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.

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.