Image Quality Factors for Cameras and Lenses

Image quality is one of those concepts that is greater than the sum of its parts. But you can't ignore the parts if your goal is to produce images of the highest quality. Every image quality factor counts.

This page introduces the key image quality factors, describes how Imatest™ measures them, and explains what, if anything, can be done to improve them. It is a guide to Imatest organized by image quality factor. Additional information can be found under Tour (organized by module) and Imatest Documentation.

To illustrate the quality factors, we use this early morning image of Monument Valley from Hunt's Mesa, near the Arizona-Utah border. A 13x19 print (available for purchase) is breathtaking, though it can't capture the experience of grabbing the camera gear and running for the truck as the storm broke. Hunt's Mesa isn't public land; you need a Navajo guide to get there. Tom Phillips does an excellent job.

The image was extensively edited. The unedited image, straight from the RAW converter (with some tonal adjustment) is shown below.

When people ask me about "digital manipulation" I delight in telling them that I would no more manipulate an image than Ansel Adams. Of course I'm jesting. In Ansel Adams: A Biography, Mary Street Alinder describes how Adams printed his famous Moonrise over Hernandez image. He'd spend the entire morning making test prints — dodging, burning, and (chemically) manipulating them until they met his exacting standards. It took him that long even though he kept meticulous notes. Then he'd spend the afternoon making prints. From a processing viewpoint he would have loved digital. But probably not from a business viewpoint. Thanks in part to his brilliant business manager he earned more in an afternoon of printing than most of us earn in a decade.

There are two key aspects of image quality. Factors affected by post-processing. Contrast, color balance, color saturation, etc. These are the factors that can be enhanced in the darkroom — digital or chemical — under the control of you, the photographer. For example, higher contrast images usually score higher in visual quality assessment tests, unless the image is clipped. Because of their great importance to photo finishers these factors are the focus of much image quality literature. But they're outside the scope of Imatest. Factors intrinsic to cameras, lenses, and printers. Sharpness, noise, dynamic range, color accuracy, color gamut, etc. Imatest focuses on these. Imatest modules are summarized on the right.

Summary table

This table summarizes the image quality factors described in detail below.

Quality factor	Chart	Module	Comments
Camera, lens
Color accuracy	GretagMacbeth ColorChecker (24-patch)	Colorcheck, Multicharts
	IT8.7	Multicharts
	ColorChecker SG	Multicharts	Imatest Master only
	Custom "pie" charts	Multicharts	Imatest Master only
Dynamic range, Tonal response, Contrast	Step charts	Stepchart	Transmission charts such as the Stouffer T4110 recommended for DR.  Algorithm
	Reflective step charts	Dynamic Range	More convenient for measuring DR than Stepchart because it doesn't require a transmission chart.
	Special charts: ISO-16067-1, QA-62, EIA Grayscale, ISO-14524 OECF, ISO-15739 Noise	Stepchart	Imatest Master only. Most are available from Applied Image.
	ColorChecker, ColorChecker SG, IT8.7, Step Charts	Multicharts
	SFRplus	SFRplus	Does not measure DR. Highly automated. Measures several factors.
Exposure accuracy	Step chart (reflective)	Stepchart
	GretagMacbeth ColorChecker	Colorcheck
Lateral chromatic aberration	Slanted edge	SFR	Printable by Test Charts
	ISO 12233, Applied Image QA-77		Printed on photographic media
Lens distortion	Square or rectangular grid or checkerboard,	Distortion	Printable by Test Charts or displayed on LDC flat screen monitor with Screen Patterns.
	SFRplus	SFRplus	Highly automated. Measures several factors.
Light falloff, vignetting	plain, uniformly lit surface	Lightfall	Can be displayed on LDC flat screen monitor with Screen Patterns.
Noise	Step charts	Stepchart
	GretagMacbeth ColorChecker	Colorcheck
Sharpness (MTF)	Slanted-edge	SFR	Printable by Test Charts  Algorithm
	ISO 12233, Applied Image QA-77		Printed on photographic media
	SFRplus	SFRplus	Highly automated. Measures several factors.
Veiling glare (lens flare)	Reflective step chart with "black hole"	Stepchart
Color moiré	Log Frequency	Log Frequency
Software artifacts	Log F-Contrast	Log F-Contrast
Data compression	Log F-Contrast	Log F-Contrast	Not yet fully supported
Prints
Dmax (deepest black tone)	Custom test chart printed from file, scanned on profiled flatbed scanner	Print Test	Gamutvision extracts these properties from ICC profiles.
Color gamut