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CONTRASTMAX INTERFERENCE FILTERS FOR AUTOMATED VISION APPLICATIONS.pdf
This document discusses how interference filters from Chroma Technology can provide better contrast than colored glass filters for machine vision applications. It explains that Chroma's ContrastMax interference filters transmit more of the desired light and block more of the unwanted light, resulting in higher contrast images. The document demonstrates through sample images how ContrastMax filters provide clearer discrimination between colors and better performance at wide viewing angles compared to competitor filters. It also dispels several myths about the needs and capabilities of filters for machine vision.
CONTRASTMAX INTERFERENCE FILTERS FOR AUTOMATED VISION APPLICATIONS.pdf
- 1. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision How interference filters can outperform colored glass filters in automated vision applications High Performance Machine Vision Filters from Chroma®
- 2. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision It’s all about the contrast Vision applications rely on maximizing contrast to enable reliable and robust feature detection. ContrastMax 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 ContrastMax filters: Standard 40nm-wide filters are intended for routine use while Narrow 20nm-wide filters offer the highest levels of precision. GOOD CONTRAST Competitor’s Narrow Green Bandpass Filter 49.2% RED/GREEN CONTRAST 18.3% RED/PURPLE CONTRAST Color Camera Image Ambient Light + RGB LED Lighting No Filter BETTER CONTRAST ContrastMax Standard MV525/40 Green Vision Filter 64.7% RED/GREEN CONTRAST 35.1% RED/PURPLE CONTRAST BEST CONTRAST ContrastMax Narrow MV520/20 Narrow Green #1 Vision Filter 68.7% RED/GREEN CONTRAST 41.4% RED/PURPLE CONTRAST
- 3. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision InterferenceFilters Overview Chroma’s ContrastMax interference filters provide the best combination of brightness and contrast for machine vision. 630 Red LED Spectral Output RED LED LIGHT Chroma Technology’s ContrastMax 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 it’s easy to see that ContrastMax filters deliver the imaging performance required for today’s demanding vision applications. ▸ the much greater blocking of unwanted light (higher optical density) ▸ excellent tolerance of wide viewing angles More light where you want it Chroma’s ContrastMax filters More light where you don’t Competitor’s filters
- 4. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision Sputtered Interference Filters PrecisionFilters High Performance Machine Vision Filters from Chroma® 40nm-wide Standard MV Bandpass Filters plotted with common LED spectra MV380/60 350–410nm MV470/40 450–490nm MV525/40 505–545nm MV585/40 565–605nm MV630/40 610–650nm MV660/40 640–680nm MV785/40 765–805nm MV850/40 830–870nm ▸ 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 glass- based 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) See only what you want to see
- 5. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision To illustrate the performance of ContrastMax 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. To help illustrate, we’ll use these familiar LEGO® bricks as our objects in the following images. TheSetup Precision Filters Poor grayscale contrast Improved grayscale contrast Monochrome Camera Images Ambient Light + RGB LED Lighting ContrastMax MV525/40 Green Vision Filter No Filter Color Camera Image Ambient Light + RGB LED Lighting No Filter LEGO® is a trademark of the LEGO Group of companies, which does not sponsor, authorize or endorse this presentation.
- 6. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision BetterContrast Precision Filters Chroma’s ContrastMax filters provide a dramatic improvement in contrast over competitor’s colored glass filters. + ContrastMax MV525/40 Green Vision Filter Competitor’s 532 nm Narrow Green Bandpass Filter = = Monochrome camera images acquired with: 1/1.8” sensor and 12mm C-mount lens + ambient overhead light + RGB LED illumination SAMPLING AREA 165.55 73.83 35.50 150.35 74.11 51.19 With ContrastMax Filter 64.7% RED/GREEN CONTRAST 35.1% RED/PURPLE CONTRAST With Competitor’s Filter 49.2% RED/GREEN CONTRAST 18.3% RED/PURPLE CONTRAST
- 7. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision BetterContrast Precision Filters Chroma’s ContrastMax filters provide a dramatic improvement in contrast over competitor’s colored glass filters. + ContrastMax MV525/40 Green Vision Filter Competitor’s 532 nm Narrow Green Bandpass Filter = = Monochrome camera images acquired with: 1/1.8” sensor and 12mm C-mount lens + ambient overhead light + RGB LED illumination SAMPLING AREA 165.55 73.83 35.50 150.35 74.11 51.19 With ContrastMax Filter 64.7% RED/GREEN CONTRAST 35.1% RED/PURPLE CONTRAST With Competitor’s Filter 49.2% RED/GREEN CONTRAST 18.3% RED/PURPLE CONTRAST The reality is… 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. Myth #1 “Wider is better” { }
- 8. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision Sample Area COMPETITOR 532nm Narrow Green Bandpass Filter Optical Density Wavelength Sample Area ContrastMax MV525/40 Green Vision Filter Optical Density Wavelength SuperiorBlocking Precision Filters Can your filter block unwanted light from a laser or a bright LED? ContrastMax MV525/40 Green Vision Filter COMPETITOR 532 nm Narrow Green Bandpass Filter 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? ContrastMax 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 650nm Red Laser
- 9. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision Sample Area COMPETITOR 532nm Narrow Green Bandpass Filter Optical Density Wavelength Sample Area ContrastMax MV525/40 Green Vision Filter Optical Density Wavelength SuperiorBlocking Precision Filters Can your filter block unwanted light from a laser or a bright LED? ContrastMax MV525/40 Green Vision Filter COMPETITOR 532 nm Narrow Green Bandpass Filter 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? ContrastMax 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 650nm Red Laser It’s said that ≥OD4 blocking is unnecessary and adds unneeded costs to filters used in vision applications. “High levels of optical density (OD) are unneeded in filters used in vision applications” { 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. Chroma’s interference filters are designed with high angle tolerance, so they naturally deliver high OD without extra coating layers or cost. The reality is…
- 10. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision WideAngleTolerance Precision Filters Chroma’s ContrastMax filters demonstrate excellent performance at wide viewing angles. Red & Purple LEGO® Bricks COMPETITOR Narrow Light Red Bandpass Filter Basic flat-field correction applied to both monochrome images to correct for non-uniform illumination intensity ContrastMax MV630/40 Red Vision Filter 25° IMAGED WITH Wide angle, 6mm lens on 1/1.8” C-mount sensor 50° vertical angular FOV IMAGED AT CENTER ContrastMax Filter 49.2% Contrast COMPETITOR Filter 48.7% Contrast 141 48 139 48 IMAGED AT EDGE ContrastMax Filter 50.5% Contrast COMPETITOR Filter 50.3% Contrast 137 45 139 46
- 11. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision WideAngleTolerance Precision Filters Chroma’s ContrastMax filters demonstrate excellent performance at wide viewing angles. Red & Purple LEGO® Bricks COMPETITOR Narrow Light Red Bandpass Filter Basic flat-field correction applied to both monochrome images to correct for non-uniform illumination intensity ContrastMax MV630/40 Red Vision Filter 25° IMAGED WITH Wide angle, 6mm lens on 1/1.8” C-mount sensor 50° vertical angular FOV IMAGED AT CENTER ContrastMax Filter 49.2% Contrast COMPETITOR Filter 48.7% Contrast 141 48 139 48 IMAGED AT EDGE ContrastMax Filter 50.5% Contrast COMPETITOR Filter 50.3% Contrast 137 45 139 46 Unless you engineer them for it. Chroma Technology has designed ContrastMax filters to be used in imaging situations with wide viewing angles, providing equivalent or better performance to colored glass filters. The reality is… Myth #3 “Interference filters fail at high angles of incidence” { }
- 12. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision ContrastMax 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. Narrow band filters must be closely matched to the light source. Narrow Band Filters for Machine Vision PrecisionFilters MV405/20 395–415nm MV450/20 440–460nm MV532/20 522–542nm MV590/20 580–600nm MV635/20 625–645nm MV660/20 650–670nm MV490/20 480–500nm ▸ 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 Highest 20nm-wide Narrow Bandpass Filters plotted with common LED spectra High Performance Machine Vision Filters from Chroma® See only what you want to see
- 13. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision To demonstrate the performance of ContrastMax 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. TheSetup Highest Precision Filters Insufficient contrast to reliably identify colors without using a filter on the camera lens Monochrome Camera Image Ambient Light + RGB LED Lighting No Filter Color Camera Image Ambient Light + RGB LED Lighting No Filter }
- 14. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision ColorDiscrimination + ContrastControl 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. Monochrome Camera Images Ambient Light + RGB LED Ring Light MV450/20 Blue Vision Filter MV635/20 Red Vision Filter 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 RED VISION FILTER (MV635/20) BRIGHTNESS BLUE VISION FILTER (MV450/20) BRIGHTNESS 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 4 2 Identification of Eight Different Colored Objects 7 8 6 1 5 3 7 2 8 3 4 1 5 6 Highest Precision Filters 4 7 2 2 7 8 8 3 6 4 5 1 3 5 1 6
- 15. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 RED VISION FILTER (MV635/20) BRIGHTNESS BLUE VISION FILTER (MV450/20) BRIGHTNESS Color Lookup Table ColorDiscrimination + ContrastControl Monochrome Camera Images Ambient Light + RGB LED Ring Light MV450/20 Blue Vision Filter MV635/20 Red Vision Filter 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. 4 3 7 8 6 2 5 1 5 7 2 8 3 4 1 6 Highest Precision Filters Color Camera Image Ambient Light + RGB LED No Filter Additional Blue Brick ! Purple is missing
- 16. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision The next generation of filters for machine vision & robotic guidance As Vision applications evolve and demand more precision from imaging systems, ContrastMax filters deliver the performance you need. ContrastMax Standard { ▸ Precise contrast enhancement – highest levels of contrast for use with laser diodes and LEDs ▸ Separation of closely related colors ▸ Multispectral imaging, with custom narrow band filter design and manufacture ▸ Better blocking of unwanted light ▸ Better contrast at common viewing angles ▸ Equivalent or better contrast at wide viewing angles up to 50° ▸ Better blocking of unwanted light ▸ Enhanced environmental durability, lifetime warranty ▸ Environmentally friendly – eliminates colored glass which contains heavy metals { ContrastMax Narrow
- 17. CHROMA TECHNOLOGY CORP®www.chroma.com/machine-vision 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 ContrastMax filters for machine vision may be purchased online or via phone. For more information, please e-mail sales@chroma.com, visit www.chroma.com or call 800.824.7662.