared wavelengths, by filtering out unwanted ambient light.