How interference filters can outperform colored glass filters in automated vision applications

Transcription

1 How interference filters can outperform colored glass filters in automated vision applications High Performance Machine Vision Filters from Chroma

2 It s all about the contrast Vision applications rely on maximizing contrast to enable reliable and robust feature detection. interference filters designed for vision applications can provide greater contrast over a wide range of viewing angles by transmitting the most light that you want and by blocking the most light that you don t want. Chroma Technology offers two types of filters: Standard 40nm-wide filters are intended for routine use while Narrow 20nm-wide filters offer the highest levels of precision. Competitor s Narrow Green Bandpass Filter Standard MV525/40 Green Vision Filter Narrow MV520/20 Narrow Green #1 Vision Filter Color Camera Image Ambient Light + RGB LED Lighting No Filter 49.2% RED/GREEN CONTRAST 18.3% RED/PURPLE CONTRAST 64.7% RED/GREEN CONTRAST 35.1% RED/PURPLE CONTRAST 68.7% RED/GREEN CONTRAST 41.4% RED/PURPLE CONTRAST GOOD CONTRAST BETTER CONTRAST BEST CONTRAST

3 Overview InterferenceFilters Chroma s interference filters provide the best combination of brightness and contrast for machine vision. Chroma Technology s filters for vision applications transmit 95% across the entire passband of the light you want and none of the light you don t want. This combination results in optimal contrast for your imaging. When you also consider the much greater blocking of unwanted light (higher optical density) excellent tolerance of wide viewing angles it s easy to see that filters deliver the imaging performance required for today s demanding vision applications. RED LED LIGHT 630 Red LED Spectral Output Chroma s filters More light where you want it Competitor s filters More light where you don t

4 40nm-wide Standard MV Bandpass Filters plotted with common LED spectra PrecisionFilters Sputtered Interference Filters Durable, sputtered thin films coated on single substrates, no colored glass Best combination of brightness and contrast plus a Lifetime Warranty Better contrast than competitor s colored glassbased filters, which contain toxic heavy metals For routine use, matched to the most common LEDs, always the same wavelengths Greater blocking of unwanted light from laser diodes, LEDs, sunlight or ambient light Excellent tolerance of large viewing angles (AOI) MV380/ nm MV470/ nm MV525/ nm MV585/ nm MV630/ nm MV660/ nm MV785/ nm MV850/ nm See only what you want to see High Performance Machine Vision Filters from Chroma

5 Precision Filters TheSetup To illustrate the performance of Standard 40nm filters, we ll use color discrimination to demonstrate contrast. Everyone s familiar with color, and it s a simple and straightforward way to illustrate differences in contrast, even if your application doesn t involve color. We ll look at contrast at normal viewing angles, wide viewing angles, and how effectively a filter can block unwanted light. Color Camera Image Ambient Light + RGB LED Lighting No Filter No Filter Monochrome Camera Images Ambient Light + RGB LED Lighting MV525/40 Green Vision Filter To help illustrate, we ll use these familiar LEGO bricks as our objects in the following images. LEGO is a trademark of the LEGO Group of companies, which does not sponsor, authorize or endorse this presentation. Poor grayscale contrast Improved grayscale contrast

6 Precision Filters BetterContrast Chroma s filters provide a dramatic improvement in contrast over competitor s colored glass filters. MV525/40 Green Vision Filter = % RED/GREEN CONTRAST 35.1% RED/PURPLE CONTRAST + SAMPLING AREA With Filter Competitor s 532 nm Narrow Green Bandpass Filter = % RED/GREEN CONTRAST 18.3% RED/PURPLE CONTRAST Monochrome camera images acquired with: 1/1.8 sensor and 12mm C-mount lens + ambient overhead light + RGB LED illumination With Competitor s Filter

7 Precision Filters BetterContrast Chroma s filters provide a dramatic improvement in contrast over competitor s colored glass filters. + { } MV525/40 Green Vision Filter Competitor s 532 nm Narrow Green Bandpass Filter The reality is Monochrome camera images acquired with: 1/1.8 sensor and 12mm C-mount lens + ambient overhead light + RGB LED illumination = = Myth #1 Wider is better SAMPLING AREA As a filter s passband widens beyond the bandwidth of the light source, it transmits more and more unwanted ambient light, and less desired light. This diminishes contrast. The goal is to maintain the greatest ratio of wanted to unwanted light % RED/GREEN CONTRAST 35.1% RED/PURPLE CONTRAST With Filter 49.2% RED/GREEN CONTRAST 18.3% RED/PURPLE CONTRAST With Competitor s Filter

8 Precision Filters SuperiorBlocking Sample Area MV525/40 Green Vision Filter Can your filter block unwanted light from a laser or a bright LED? We know that you wouldn t aim a laser pointer directly on your imaging field of view, like in this image. MV525/40 Green Vision Filter Optical Density Wavelength But what if you use a laser or structured illumination in your imaging process, and you want to see it in one channel but not in the other channel? Or what if very bright light from a laser or LED that you don t want to detect is either scattered or reflected into the scene? filters provide the optical density you need to block out that bright, unwanted light and see only what you want to see. Green filter with 650nm red laser pointer COMPETITOR 532 nm Narrow Green Bandpass Filter Sample Area COMPETITOR 532nm Narrow Green Bandpass Filter Optical Density Wavelength 650nm Red Laser

9 Precision Filters SuperiorBlocking Sample Area MV525/40 Green Vision Filter Can your filter block unwanted light from a laser or a bright LED? We know that you wouldn t aim a laser pointer directly on your imaging field of view, like in this image. But what if you use a laser or structured illumination in your imaging process, and you want to see it in one channel but not in the other channel? Or what if very bright light from a laser or LED that you don t want to detect is either scattered or reflected into the scene? filters provide the optical density you need to block out that bright, unwanted light and see only what you want to see. { MV525/40 Green Vision Filter High levels of optical density (OD) are unneeded in filters used in vision applications The reality is It s said that OD4 blocking is unnecessary and adds unneeded costs to filters used in vision COMPETITOR applications. 532 nm Narrow Green Bandpass Filter Green filter with 650nm red laser pointer Myth #2 If very bright, unwanted light sources are present in the imaging scene,they need to be blocked. OD3 is not a high enough level of attenuation. } Sample Area Optical Density COMPETITOR 532nm Narrow Green Bandpass Filter Optical Density Chroma s interference filters are designed with high angle tolerance, so they naturally deliver high OD without extra coating layers or cost. Wavelength Wavelength 650nm Red Laser

10 Precision Filters WideAngleTolerance Chroma s filters demonstrate excellent performance at wide viewing angles. MV630/40 Red Vision Filter IMAGED AT CENTER Filter 49.2% Contrast IMAGED AT EDGE Filter 50.5% Contrast Red & Purple LEGO Bricks COMPETITOR Narrow Light Red Bandpass Filter COMPETITOR Filter 48.7% Contrast COMPETITOR Filter 50.3% Contrast IMAGED WITH Wide angle, 6mm lens on 1/1.8 C-mount sensor 50 vertical angular FOV Basic flat-field correction applied to both monochrome images to correct for non-uniform illumination intensity

11 Precision Filters WideAngleTolerance Chroma s filters demonstrate excellent performance at wide viewing angles. Red & Purple LEGO Bricks { } 25 MV630/40 Red Vision Filter Myth #3 COMPETITOR Narrow Light Red Bandpass Filter IMAGED AT CENTER Filter Interference filters fail at high angles of incidence COMPETITOR Filter 49.2% Contrast % Contrast IMAGED AT EDGE Filter COMPETITOR Filter 50.5% Contrast % Contrast IMAGED WITH Wide angle, 6mm lens on 1/1.8 C-mount sensor 50 vertical angular FOV The reality is Unless you engineer them for it. to be used in imaging situations with wide viewing 48 angles, 139 Chroma Technology has designed filters providing equivalent or better performance to colored glass filters Basic flat-field correction applied to both monochrome images to correct for non-uniform illumination intensity

12 20nm-wide Narrow Bandpass Filters plotted with common LED spectra Highest PrecisionFilters Narrow Band Filters for Machine Vision Narrow filters offer the highest contrast. The tradeoff is brightness and exposure time. If the narrow band filter is centered on the peak of the light source, any difference is minimal. For use with laser diodes OR precisely matched LEDs for the highest possible levels of contrast and discrimination Enable precise, reliable ID of multiple colors Recommended for viewing angles 30 degrees Extremely narrow filters <5nm available for multispectral and agricultural applications Narrow band filters must be closely matched to the light source. MV405/ nm MV450/ nm MV490/ nm MV532/ nm MV590/ nm MV635/ nm MV660/ nm See only what you want to see High Performance Machine Vision Filters from Chroma

13 Highest Precision Filters TheSetup To demonstrate the performance of Narrow 20nm filters, let s make it more challenging by using 8 different colors. We ll see if we can identify these 8 different colors and then test the ability to identify a missing color. This is possible by using 2 filters with reciprocal contrast blue and red to provide the best discrimination and then to combine this data into a lookup table to identify each color. Color Camera Image Ambient Light + RGB LED Lighting No Filter Monochrome Camera Image Ambient Light + RGB LED Lighting No Filter } Insufficient contrast to reliably identify colors without using a filter on the camera lens

14 Highest Precision Filters ColorDiscrimination + ContrastControl Identification of Eight Different Colored Objects Color Lookup Table Color ID derived from unique binary codes based on relative brightness ranks in images from both filters. Very simple for an image processing algorithm to compute from paired ranks and correlations with brightness values. Note the latitude afforded by the multiple allowable entries per color. Color Camera Image Ambient Light + RGB LED No Filter Monochrome Camera Images Ambient Light + RGB LED Ring Light MV450/20 Blue Vision Filter MV635/20 Red Vision Filter 1 RED VISION FILTER (MV635/20) BRIGHTNESS BLUE VISION FILTER (MV450/20) BRIGHTNESS By ranking the brightness of each object from 1-8 in each of the Blue and Red filtered images, we can combine these ranks to create a unique, binary ID. 8

15 Highest Precision Filters ColorDiscrimination + ContrastControl Here we ve changed the purple LEGO brick to a blue brick. By applying the same ranking scheme to the images, we find the presence of 2 blue LEGO bricks. We also identify purple as the missing color because no rank pair corresponds to purple in the Lookup Table. Color Lookup Table RED VISION FILTER (MV635/20) BRIGHTNESS Color Camera Image Monochrome Camera Images Ambient Light + RGB LED Ambient Light + RGB LED Ring Light 1 No Filter MV450/20 Blue Vision Filter MV635/20 Red Vision Filter Additional Blue Brick BLUE VISION FILTER (MV450/20) BRIGHTNESS ! Purple is missing 8

16 The next generation of filters for machine vision & robotic guidance As Vision applications evolve and demand more precision from imaging systems, filters deliver the performance you need. { Standard { Better contrast at common viewing angles Precise contrast enhancement highest Equivalent or better contrast at wide levels of contrast for use with laser diodes viewing angles up to 50 and LEDs Better blocking of unwanted light Separation of closely related colors Narrow Enhanced environmental durability, Multispectral imaging, with custom lifetime warranty narrow band filter design and manufacture Environmentally friendly eliminates Better blocking of unwanted light colored glass which contains heavy metals

17 High Performance Machine Vision Filters from Chroma Published in Bellows Falls, Vermont, US Copyright Chroma Technology Corp 2016 Authored by Jeff Carmichael Technical and Product Marketing Manager, Chroma Technology Chroma filters for machine vision may be purchased online or via phone. For more information, please visit or call