{"id":3954,"date":"2024-05-24T15:06:47","date_gmt":"2024-05-24T19:06:47","guid":{"rendered":"https:\/\/www.1stvision.com\/machine-vision-solutions\/?p=3954"},"modified":"2024-05-24T15:06:47","modified_gmt":"2024-05-24T19:06:47","slug":"monochrome-light-better-for-machine-vision-than-white-light","status":"publish","type":"post","link":"https:\/\/www.1stvision.com\/machine-vision-solutions\/2024\/05\/monochrome-light-better-for-machine-vision-than-white-light.html","title":{"rendered":"Monochrome light better for machine vision than white light"},"content":{"rendered":"\n

Black and white vs. color sensor? Monochrome or polychrome light frequencies? Visible or non-visible frequencies? Machine vision systems builders have a lot of choices – and options!<\/p>\n\n\n\n

Let’s suppose you are working in the visible spectrum<\/a>. You recall the rule of thumb to favor monochrome over color sensors<\/a> when doing measurement applications – for same sized sensors.<\/p>\n\n\n\n

So you’ve got a monochrome sensor that’s responsive in the range 380 – 700 nm. You put a suitable lens <\/a>on your camera matched to the resolution requirements and figure “How easy, I can just use white light!”. You might have sufficient ambient light. Or you need supplemental LED lighting<\/a> and choose white, since your target and sensor appear fine in white light – why overthink it? – you think.<\/p>\n\n\n\n

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Think again – monochrome may be better<\/h2>\n\n\n\n

Polychromatic (white) light is comprised of all the colors of the ROYGBIV visible spectrum – red, orange, yellow, green, blue, indigo, and violet – including all the hues within each of those segments of the visible spectrum. We humans perceive it as simple white light, but glass lenses and CMOS sensor pixels see things a bit differently.<\/p>\n\n\n\n

Chromatic aberration is not your friend<\/h2>\n\n\n\n

Unless you are building prisms intended to separate white light into its constituent color groups, you’d prefer a lens that performs “perfectly” to focus light from the image onto the sensor, without introducing any loss or distortion.<\/p>\n\n\n\n

Lens performance in all its aspects is a worthwhile topic in its own right, but for purposes of this short article, let’s discuss chromatic aberration<\/a>. The key point is that when light passes through a lens, it refracts (bends) differently in correlation with the wavelength. For “coarse” applications it may not be noticeable; but trace amounts of arsenic in one’s coffee might go unnoticed too – inquiring minds want to understand when it starts to matter.<\/p>\n\n\n\n

Take a look at the following two-part illustration and subsequent remarks.<\/p>\n\n\n

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Transverse and longitudinal chromatic aberration – Courtesy Edmund Optics<\/figcaption><\/figure>\n<\/div>\n\n\n

In the illustrations above:<\/p>\n\n\n\n