Understanding Imaging By Gary Loosley Director of Applied Engineering (Europe & South Africa)

Gary Loosley Began working for DVT directly in September 2000. Previously employed by DVT’s European master distributor for 10 years, as Senior Engineer responsible for design, build, installation, commissioning and training on turnkey solutions based on the DVT product range. >100 DVT installations experience.

Understanding Imaging. Objectives: To answer the following questions. What is imaging? What makes a good image? What parameters will affect my image? How will they affect my image? What are the pros and cons of making these adjustments? In what type of application should I use these adjustments?

IMAGE: A reproduction of the form of a person or object. What is Imaging? Definitions IMAGE: A reproduction of the form of a person or object. IMAGING: The visual representation of an object, for the purpose of diagnosis or data collection, using any of a variety of usually computerized techniques.

What is Imaging? For DVT, Imaging is all about knowing how to set-up the camera and software to obtain a good enough image for the softsensor tools to be able to reliably detect defects, or inspect objects.

What makes a good image

What makes a good image

What makes a good image

What makes a good image

What makes a good image A good image is not necessarily a good looking picture to you. A good image is one which the DVT system will inspect robustly.

What parameters will affect my image? Light level. Exposure time. Gain level. Focal length of lens. Distance from object. Apperture used on lens. Digitising rate. Imager format. CCD or CMOS imager. FOV balance.

The above are inextricably linked with one another. Exposure v Gain The above are inextricably linked with one another. If you need your image to be lighter you can increase either exposure time, or gain.

Exposure v Gain

Exposure v Gain Hi Exposure, Lo Gain Hi Gain, Lo Exposure

Exposure v Gain. Using high exposure and low gain will reduce the dynamic range of the sensor, resulting in a lo contrast image. Notice the blooming in the image.

Exposure v Gain. Using hi gain and low exposure will give a reasonable dynamic range, but will increase the noise in the image to the point where definition is lost.

Exposure v Gain. However, you may not need a noise free image, or high dynamic range to accomplish your inspection task.

Light level v Aperture. Open aperture, (large hole), small f number. Less light required, but small depth of field.

Light level v Aperture Closed aperture, (small hole), large f number. More light required, but large depth of field.

Focal length v object distance. Longer focal length Shorter focal length. 16mm 4.8mm

Focal length v object distance. Notice the barrel distortion in the 4.8mm image. The bottom row of keys on the keyboard appears to bend towards the middle of the image at the left and right ends. Notice also the aberration or blurring towards the extremities of the image.

Digitizing Rate Under image parameters we have the ability to adjust the time taken for the DVT 530, 540 and 550 systems to digitize the analogue levels on every single pixel in the image. 39 ms, 26 ms, 13 ms

Digitizing Rate By selecting 39 ms, these systems will use one A to D converter to convert all of the pixel charges, row by row, into digital information.

Digitizing Rate By selecting 26 ms, these systems will use two A to D converters, in a flip flop fashion, to convert all of the pixel charges, row by row, into digital information. It is theoretically possible for the converters to operate at slightly different levels, thus causing small differencies in the image.

Digitizing Rate It is potentially possible for this effect to degrade precision measurements. DVT recommends that you use 39 ms digitizing rate for all measurement applications.

This can result in slightly increased noise in the image. Digitizing Rate Using the 13 ms option, the systems will continue to use two A to D converters, but with this option, we do not allow the charges on the CCD to settle for the recommended amount of time. This can result in slightly increased noise in the image.

Digitizing Rate 39mS 13mS

DVT’s cameras have the following format image capture devices. Imager Format. The size of the image capture device is described as the “format”, and are usually measured diagonally across the CCD, or CMOS. DVT’s cameras have the following format image capture devices. 1/4” 1/3” 1/2”

Imager Format It’s important to know the format of the image capture device when you are ordering a lens for your system.

CCD and CMOS CCD = Charge Coupled Device Two different technologies. CCD = Charge Coupled Device CMOS = Complimentary Metal Oxide Semiconductor

CCD and CMOS All DVT Image capture devices are CCD based, with the exception of the 510, and 520 systems, which use CMOS. CMOS devices are cheaper to produce, however, they do not offer the same image quality.

Legend 510 Imaging New Features for the 510 New Automatic Imaging Modes Strobe Lighting is NOT Required Part Indexing is NOT Required Factory Performed Image Calibration Saved with Flash Can also be performed manually

CMOS vs CCD CMOS devices use different scheme for transferring images CMOS devices also have different response curves Net Result: Better contrasted image. pixel CCD Pixel Value CMOS Light Energy

510 Image Examples 510 Image 530 Image

Horizontal Streaking Only exhibited with 13 ms digitization time

Applications for the 510 Anything you would use a 530 Except Reading 1D, 2D, or OCR use Intelligent Scanners for these applications.

Measurement Repeatability Good Better Legend 510 Legend 540 FindCircle Caliper StDev 0.01499 0.06495 0.00796 0.05578 Range 0.06348 0.36231 0.04970 0.26270 * Best: Legend 544: 1280 x 1024 CCD

See if you can read the code! FOV Balance. Field of view balance allows a user to even up the illumination through software. Please open FrameWork, connect to a 540 emulator, and load the FOV00x image sequence. See if you can read the code!