worldexpo2007

XXi www.imagexpert.com

Target Design for Automated Inspection of

Toner and Inkjet Print Quality

Yair Kipman ImageXpert, Inc.

Nashua, New Hampshirewww.imagexpert.com


Presentation Outline

• What is print quality?

• Benefits of print quality measurement

• Test target design for automated print quality inspection

• Overview of some important ink and toner features and common measurement approaches

• Examples of manual and automated measurement systems


• Prints Contain... – Text– Halftoned or tinted regions

or images– Line art (charts, sketches,

outlines or diagrams)– Solid areas– Color...

• Print quality is the perceived or measured quality of a printed image

What is Print Quality?


• Is the text sharp?Or are edges blurry or ragged?

• Is the image smooth?Or are there spots? Bands?

Blotches?

• Are the boundaries between different color areas well-defined?Or is there inter-color bleed?

• …

What is Print Quality?


Print Quality Measurement



• Since print quality is what people see, why not just use visual assessment?

– Visual assessment is inconsistent

• it is inherently subjective

• different observers may return different results

• fatigue and changes in energy level can skew opinions

– … it is time-consuming and tedious

– … and qualitative data is hard to use for performance tracking


• Objective print quality analysis is repeatable and objective

– not dependent on operator or inspector

– repeatable over time

• It is quantitative

– numeric results aid tracking, measurement against performance goals

• It can be automated

– automating print quality analysis and data collection saves money and time



Why Measure Print Quality?


• Benchmarking/Competitive Analysis: • Know your competition• Determine desired image quality level• Set quantitative performance goals

• R&D:• Verify performance against goals• Assess changes and improvements• Characterize life tests image quality• Clearly communicate successes and

outstanding issues

• Production:• Analyze performance against goals• Measure consistency by tracking product

quality over time

Print Quality Benefits


Target Design for Automation


• Optical Character Recognition (or barcode) identification for automated test selection, data file labeling and annotation

• Dynamic compensation– Sample position (offset)– Sample size (scaling)– Image brightness (automatic threshold

adjustment)• Networking for data management and SPC

Tools for Automation


OCR for Target Identificationoptical character recognition


Offset

• Scanner cropping files or motion system positions assume consistent target location

• But the sample might be placed differently, or the image might be printed at a slightly different location on the page

• A low resolution image can be used “find” a reference mark on the target, and cropping areas or positions can be adjusted automatically based on the offset between the trained image position and the actual image position

Initial position

Sample position

Offset calculation


Scaling

• Different inkjet printers output the same file with different scales

• Scaling for X and Y might be different

• To enable automation, scaling must be accounted for automatically

• Using fiducials, the scale of the print is assessed by the software and adjustments are made to both the cropping areas and the measurement Regions of Interest (ROIs)


Automatic Threshold Adjustment

• A threshold value indicates to the software what is “dark” and what is “light’

• Threshold values can be calculated automatically from image content (for example: 50% between max peak and min peak) and applied automatically during analysis


Automatic Image Analysis

Once OCR identifies the target type, and scaling and offset are applied, thresholds are calculated and image analysis routines can be applied automatically to different parts of the target

OCR

Offset

Scaling

Image Analysis

Thresholding

Line quality Text quality

Halftone Solid quality

Color


• Data is reported in tab-delimited text files• Data can be exported to other computers on the

network

Networking


Hardware-SpecificTest Target

Considerations


Target Design Considerations

• Scanner-Based Systems:– High resolution scans are

slow

– Vertical (long) scans are slow

• Group high magnification features together for scanning efficiency

• Orient groups of detailed features horizontally to minimize scanning time

• Camera-Based Systems:– Immediate measurement

area limited by field of view of cameras

• Create threshold array small enough to fit in a single field of view of the color camera for efficient threshold calculation

• Design test features to be appropriate sized for measuring with camera

– Each move takes time• Group similar features

together for efficient measurement


Targets and Print Quality Measurements for Toner


Test Targets for Toner

• Targets include both fine details (such as lines and text) and solid areas

• Printing toner targets from PostScript files avoids color contamination from overprinting


Test Targets for Toner

• What is color overprinting? – Here is an example of

yellow being printed in solid cyan lines


Solid Area Quality: Density

Solid area density can vary at different locations on a page

– Measure solid area density in different areas to assess overall quality and variation


Text Quality

Common features for assessing text quality include:

– Character area– Perimeter length– Edge raggedness– Detection of breaks – Detection of fill-ins


Line Quality

Common line quality features include:

• Average line width• Edge raggedness• Edge sharpness• Line area• Line darkness


Resolution

Resolution patterns can indicate how well a system can render detailed image features

Common measurements include:

• Line to space width ratio

• Dynamic range comparison

• Pattern contrast...

Resolution is often measured in both horizontal and vertical orientations since resolution is often directionally dependent


Halftones: Tone Reproduction

Common measurements for halftones include:

• the density or gray value of a series of halftoned patches including highlights and shadows


Background

“Background” is toner that has been developed in the background area well away from printed features

Common measurements include:• Gray average• Area coverage• The number of spots in a

given size range in a given area

• Background via RMSGS method


Area Coverage Targets

Area coverage is often used as a method to help determine end-of-life for cartridge yield testing

– Measure percent area coverage of printed material on page


Toner Adhesion Target

Toner adhesion refers to how well the toner is fixed to the paper

Analysis process is destructive!

There are three common ways of measuring toner adhesion:

– Crease test• measure crease width,

brightness, area

– Abrasion test • measure area before and after

abrading

– Tape pull test• measure tape or area before

and after pull test


Banding and Uniformity Target

Banding can be light or dark, random or periodic, horizontal or vertical

– Measure random banding by band sharpness, size, position and contrast

– Measure periodic banding via FFT, periodicity

– Assess print for single frequencies


Ghosting Target

Ghosting is a light or dark “image” of a feature repeated some set distance from the original feature

• Compare the density or gray value of an area immune to ghosting to the density or gray value of an area prone to ghosting


Color Measurement and Estimation

• True color and density measurement requires color measurement devices

–L*a*b* coordinates

–DeltaE (color differences)

–Color density

• Color (L*a*b*) and black density can be estimated by using other equipment that has been carefully calibrated such as a flat bed scanner or camera.

X-Rite® Spectrodensitometer


Test Target Design and Print Quality Measurements

for Inkjet


Test Target for Inkjet

• This test target includes fine details (such as lines and text) and solid areas

• Printing targets from Excel® avoids (most) color contamination from overprinting


Test Target for Inkjet

• What is color overprinting?

– Here is an example of magenta being printed in a solid yellow patch:

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.


Text Quality

Common features for assessing text quality include:

• Character area• Perimeter length• Edge raggedness• Detection of breaks • Detection of fill-ins


Line Quality

Common line quality features include:

• Average line width• Edge raggedness• Edge sharpness• Line area• Line darkness

Since line quality is dependent on orientation, both vertical and horizontal lines are measured


Inter-Color Bleed

Inter-color bleed is the unintentional intermixing of adjacent colorants

Different color combinations often have different quality levels

Common measurements include comparisons of:

• line width• edge raggedness• edge sharpness


Solid Area Quality

Solid area mottle measurement methods include:

• Simple statistics (standard deviation)

• ISO/IEC 13660 using tiled cells or a “moving ROI”

• Cluster-based analysis

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.


Color Measurement and Estimation

• True color and density measurement requires color measurement devices

• Color (L*a*b*) and black density can be estimated by using carefully calibrated equipment such as a flat-bed scanner or camera

X-Rite® Spectrodensitometer


Special Inkjet Considerations


Quality May Different on Different Paper Grades

OEM ink 3rd party ink

Same printer (Canon), same driver settings...

=

=

Photo glossy

Plain paper


Quality May be Different on Different Paper Brands

Canon printerCanon paper

Canon printerEpson paper

Printed using the same printer, same 3rd party inks, same driver settings… but on different paper brands (same grade, both coated)


Measurement Tools


Measurement Tools

Scanner

Handheld

Motion system

Yourmicroscope

Multi-anglecamera system

Different hardware configurations for different applications.

XXi

All configurations use the same software


Research &Development

Production(QA/QC)

Benchmarking

XXi

Different hardware configurations allow you to use measurement tools in all stages of product development including benchmarking (competitive analysis), R&D and manufacturing.

Measurement Tools


Portable System: ImageXpress

• High-resolution image capture (black and white or color, 1024x768 pixels)

• Compact measurement head and laptop computer enable portability

• Firewire camera technology for increased field of view

• Integrated light source• Powerful ImageXpert

image analysis software

For manual, high-magnification image analysis


• Compact measurement head with wide field of view (approximately 40mm x 30mm) and laptop computer

• Firewire camera technology (1024 x 768 pixels)

• Color or black and white• Integrated light source• Full ImageXpert software

For manual, large field, portable image analysis

Wide Field of View Portable System: iXmax


Scanner-Based System

• Economical image analysis system

• 2400 dpi optical resolution (10.6 microns per pixel)

• Color or gray scans• Accommodates samples up

to A3+ size• ADF for full automation (up

to 100 sheet capacity)• Powerful ImageXpert image

analysis software• L*a*b* estimation via X-Rite

software

Automated and interactive image analysis


Manual Motion System

• Excellent entry level system

• Low volume - high magnification solution

• Manual motion stage• Multiple camera options

(color, black and white or both)

• 3 CCD Color camera, 1024x768 per channel

• Powerful ImageXpert image analysis software

For manual, low-volume, high-magnification image analysis


Full-Motion System

• Ideal for larger volumes• Use in both R&D and

production• Multiple cameras allow

multiple resolutions for image capture

• Fully integrated instrumentation can be added such as an X-Rite for true color measurement and a gloss meter

• ADF and rotation stage available for full automation

• Powerful ImageXpert image analysis software

For automated, high volume high-magnification image analysis


Note on Calibration

For all camera-based systems, our calibration process provides three main benefits:

• Accurately translates pixels into real-world units such as millimeters (using a NIST traceable calibration target)

• Accommodates for any distortions caused by the camera alignment or optics

• Ensures consistency over time and between systems

Calibration is critical to image quality system performance


Upgrade Path

Scanner ormanual motion

Motionsystem

Handheldsystem

All of our hardware configurations usethe same software.


• Objective print quality analysis is repeatable and objective

– independent of operator or inspector

– repeatable over time

• It is quantitative

– numeric results enable tracking, measurement against performance goals

• It can be automated

– automating print quality analysis and data collection saves money and time

Review: Print Quality Benefits


Thank you


[email protected]

603-598-2500

Contact Information:

worldexpo2007

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