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The highest quality images are produced by optimizing many key factors.

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This video series will describe the nature of each image quality factor and explain how they can be measured using Imatest.

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Luminance non-uniformity, also known as light falloff, lens shading, or vignetting, is greatly affected by lens geometry.

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Color non-uniformity or color shading is affected by the chief ray angle of light projected on the sensor,

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and the interaction of pixels with anti-aliasing, infrared, and color filters.

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Full characterization of an imaging system will involve testing using a range of different illuminant spectra, including daylight, fluorescent and incandescent lighting.

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Manufactures can use uniformity measurements to ensure that imaging system components perform as expected, and to calibrate non-uniformity correction for each device.

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Imatest measurements can also be used to detect defects like dead and hot pixels, and blemishes such as particles of dust or smudges.

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Appreciating a beautiful photograph should be dependent on the subject, not artifacts that may be present on the lens or sensor.

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The human visual system is sensitive to medium spatial frequencies. Our eyes are less sensitive to high frequency noise and low-frequency non-uniformity.

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Blemish Detect’s filtering system can be tuned to automatically distinguish defects based on how visible they are to the observer,

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similar to the human eye’s contrast sensitivity function.

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The blemish detect module can record the size, location, and number of blemishes apparent in an image.

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Color and luminance shading will typically be greatest at the most open aperture and shortest focal length.

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These lens properties should be controlled during testing.

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Luminance levels are measured in localized areas of the image and compared to the maximum luminance, found near the center.

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This yields relative illumination values around the field

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Optical center is obtained by identifying the peak luminance location

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If this appears far from the geometric center of the image, it indicates a problem with the lens elements or their alignment.

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Light Falloff can be corrected during post-processing.

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However, vignetting can be considered visually pleasing as it draws focus to the center of the image.

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To measure uniformity, an image of an evenly lit surface needs to fill the entire frame.

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The target should be as uniform as possible.

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This can be achieved with carefully balanced reflective lighting of a surface, or more easily achieved with a high quality light box or integrating sphere.

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Ideally, the lens should be focused to infinity and not the target to measure defects on the lens or sensor.

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For measuring sensor defects, a lens is not needed.

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Dark field tests, in which all incoming light is blocked off from the camera, can also be used to analyze Dark Uniformity, Dark Noise, and Hot Spots.

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Uniformity modules display contour plots depicting regions of various light levels in an image. These plots are available in 2D or 3D.

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Color uniformity profiles are plotted across the vertical, horizontal, and diagonal lines along the image.

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Grid plots show metrics across an array of sectors within the image.

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These measurement breakdowns are the basis of CPIQ and ISO standards.

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To learn more about the appearance and testing process for other key image quality factors, please visit imatest.com/IQFactors.

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For a free 30-day trial, please visit Imatest.com/free-trial.