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I see a lot of questions which mention IQ. The only meaning I know outside photography is "intelligence quotient" but obviously IQ has some other meaning here.

IQ is used for example in "Lens with small scratches on the front element - how do they affect IQ?" and "Is there an IQ gain from Canon's 18-135 to 24-105L?"

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And don't forget that "IQ" is also used in reference to photographic prints. –  user17799 Mar 16 '13 at 22:52

4 Answers 4

up vote 9 down vote accepted

IQ or Image Quality encompasses all aspects of how a camera and lens capture a scene.

There are a great number of aspect which comprise image quality and they may be attributed to different parts of the camera or lens:

  • Image noise
  • Dynamic-Range
  • Color-Depth
  • Color-Accuracy
  • Sharpness
  • Resolution
  • Distortion
  • Vignetting
  • Aberrations
  • Flare
  • Etc.

They apply differently to different cameras and some such as color-accuracy only apply to an image processed in-camera rather than a RAW file.

Image quality is a property of the camera and lens at a certain setting. Using a different ISO, shutter-speed, image-parameters (JPEG), aperture or focal-length can result in different image quality from the same camera and lens combination.

Just note that many people confuse the quality of an image with its success. A low quality image can be very successful and vice-versa. Success has much more to do with the photographer's skill, subject and moment than it does with the camera and lens.

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1  
All so nice answers to a question "What is image quality?" and while I only asked "what does IQ mean?" these answers are all worth Accepting. But can accept only one, and (for me) this one line makes it: "... can result in different image quality from the same camera and lens combination." –  Esa Paulasto Mar 17 '13 at 15:18

Image Quality

In the context of discussions regarding photography, IQ is shorthand for Image Quality.

More specifically, when speaking of lenses it usually refers to such aspects as chromatic aberration, vignetting, and geometric distortion. Other aspects, such as acutance or resolution are usually referred to as "Sharpness". (Both of the examples you cited refer to the IQ capability of particular lenses.)

On the Digital Camera side of things, Image Quality refers to such parameters as resolution, noise, dynamic range, and color rendition, especially when the processing is done in-camera.

When speaking of Post Processing, Image Quality refers to the accuracy of converting the data from the camera (especially if saved as a RAW file) into an image that is viewable using a display medium such as a print or a digital monitor or other display device. Factors involved include resolution, resizing and file compression artifacts, noise reduction, dynamic compression, and color accuracy.

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I just added links for some of the terms in the answer. –  Michael Clark Mar 16 '13 at 15:30

IQ stands for "image quality".

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We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

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Can you explain a bit more? What is image quality, and what isn't it? –  mattdm Mar 16 '13 at 15:08
    
This was to simply open up the acronym. Definition of the term "image quality" is a larger subject. I originally tagged this to terminology only, but i'm happy with the broadening of the area too. –  Esa Paulasto Mar 16 '13 at 18:14
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The acronym can be found in a pretty simple google search. This site adds value by explaining in depth. –  mattdm Mar 16 '13 at 19:25
    
Please downvote if you don't like an answer that answers the question exactly. Simple question, simple answer, and even then there's many members of this site that have already answered in depth and they said all that I might have said about it. So why would I repeat what others already said? Besides, I did not ask what is "image quality" but "what does IQ mean". –  Esa Paulasto Mar 18 '13 at 18:46
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I didn't downvote, by the way. It's not wrong, but we can and should do better. See the post notice below these comments. –  mattdm Mar 18 '13 at 18:48

In photography, "IQ" means "Image Quality". I prefer to qualify this is as technical image quality, because often the aspects talked about in this context have little to do with what makes a quality photograph. Good technical image quality is usually part of great photographs, but isn't necessary, and conversely, photographs with great technical IQ can still be entirely void of merit.

So, with that caveat aside, technical image quality is the degree to which an actual image matches a perfect ideal rendering of a given scene. This has four major aspects.

  1. The Lens A good lens is often regarded as the most crucial to image quality. See What characteristics make a good lens good? for an in-depth look at aspects of lens design which are important here.
  2. The Sensor (or Film) Different recording media have different tradeoffs, advantages, and flaws. For example, sensor may have higher (or lower) resolution, dynamic range, and noise control. See What characteristics make a digital sensor good? for more.
  3. The Technique While IQ is usually considered without regard for artistic merit, a generally-correct exposure is usually part of it, as is a lack of blur from camera shake. One might even consider lighting here, although that's getting to the gray edges of the definition (slight pun intended).
  4. The Post-processing (and the Print) Once an image is captured, there's a whole 'nuther level of image quality regarding processing the image properly for rendering. For on-screen display, for example, a highly-compressed JPEG with many artifacts would be considered to have poor IQ; for a print, there are numerous factors like bad rendition of shadows, banding from a misaligned inkjet, or posterization from low-bit-depth colorspace conversion.
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