Imaging Sensors : Difference between Monochrome Sensor and Color Sensor

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A camera sensor is a piece of hardware inside the camera that captures light and converts it into signals that result in an image. Millions of photosites, or light-sensitive spots, referred to as Pixels make up the sensors, which capture what is seen through the lens.

In this article, we examine the key differences between each of the types of sensors and the impact they have on the final image.

What is a Digital Imaging Sensor?

Images are captured using digital sensors, in which photons of light are gathered by arrays of wells called pixels. Like a grid of buckets, digital sensors capture light in an array of pixels. When an exposure starts, these are unveiled and the photons are collected; when the exposure ends, they are read as electrical signals, quantified, and stored as values in a digital file. pixels often use filters to store only one colour at a time in order to assess colour.

The pixels measure the amount of light. For pixels to achieve colour, they must also distinguish and record values separately for each colour. This arrangement of colour filters makes sensors unique.

What is a Pixel?

Generally, a camera sensor is composed of millions of holes known as photosites or pixels. A single photodiode that records a brightness value is present at each pixel. When the shutter is opened at the beginning of the exposure, light photons hit the lens and travel through the lens aperture before some of the light is let through to the camera sensor. After the photons strike the sensor surface, they pass via a microlens that is mounted to the receiving surface of each pixels to help focus the photons there, followed by a colour filter (such as a Bayer one) that is used to help identify the colour of each pixel in a picture.

Let’s now examine the two different sensor types.

  • Monochrome sensor
  • Colour sensor

Monochrome Sensor

Monochrome sensor allows all wavelengths of light into each pixel. Essentially, the numerical value stored represents how much light is present. Color information cannot be distinguished and measured by it because it does not have the necessary architecture.

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Monochrome sensors, in contrast to colour sensors, record all incoming light, regardless of colour, at each pixel. Red, green, and blue light are all absorbed, so each pixel receives up to three times as much light. So, the information a monochrome sensor provides is luminescence information.

The advantages of monochromatic sensors include decreased image noise at equal ISO rates.

Bayer Pattern

The Bayer Pattern is the most successful colour filter array. The RAW Bayer sensor has the same fundamental design as the monochrome sensor. It does, however, include an extra colour filter array as part of the microlens.

Primarily, it converts a monochrome sensor into an RGB or colour sensor. It is an extra layer that is placed on top of the monochrome sensor.

Color Sensor

Utilizing something known as a “colour filter array” (CFA), color sensors work by selectively capturing one of many primary colors at each pixel in an alternation pattern. Each pixel uses CFA to alternate between several primary colors. Bayer arrays are the most common CFA pattern. The Bayer array image has twice as many pixels that represent green light. This is because the human eye is more sensitive to shades of green and it more closely relates to light intensity. Color camera modules are based on raw Bayer imaging sensors.

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Bayer sensors follow a simple strategy. Red-green and green-blue filters alternate in the Bayer pattern. Each pixel captures alternating red, green, and blue colors. The amount of green pixel collected is twice that of the other two colors. Through a process called “demosaicing” – also known as “debayering”, these images are then intelligently combined into full color pixels.

Colour vs Monochrome

Monochrome camera sensors can capture more detail and have higher sensitivity than colour sensors. Another advantage is that monochrome sensors have less predictable highlight clipping. Clipping in color can occur in only the red, green, or blue channels, but clipping in monochrome is an all-or-nothing operation. In practice, this means that photographs have a somewhat higher acceptable dynamic range, especially as monochrome shadow noise is usually less irritating than color shadow noise.

The existence of a Bayer filter in a color camera may cause the system’s optical resolution to function inadequately. Additionally, the demosaicing algorithm itself has the potential to produce mistakes in color reconstruction. Monochrome sensors need not necessitate demosaicing to achieve the final image, in contrast to color sensors. In essence, the values at each pixel are exactly the values that were captured at each pixel. Monochrome sensors can thus provide a little higher resolution and at comparable ISO speeds, there is less image noise.

Whereas any colour that does not fit the pattern is filtered out, a necessary but unwanted side effect of CFAs here is that every pixel only effectively receives around one-third of the incoming light. By contrast, any red or blue light that strikes a green pixel won’t be captured.

No additional interpolation or processing is required with monochromatic sensors. Thus, monochrome cameras are easier to develop. We can always get monochrome data from color data, but not vice versa. Color sensors, on the other hand, require additional processors and circuitry to produce accurate color data. Therefore, designing a color camera is more difficult than developing a monochrome camera.

Wrapping Up

Depending on the intended usage, it is important to keep in mind that not all benefits will be possible. Monochrome sensors offer a higher quality, yet they are less flexible than color sensors. For example, color can always be converted to monochrome afterwards. Furthermore, with color capture, any arbitrary color filter can be applied in post-production to customize the monochrome conversion, whereas monochrome capture is irreversible when a color filter is mounted on the lens. Overall, monochrome capture always produces superior results if output flexibility is not needed.

As a result, you must be aware of those sensors in order to select the appropriate one among these two. Still confused? We can assist you in understanding.

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Cheers!

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