Enhancing Monochrome Imaging with Optical Filters: A Practical Demonstration

In industrial image processing, every detail counts – especially when working with monochrome cameras. While these cameras offer high sensitivity and resolution, they often struggle with contrast when objects or materials share similar brightness levels. This is where color filters come into play.

To illustrate the impact of filters in a hands-on, relatable way, we conducted a simple experiment using colored document folders as test objects and compared the results with and without optical filters.

The Setup:
We used a monochrome industrial camera to capture three different colored folders (blue, red, and yellow) placed side by side under identical lighting conditions. The original image without a filter showed poor separation between the different colors is – a typical challenge in monochrome imaging.

^{Use mouse over to see the original image in color.}

Filter 1: BP 660-60 – Enhancing Red

By introducing a bandpass filter centered around 660 nm with a 60 nm bandwidth (BP 660-60), we significantly increased the visibility of the red folder. The filter blocks most other wavelengths, allowing primarily red tones to pass through, which results in high contrast for red objects in monochrome imaging.

Filter 2: NBP 450-40 – Isolating Blue

Next, we used a narrower bandpass filter centered at 450 nm with a 40 nm bandwidth (NBP 450-40). As expected, this filter enhanced the contrast of the blue folder, while suppressing other colors in the scene. The result: the blue object stands out clearly against its surroundings.

Filter 3:  Polarizing Filter – Revealing Hidden Contrast

In a second test, we used a polarizing filter to increase the visibility of white text printed on a glossy film. Without the filter, glare and reflections made the writing barely visible. With the polarizer in place, reflections were suppressed, and the bright text became clearly legible.

This example highlights another important application of filters in machine vision: polarization filters are essential when dealing with reflective surfaces, such as plastic, glass, or metal. They help reduce glare and enhance surface details that would otherwise be obscured.

^{Use mouse over to see the original image without filter.}