What exactly do I mean by "Great Image Quality"?

Fuji X-Pro 1 35mm f/1.4

Its often the case that when any of us describe a camera or len's output we talk about the Image Quality or IQ. This however is usually left undefined. I thought it would be useful to write about what I mean by this and open this up for discussion over at Google+ to try and come up with an idea of what this might mean for us, individually and collectively.

SHARPNESS / RESOLUTION / DEFINITION / ACUTANCE

I've put these all together, because these are all words to describe how well defined an image is. Though they all mean slightly different things, we all know the difference between a soft looking file on our screens, where its difficult to pick out particular details when the image is scutinised at high magnification levels and one that draws us in by showing us things we may have been unable to see when we pressed the shutter. 

The number of pixels comes into this, as this affects what we can see. However that is less important to me than the actual apparent sharpness of the image. In general I've had the best results from cameras with no Anti-Aliasing / Low pass filters, such as the Leica M8 and M9,  Sigma SD14 and the Kodak SLR/n and Pro 14n. Of my current cameras the Fuji X-Pro 1 shows the highest levels of perceived sharpness and clarity.

A CLEAN IMAGE

Theres not a lot of point in having all this sharpness if the images have lots of noise and artefacts. Colour noise, luminance noise (grainy look), moire etc. Many of the cameras indicated above, with the absence of the Fuji, have some problems in this area. In terms of the Kodaks, these were pretty widespread. Cameras with strong AA filters tend to have less, but the perception of sharpness is somewhat blunted.

COLOUR REPRODUCTION

Camera sensors vary widely in colour reproduction, and personally I do like good strong colours that are representative of what we see in nature. I have always found "Leica colour" very attractive, though I would never describe it as particularly accurate. The Fuji X-Pro 1 is the only camera I've used that approaches 100% accuracy in how it renders colour. The fact that it does so in a "punchy" way, makes it very attractive to me. 

DECENT HIGH ISO PERFORMANCE

I think we all expect pretty good results up to ISO 1600 these days and something usable at 3200 and 6400. This hasn't always been the case of course, but in the light of whats available, we would probably be disappointed if we didn't get that. In terms of my everyday photography its not often that higher settings than those are required. Again the cameras that exhibit the highest levels of sharpness are often those with the poorest high ISO performance, with the exception of the Fuji X-Pro 1.

DYNAMIC RANGE

Blown highlights and dense shadows that produce noise when lightened are not attractive to look at or desirable. Cameras need to be able to contain a decent amount of detail in both the lightest and darkest parts of the image. The current 16MP sensor from Sony is a good example of this, as is the Fuji X-Pro 1, though this can be a problem without careful raw processing.

THE LENS FACTOR

Obviously the lens we put on our cameras can affect the results, though I always put forward the opinion that this is secondary to sensor performance in determining how my pictures look. Flawed lenses are a problem however, with soft corners, CA and fringing spoiling the overall look of the image. For a camera to have top class image quality I would expect a range of lenses to be available for it that do justice to what the sensor can produce.

RAW AND JPG.

I think we would also like our cameras to produce a decent jpg. Whether we use Raw or not, its obviously useful for the camera to produce a useable straight out of camera file. For me this shouldn't be overprocessed. By this I mean the tendency to pile on the noise reduction and then sharpen up the picture after that. This produces a fairly nasty result, fine for web use and small scale reproduction and printing but often disappointing when compared to raw processing. There are very few cameras that give me what I consider to be a useable jpg. Two of them are made by Fuji. The X-100 and X-Pro 1.

You've probably guessed where I'm going with this. When I first got the Fuji X-Pro 1 I expressed the opinion that it had the best image quality I'd ever seen. That opinion still holds true, and for the reasons above. The sharpest results I've ever seen are still from a Leica M8, closely followed by the M9. I've seen impressive results from a Pentax 645D and Nikon D800E, when having some raw file samples to play with, but overall I've never seen such a wide range of usable images created from one camera until I got the X-Pro 1. 

High resolution cameras, such as full-frame or medium-format can give astonishing results, but this is generally restricted to low ISO's. The Nikon D800 is a mighty beast, but doesn't seem to have the high ISO performance of the Fuji, and like most Nikons the jpgs. from what I've seen, are somewhat "muffled". 

The difference seems to be in the way the X-Pro 1 sensor is designed, and Fuji's claims for it seem justified. I've yet to see any file I've that I have taken with the camera, at any ISO, with any lens that has disappointed me and I cannot remember ever thinking that before.

I'd be very happy to open this up for discussion over at Google+ and if you would like to contribute then the link is below. My interpretation of image quality may be different to yours, and your priorities may be different. Its interesting how IQ is often quoted with no real explanation of what it actually means. This is why I have outlined what it means to me. It would be useful to see what others think about this.

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