What is a quantitative measure for "Image Quality"?

[GWestphal]

I see Nikon consistently get better ratings for image quality, but I've never seen an objective measure of it. What is "Image Quality"?

 

[fralexandr]

...
various characteristics make up image quality
characteristics like sharpness, color, contrast, and noise
http://en.wikipedia.org/wiki/Image_quality

examples
http://www.pentaxforums.com/reviews/pentax-k-01-review/image-quality.html
http://www.dpreview.com/reviews/nikond40/17

 

[corkyg]

Those criteria are all factors that should be considered. Unfortunately, when you read what someone else has written in general terms, it is frequently how the imagery looks to the reviewer.

 

[blastingcap]

I see Nikon consistently get better ratings for image quality, but I've never seen an objective measure of it. What is "Image Quality"?

Image quality to me means the ultimate RAW that results from taking a photo, which is the result of interaction between the lens and camera body and user skill. (But we usually hold user skill constant.)

RAWs will vary on things like:

Resolution (ability to capture fine details without smearing)
Contrast and micro contrast
Visible noise/Dynamic range
Color accuracy and accurate white balance
Visible optical aberrations (CA, coma, flare, ghosting, vignetting, distortion, astigmatism, etc.)
Lack of processing artifacts like moire

When used to describe a camera body alone, people often use the term "image quality" as shorthand to mean "potential image quality of the sensor." Potential, because the lens influences image quality as well, and a bad lens will hold back the sensor if the lens isn't sharp enough or has aberrations or whatever. Furthermore, other things will feed into ultimate IQ in other ways, like autofocus accuracy, metering, good enough controls to make it possible for you to take the shot in time, etc. so a good sensor is necessary but insufficient to have good image quality.

 

[Gintaras]

I see Nikon consistently get better ratings for image quality, but I've never seen an objective measure of it. What is "Image Quality"?

Almost same as when your doctor asks you: "how you measure your pain on a scale 0 to 10"....

 

[RobDickinson]

DXO marks overall score is some kind of mystery value cooked up in their own labs.

Also remember its normalised to their print size (8mp).

I look at dynamic range, noise characteristics & tonal range and accuracy over anything else.

 

[Munky]

Usually it means the amount of detail a camera can capture with minimal noise and other artifacts. Instead of comparing ambiguous numbers and ratings, I prefer to compare actual images side by side, and make my own conclusion.

 

[you2]

mtf is the typical quantitative method; the areas it is flaw is that mtf can change based on distance (usually the test is at one distance) also mtf does a poor job of capturing clarity, colour cast and bookeh.

 

[JohnnyRebel]

Dx0 scores will be a good quantitative measure. Most people really want a reliable qualitative measure, but there are so many subjective aspects that it's hard. It helps if you know a reviewer you trust.

JR