What is Image Quality?

Discussion in 'Micro 4/3 News and Rumors' started by Amin Sabet, Oct 4, 2011.

  1. Amin Sabet

    Amin Sabet Administrator

    Apr 10, 2009
    Boston, MA (USA)
    Image quality is frequently abbreviated "IQ" in photography forums. What exactly constitutes IQ?

    More and more, people are using IQ as a term synonymous with sensor performance. Some people take it further than that, equating IQ sensor performance tests in a lab without a lens mounted. Everyone from the NY Times' David Pogue to your salesperson at Ritz Camera is referring to IQ this way.

    DPReview is the most popular online review site and photography forum in existence. Here is a statement from their new review of the Sony NEX-5N:
    Without question, the reviewer is referring to sensor performance as "image quality". Is that what IQ is? Sensor performance?

    Rewind a couple of decades. In one hand, I have an Olympus Stylus Epic pocket camera (great camera by the way; still have mine), and in the other, a Leica M6 with the latest 35mm Summicron lens. Both are loaded with the same low-speed film, so in effect, their "sensor" is the same. These cameras therefore have the same IQ. Right?

    Some more questions:
    • My camera - by lack of mirror slap, image stabilization, presence of a soft release, or better ergodynamics - makes it easier to hold steadier and thus use a lower ISO with a static subject. Does that affect IQ?
    • My camera lacks an AA filter and can capture more detail. Does that affect IQ? I just used the same camera to take a picture of a patterned cloth and the subject is dominated by color aliasing due to the absence of that filter. Does that affect IQ?
    • My camera often misfocuses a bit and I try to compensate by using some wide radius sharpening? Any effect on IQ?
    • I want to capture a very narrow angle of view. My system has no available supertelephoto, so I'm just going to crop the heck out of the picture before I print it. Any effect on IQ?
    • Perhaps my camera doesn't shoot RAW or the RAW files aren't supported in anything other than the crappy proprietary software it shipped with. Any effect on IQ?
    • All my greens with a particular camera tend to come out a little bit sallow, and I can't find a good RAW processor or color profile which makes that better. Does that affect IQ?
    • Most of the lenses available for my camera are sharp and yet render bokeh which is very much to my taste with soft falloff and lack of doubled elements. Does that figure into IQ?
    • My only lens is super contrasty. Will that affect IQ?
    • My only lens flares like hell. Any effect on IQ?
    • I use great film, but the lab which develops it for me and scans it is awful. Will that affect IQ?
    • My camera has a great sensor and a crap JPEG engine. I eschew RAW. Any impact on IQ?

    Maybe the answer to all those questions is "No", and IQ is simply a formula based on sensor resolution, sensor dynamic range, sensor signal to noise ratio, and sensor tonal range.

    What does IQ mean to you?*

    Once you've answered that question, here's the next one:

    Is IQ the major determinant of what makes a photo good?

    *We had a discussion about this four years ago at DPReview (of all places) where I did my best to address what IQ means to me: http://forums.dpreview.com/forums/read.asp?forum=1029&message=25545477.
    I left out some things back then, but my overall stance is unchanged. That is to say that in general, for the types of photography I do (people photography with moderate print sizes), the lens is far more important for IQ than is the sensor.
     
    • Like Like x 16
  2. goldenlight

    goldenlight Mu-43 All-Pro

    Jan 30, 2010
    Essex
    John
    Thanks Amin, that's very thought provoking and raises some very pertinent questions. I guess you have pretty much quantified what I've always referred to as the overall "look" of an image.
     
    • Like Like x 2
  3. avidone

    avidone Mu-43 Top Veteran

    520
    Jun 24, 2011
    Rome, Italy
    Maybe "naked" sensor performance is what these guys call "IQ" though I got the feeling here it seems to often be used to refer to a combo of that and in camera image processing... Or sometimes to lenses as well. Still I get the feeling that all this IQ business is focused on ( pun intended) resolution, sharpness, barrel distortion, Chromatic aberration, contrast and colour rendering and the like whereas actual Image Quality to me is much more subjective, having to do with how sensor, lens, and camera interact. Even more subjective, I would say, are the factors introduced by the photographer.

    Also, especially the more I work with old, "imperfect" adapted lenses, the more often I get photos which are far from perfect technically speaking but which give me a good feeling and which I like the look of better than some of the higher "IQ" ones. Similarly, why are people getting these high IQ cameras and then using them with toy plastic lenses, pinholes, etc. and using special effect modes and PP to make them fuzzy and grainy and off- colour and so on? likewise why the sudden Lomography fad? I think lots of us are searching in different ways to make photos with a bit more "soul" for lack of a better word.

    This could turn into a whole big Philosophy of Photography tangent

    Sent from my iPad using Mu-43 App
     
    • Like Like x 3
  4. goldenlight

    goldenlight Mu-43 All-Pro

    Jan 30, 2010
    Essex
    John
    I would also suggest that the camera which will give us the best pictures is the one we find most comfortable and intuitive to handle and which we enjoy using the most. It will certainly allow us to concentrate on the subject and making the image, rather than fussing over the controlls whilst the decisive moment passes by - unrecorded! :biggrin:
     
    • Like Like x 3
  5. kevinparis

    kevinparis Cantankerous Scotsman

    Feb 12, 2010
    Gent, Belgium
    Amin... you know my mantra that QI...quality of Image... beat IQ every time

    IQ as some sort of benchmark....is about as relevant as megahertz or megapixels....

    none of it will allow anyone to take a better picture on its own. It may contribute to the result... but it will never make the result....

    You can have the finest kitchen, with a great stove, the latest in Japanese ceramic knives, the finest ingredients money can buy... but if you can't cook...then its all a waste

    On the other hand the spontaneous barbecue with beer and friends on a sunny sunday afternoon might just satisfy you more than the gourmet meal in a sterile snobbish restaurant

    K

    K

    .
     
    • Like Like x 6
  6. goldenlight

    goldenlight Mu-43 All-Pro

    Jan 30, 2010
    Essex
    John
    That's me - on both counts! Point taken, and very well made! :smile:
     
    • Like Like x 1
  7. avidone

    avidone Mu-43 Top Veteran

    520
    Jun 24, 2011
    Rome, Italy
    Kevin, it sounds like we agree on both photography and food. Unfortunately I am still a better cook than I am photographer.

    The best thing my E-PL1 has done for me is to be at least good enough to tempt me back into actually caring about photography again after decades of indifference. It gets me out there trying things rather than just occasional haphazard holiday documentation.Since I had meanwhile only used the lowliest of P&S or cell phone cameras, I could probably also have got some good results from some €200 compact. But of course all the mu43s are a good bit better than that and it also has given me Legacy Lens GAS to keep me busy and out of trouble.

    Sent from my iPad using Mu-43 App
     
    • Like Like x 1
  8. I figure that when I can cast an eye back over images taken with older model cameras from 3, 4, 5, 6 years ago and still love the output, that the quest for "IQ" is taking cameras and sensors to places that may be technically or mathematically better, but not necessarily visually better.

    I'm currently looking to replace my Canon 500D...with a 450D. Why? Because to my eye the older camera with a few less megapixels has the better "IQ".
     
    • Like Like x 2
  9. Luke

    Luke Mu-43 Hall of Famer

    Jul 30, 2010
    Milwaukee, WI
    Luke
    I think you're probably preaching to the choir to a certain extent since people who buy into the m43 ethos are naturally eschewing the best possible IQ. Whatever your definition of IQ is, we can all agree that m43 are not the TOP of the IQ pile....we would likely all agree that the ratio of size of camera/ IQ is likely the best.

    I certainly see Amin's point, but I also understand the need for metrics to define how a camera body will perform. If there are companies who make and sell cameras whose measurable IQ falls short of the high benchmark, it's their job to explain why that metric shouldn't be the most important one to the camera buyer.
     
    • Like Like x 1
  10. kevinparis

    kevinparis Cantankerous Scotsman

    Feb 12, 2010
    Gent, Belgium
    My cookery and photography skills are probably on par.... I'll never play Carnagie Hall, but I can at times hammer out a good tune.

    Just did a quick count of my top 50 most interesting pics on Flickr... been a member there for close to 5 years....

    28 shots from the E-510

    14 from the E-P1

    4 from a Canon 20D

    2 from Canon G9

    and 1 each from iPhone and Canon Ixus.... a 2 megapixel camera from 2000.... and its still my number 3 picture

    No photos at all from my Canon 5D Mk2... or from the Leica M* I am occasionally allow ed to play with

    IQ.... nice to have ... but not essential

    K
     
    • Like Like x 1
  11. digitalandfilm

    digitalandfilm Mu-43 All-Pro

    Jul 18, 2011
    I look at some shots with the OLY E-420 and 520 w/ the Oly 50mm f2 macro and that SOB was the sharpest lens.. and made up for the limited sensor.

    By the same token, put a kit lens on the E-30 and you got the same results.. sensor made up for lens shortcomings.

    I find that the EP3/G3 with good glass is very formidable.. and gives good IQ.
     
    • Like Like x 1
  12. goldenlight

    goldenlight Mu-43 All-Pro

    Jan 30, 2010
    Essex
    John
    Sometimes it's nice to forget the camera and all its theoretical imperfections, just stick it on auto with maybe an art filter just for fun and snap an everyday subject for the simple joy of appreciating its existance.

    iAUTO_PEN_081_r_s.

    E-PL1 with pinhole art filter and whatever technology Olympus built in. I just pressed the button. :smile:
     
    • Like Like x 8
  13. harrysue

    harrysue Mu-43 Regular

    164
    Mar 12, 2011
    What does IQ mean to me?

    It's the ability of a camera body to capture light from high to low levels of sensitivity, with low noise across most of this range, accurate color reproduction, and high detail.

    Is IQ the major determinant of what makes a photo good?

    Composition and the moment trumps everything. IQ is secondary. Very few landscapes are remembered as classics. Maybe a few Adams shots. It's mostly portrait work and journalism that gets remembered.

    So DPR appoints the NEX-N King of Mirrorless Kameras, what's the big deal? I can accept that.
     
    • Like Like x 2
  14. Amin Sabet

    Amin Sabet Administrator

    Apr 10, 2009
    Boston, MA (USA)
    Some aspects of IQ are subjective, eg lens rendering characteristics. For my uses, I would put MFT at the top of the mirrorless system IQ pile excluding Leica M and on par or better compared with every APS-C DSLR system which I have owned (Canon, Nikon, Pentax, and Olympus). Every prime lens I've owned for MFT has been sharp with pleasing bokeh rendition. My Pana 14/2.5 is as sharp with nicer bokeh than my Pentax 21/3.5. My Pana 20/1.7 is sharper with nicer bokeh than any of my compact Canon 24mm or 28mm primes. My Olympus 45/1.8 has a better combination of sharpness, pleasing bokeh, and resistance to color fringing than any short telephoto I have ever owned for an APS-C DSLR.

    If everyone were saying "sensor IQ" instead of "IQ", I wouldn't have any argument. However, there is much more to IQ than sensor performance. Somewhere along the line, that obvious truth seems to have been lost.
     
    • Like Like x 5
  15. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    IQ as used by photographers is a fuzzy term. It simply refers to a personal opinion and not very meaningful.

    There really not such a thing as IQ. An image is a result of many factors or qualities. Some are quantifiable, some are qualifiable. The aspects we can quantify are still relative, not absolute. To say a lens has a resolving power of a 100 l/mm or a sensor has a dynamic range of 12.4 EV is not actually saying anything beyond those number. It cannot determine if something is "good." That requires context (and a viewer).

    You can have the nicest numbers you like, but if the image does not look good, then what is the point? For example, you can optimize a lens for resolution, but that requires minimizing the contrast. And while high resolution images are good, they lose impact if the detail is too flat. Depending on the image area, I would rather a lens have higher contrast than resolution.

    But you also need to understand systemically what these numbers mean. If your lens resolves 100 l/mm, it only does that under the test conditions. You point your lens to a low contrast target and the resolving power will drop. An image is made up of different resolutions across its area depending on the contrast of the objects in the scene--you cannot separate your lens performance from the object.

    And the system is complex. Everything that you choose (or the cameras chooses) and everything around you will impact the image. Whether than is sensor size, focal length aperture, the way you hold the camera, the light, the atmosphere, the angle of the object, how much coffee you have been drinking, everything.

    For me, I look for a total package in my equipment. There is a certain look I like in my work and I look for systems that can help achieve that. But every system is a compromise, and a compromise for a good reason--you would not want an imaging system with infinite dynamic range, for example. My "job" is to work within those limitation and use them to the best advantage. And I find it is in the limits where we find the magic of photography.
     
    • Like Like x 7
  16. goldenlight

    goldenlight Mu-43 All-Pro

    Jan 30, 2010
    Essex
    John
    That paragraph sums it up very nicely. :smile: You must have a really good word processor to be able to write like that! :rolleyes:
     
    • Like Like x 3
  17. Amin Sabet

    Amin Sabet Administrator

    Apr 10, 2009
    Boston, MA (USA)
    Naturally some people will look at my post and regard me as a Micro 4/3 fanboy reacting to an NEX review. Some who know me better know that I have plunked down hard-earned cash on lots of Canons, Nikons, Pentaxes, Olympuses, Sonys, Ricohs, Fujis, Casios, Sigmas... you name it. I also happen to own a new Sony NEX site and am excited about the potential of that system.

    I have no problem with the idea of using a system that has lower image quality than another system. That is besides the point which I am trying to make here. The fact is that sensor performance is not the same thing as image quality. In many cases, sensor performance isn't even a major determinant of image quality. Yet the terms are used interchangeably everywhere we look.
     
    • Like Like x 1
  18. Luke

    Luke Mu-43 Hall of Famer

    Jul 30, 2010
    Milwaukee, WI
    Luke
    I'm quite sure that I see eye to eye with you Amin. The tests that are done and graphs that are compiled are, by and large, a measure of a camera body (although obviously a lens needs to be attached to perform these tests). Or maybe more specificly, its' sensor and processing engine. Unfortunately where m43 kicks the NEX system to the curb is in the "unmeasurables" category. Bigger selection of BETTER lenses...better ergonomy, better (for me) tactile controls, etc, etc, etc.

    I still believe that what they are calling IQ is actually IQ. But I would add a caveat that the IQ is ONLY the measurement of what the sensor (or body) is capable of and all of that is controlled by EVERYTHING else that a camera body (and LENSES.....don't forget the lenses) does to affect the final image quality.

    I've seen great lenses on lesser cameras and toy lenses on great cameras and either set-up can create powerful images. But there must be a way to quantifiably compare different cameras. And if people are so foolish to ONLY use those metrics, then they will have to live with those results.

    But you are absolutely right that the letters IQ to many connote total camera IQ when really it is just sensor IQ. People are being deceived.
     
    • Like Like x 1
  19. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    You sometimes get the feeling "photography" is about buying the NEXt camera...

    I have some cameras and they really take nice pictures. They do exactly what I need them to do. So why would I even be looking for a replacement? I don't buy a new car every three years and I am still on my first wife.
     
    • Like Like x 1
  20. KVG

    KVG Banned User

    May 10, 2011
    yyc(Calgary, AB)
    Kelly Gibbons
    One thing I really enjoy about this forum is people constantly exploring old and new lenses to see the character it gives the images. IQ is just a confusing term to me as so many thing can effect it. I don't use a tripod, use iso 16000, or pixel peep so many of the standard measurements don't apply to me. My camera feels good in my hands, hell give me a crappy old lens and I can still explore and enjoy photography.

    6070072778_851c85c68b_z.
     
    • Like Like x 2