Boost Colour Camera Capability with Advanced Optical Filters

This is the fourth editorial in a series of five which discusses MidWest Optical Filters for machine vision and how they can be used to improve results, simplify design or reduce costs.

Part 1 - Five Technical Benefits of Midwest Optical Systems Bandpass filters with Monochrome Cameras

Part 2 - Advantages of combining Monochrome cameras with MidWest optical filters

Part 3 - Boost Colour Camera Capability with Advanced Optical Filters

Colour cameras are used to achieve natural colour rendering, equivalent to what the human eye can see. However, the sensitivity of the sensor and spectra of the light source being used can significantly affect the colour or image quality. Using a filter is the easiest, most cost-effective way to:

• Achieve accurate colour rendition
• Reduce specular glare
• Reduce light intensity
• Regulate exposure

Colour cameras are a popular choice for photography, license plate recognition, security, surveillance and agricultural inspection and can be helpful in any application where accurate colour inspection is required.

Need help selecting the right bandpass filter? Speak to the experts at Adept Turnkey.

Neutral Density (ND) filters are primarily used for exposure control by limiting excessive light that could otherwise overwhelm an imaging sensor or subject. By uniformly reducing light intensity, ND filters help preserve image resolution, prevent saturation and enable greater control over depth of field. 

Day and night imaging applications often require accurate colour reproduction during daylight conditions and reliable near infrared imaging at night using discrete IR illumination. Dual bandpass filters provide an effective solution by transmitting visible light along with a narrow, defined band in the near infrared spectrum that matches the wavelength of the IR light source. 

Dual bandpass filters enable seamless transitions between day and night imaging while maintaining accurate colour rendition and high image contrast. 

NDVI

Dual bandpass filters and colour cameras are increasingly used in agricultural and forestry applications including crop monitoring, process control, mapping and vegetation health assessment. A widely used analytical method in these applications is the Normalised Difference Vegetation Index (NDVI), which evaluates plant health by comparing reflectance in the near infrared and visible spectra.

NDVI = (NIR − VIS) / (NIR + VIS)
Healthy vegetation absorbs visible light, particularly red wavelengths for photosynthesis, while reflecting near infrared light to prevent overheating. This behaviour produces high NDVI values. In contrast, stressed or dying vegetation reflects more visible light, especially red, and absorbs more infrared radiation, resulting in lower NDVI values.

Traditional NDVI systems typically rely on multiple cameras or sensors with dedicated optical filters to separately capture red and near infrared data. While effective, these systems can be expensive and heavy. Recent advances, along with the availability of lightweight unmanned aerial vehicles and converted consumer cameras, have increased interest in single camera NDVI solutions using dual bandpass filtering and image processing algorithms.

Consumer cameras are generally optimised for aesthetic imaging and often have limited spectral band separation, reduced dynamic range and automatic exposure or white balance functions that are difficult to control. Once the internal infrared blocking filter is removed, overlap between colour channels can distort NDVI calculations.

Dual bandpass filters with narrow, well defined passbands and sharp spectral cut on and cut off characteristics have proven effective in overcoming these limitations. When combined with cameras that allow manual exposure and white balance control, these filters can deliver NDVI performance approaching that of significantly more expensive multispectral imaging systems.

Lens Protection

Protective filters play an important role in safeguarding lenses, filters and lighting systems from impact, dust and harsh environmental conditions. Manufactured in glass or acrylic substrates, these filters act as a protective barrier that helps preserve the performance and longevity of valuable optical components.

In addition to physical protection, protective filters block interfering ultraviolet radiation that can degrade image quality. Optional anti reflection and anti abrasion coatings improve transmission efficiency and durability, making these filters suitable for demanding industrial environments.

Acrylic protective filters offer additional flexibility, as they can be custom laser cut and configured to fit a wide range of lenses, cameras, enclosures and lighting assemblies while maintaining optical performance.