Quiz 2

Q01Effective Color Illumination

Which do you prefer, gold or silver? In terms of value, your answer will always be gold, but color is a personal preference. Due to similar refl ectiveness gold and silver appear almost the same when converted to grayscale.

When using white lighting

Image through color camera
Image through monochrome camera

Which of the following lighting colors gives the greatest contrast between gold and silver?

  1. Red
  2. Blue
  3. Yellow
  4. Green

Correct answer:B.Blue

When considering gold and silver colors, silver has a high refl ectivity over a wide range of the visible spectrum while the refl ectivity of gold drops off in the blue wavelength (500 nm) and below. Therefore, when blue lighting is used on a silver/gold target, the gold appears darker.

In the images below, you can see gold appears dark under blue lighting, where as there is little difference when using red lighting (image on the right).

Q02Outer Diameter Measurement & Lens Selection

How to go about measuring a 10 mm (0.39") outer diameter on a cylindrical target with a vision system.

Which of the following lenses is generally considered ideal?

  1. A lens with 6-mm (0.24") focal distance
  2. A lens with 25-mm (0.98") focal distance
  3. A telecentric lens

Put (1), (2) and (3) in order of selection priority (most suitable first):

  1. (2)→(1)→(3)
  2. (3)→(2)→(1)
  3. (1)→(2)→(3)

Correct answer:B.(3) → (2) → (1)

When inspecting dimensions using a vision system, lens characteristics can affect the accuracy of an inspection. This question revolves around the differences between three lens types: telecentric, short focal distance and long focal distance. When using a lens that has a short focal distance it typically has a wide angle of view as well. So the size of the captured target will change greatly as the target moves nearer or further from the camera. In other words, when you want to measure dimensions, the variation in measurements will be smaller using a lens with an angle of view closer to 0 degrees. Therefore, when comparing 25-mm (0.98") and 6-mm (0.24") lenses, a 25-mm (0.98") lens with a narrower angle of view is more suitable for the inspection.

A telecentric lens is optically designed so that the angle of view is almost 0 degrees, and is well suited for dimension inspections. Hence a telecentric lens would be the best.

For these reasons, the correct answer isB. (3)Telecentric lens→(2)25-mm (0.98") lens→(1)6-mm (0.24") lens

Q03Minimum Detectable Flaw in a Quality Inspection

One of the main roles of machine vision systems these days is defect inspection for quality control. Due to the high speed image processing capability, machine vision can be used to inspection for fl aws and defects that may occur in the manufacturing process.

However, since high levels of quality control are expected, it is important to know what capabilities the vision system can perform to.

When checking for defects, what is the minimum detectable size of a flaw? Select the appropriate size based on the conditions listed below.

[Conditions] Inspection area: 50 mm × 50 mm (1.97" × 1.97"),Camera used: 1-million-pixel camera with 1000 × 1000 pixels,Minimum detectable size on CCD: 2 pixels

  1. 0.01 mm (0.0004")
  2. 0.1 mm (0.004")
  3. 1 mm (0.04")
Black spot on plastic target / Magnified view of the defect

Correct answer:B.0.1 mm (0.004")

Q04Pre-processing Image Enhancement Filters

Various pre-processing filters are available for manipulating raw camera images. Effective use of pre-processing filters can dramatically stabilize inspections.

Which filter is the best to give the effect described on the images below?

(a)Emphasize the black spot
(b)Remove the vertical lines
  1. (a) Expansion filter, (b) Shrink filter
  2. (a) Shrink filter, (b) Edge-extraction Y filter
  3. (a) Shrink filter, (b) Edge-extraction X filter

Correct answer:B.(a) Shrink filter, (b) Edge-extraction Y filter

(a) Using a shrink fi lter will emphasize the black spot. A shrink fi lter reduces the brighter areas of an image, resulting in an expanded black spot.

Raw image / Image with shrink fi lter As the white area around the black spot contracts, the black spot expands. / Image with expansion fi lter As the white area around the black spot expands, the black spot contracts or disappears.

(b) Using an edge-extraction Y-fi lter, can hide vertical lines. The fi lter emphasizes rows of horizontal contrast in the image, thus removing the vertical lines in an image.

Raw image / Edge-extraction Y-fi lter The horizontal direction is emphasized, and vertical lines disappear. / Edge-extraction X-fi lter The vertical direction is emphasized, and the contrast of vertical lines is enhanced.

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