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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®


It’s all about the contrastVision 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’sNarrow Green Bandpass Filter

49.2%RED/GREENCONTRAST

18.3%RED/PURPLE CONTRAST

Color Camera Image

Ambient Light + RGB LED Lighting

No Filter

BETTER CONTRAST

ContrastMax StandardMV525/40 Green Vision Filter



BEST CONTRAST

ContrastMax NarrowMV520/20 Narrow Green #1 Vision Filter




InterferenceFiltersOverview

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


Sputtered Interference Filters

PrecisionFilters


40nm-wide Standard MV Bandpass Filters plotted with common LED spectra

MV380/60350–410nm

MV470/40450–490nm

MV525/40505–545nm

MV585/40565–605nm

MV630/40610–650nm

MV660/40640–680nm

MV785/40765–805nm

MV850/40830–870nm

▸ Durable, sputtered thin films coated onsingle 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


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.

TheSetupPrecision Filters

Poor grayscale contrast Improved grayscale contrast

Monochrome Camera Images


ContrastMaxMV525/40 Green Vision FilterNo Filter

Color Camera Image


No Filter

LEGO® is a trademark of the LEGO Group of companies, which does not sponsor, authorize or endorse this presentation.


BetterContrastPrecision Filters

Chroma’s ContrastMax filters provide a dramatic improvement in contrast over competitor’s colored glass filters.

+

ContrastMaxMV525/40 Green Vision Filter

Competitor’s532 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


With Competitor’s Filter




BetterContrastPrecision Filters

Chroma’s ContrastMax filters provide a dramatic improvement in contrast over competitor’s colored glass filters.

+


Competitor’s532 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



With Competitor’s Filter



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”{ }


Sample Area

COMPETITOR 532nm Narrow Green Bandpass Filter

Optica

l Densi

ty

Wavelength

Sample Area

ContrastMax MV525/40 Green Vision Filter

Optica

l Densi

ty

Wavelength

SuperiorBlockingPrecision Filters

Can your filter block unwanted light from a laser or a bright LED?


COMPETITOR532 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


Sample Area

COMPETITOR 532nm Narrow Green Bandpass Filter

Optica

l Densi

ty

Wavelength

Sample Area

ContrastMax MV525/40 Green Vision Filter

Optica

l Densi

ty

Wavelength

SuperiorBlockingPrecision Filters

Can your filter block unwanted light from a laser or a bright LED?


COMPETITOR532 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…


WideAngleTolerancePrecision Filters

Chroma’s ContrastMax filters demonstrate excellent performance at wide viewing angles.

Red & Purple LEGO® Bricks

COMPETITORNarrow Light Red Bandpass Filter

Basic flat-field correction applied to both monochrome images to correct for non-uniform illumination intensity

ContrastMaxMV630/40 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


WideAngleTolerancePrecision Filters

Chroma’s ContrastMax filters demonstrate excellent performance at wide viewing angles.

Red & Purple LEGO® Bricks

COMPETITORNarrow Light Red Bandpass Filter

Basic flat-field correction applied to both monochrome images to correct for non-uniform illumination intensity

ContrastMaxMV630/40 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”{ }


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

MV405/20395–415nm

MV450/20440–460nm

MV532/20522–542nm

MV590/20580–600nm

MV635/20625–645nm

MV660/20650–670nm

MV490/20480–500nm

▸ 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

Highest20nm-wide Narrow Bandpass Filters plotted with common LED spectra

High Performance Machine Vision Filters from Chroma®See only what you want to see


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.

TheSetupHighest Precision Filters

Insufficient contrast

to reliably identify

colors without using

a filter on the

camera lens

Monochrome Camera Image


No Filter

Color Camera Image


No Filter

}


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.


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

BL

UE

V

ISIO

N F

ILT

ER

(M

V450

/20)

BR

IGH

TN

ES

S

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


1 2 3 4 5 6 7 8

1

2

3

4

5

6

7

8

RED VISION FILTER (MV635/20) BRIGHTNESS

BL

UE

V

ISIO

N F

ILT

ER

(M

V450

/20)

BR

IGH

TN

ES

S

Color Lookup Table

ColorDiscrimination + ContrastControl


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


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



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 [email protected],

visit www.chroma.com or call 800.824.7662.

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