Why The New 10 Megapixel DSLRs
Are A Major Step Forward

 
Copyright 2006 Clayton Jones
 
by Clayton Jones
Revised September 4, 2006

An excellent article, "Sensors And Sensibilities", was published by Michael Reichmann on his luminous-landscape.com web site in August, 2006.  It summarizes the technical aspects regarding the size and resolution of digital camera sensors, especially manufacturing and image quality issues.  I recommend reading it because it is the best and most clearly written summary on the subject that I have seen.

After reading the article I was moved to write down some additional thoughts regarding sensors, especially two concepts that I have found to be important, but which are rarely, if ever, mentioned in contemporary writing and forum discussions.  These have to do with how the image format relates to printing resolution and what practical effect this has on print size and quality.  I think these comments will be a helpful extension to Mr. Reichmann's article, especially for someone considering the purchase of a new camera.
 

From Prosumer To DSLR

Consider the case of someone who uses one of the 8mp 2/3 sensor "prosumer" models introduced in 2004 (Canon Pro-1, Nikon 8700, Olympus 8080, KM A2, and Sony 828).  These remain the largest sensor high resolution digicams produced to date and are still widely used and loved for their high quality images.

As good as these cameras are, the limitations of the 2/3 sensor are apparent and many users would like to move up to a larger sensor.   Many of these users have held back from buying a DSLR, but are now seriously considering getting one of the new 10.2mp DSLRs currently coming to market as we approach this fall's Photokina.   Why have they waited until now?

 
The 3:4 Image Ratio
Many photographers have grown to love the 3:4 image ratio used by most digicams and consider it the ideal format.  It is a bit longer than the 4:5 ratio used in the film world by 4x5 and 6x7 cameras, which always seemed a bit too short, and is significantly shorter than the 2:3 ratio used by DSLRs which they consider much too long.  3:4 ratio prints are harmonious to the eye, can be made without having to crop a 3:4 image, and fit handsomely in the standard 8x10, 11x14 and 16x20 frame sizes.

Many prosumer users have wanted to move to a larger sensor but have held back from purchasing a DSLR because of the 2:3 ratio and the difference it makes in composing and cropping, hoping that a camera with a large 3:4 sensor would be made (larger than the four-thirds format).   At this point, however, it doesn't look like that will ever happen, and many are resigned to getting a DSLR if they want a larger sensor (medium format digital being unaffordable).

Speaking of medium format, it is important to note that the digital sensors made for these cameras are using the 645 format, which has the 3:4 ratio.  I find this to be significant, as I think it underscores the popularity of this ratio.  At this time, except for a miniscule number of specialty models, all non-DSLR digital camera sensors are 3:4.  Only the DSLRs use the 2:3 ratio. 

The important point here is that in order to make a 3:4 ratio print from a 2:3 ratio image, 12% of the image must be cropped.  That means a 6mp DSLR image, after cropping, ends up with 5.2mp of actual image to work with.  In order to make a 4:5 ratio print such as an 8x10, 17% must be cropped, which leaves just 4.9mp.
 

Printer Resolution

The Reichmann article mentions 300 ppi print resolution. This is the optimum resolution which produces the highest quality print (related to the level of detail the human eye can resolve).  It just so happens that an 8mp 3:4 image produces an 8.1x10.8 print at 300 ppi.  My favorite print size is what I call a "Portfolio Print", which is a 6x8 image on letter size paper.  At 6x8, the 8mp image is 408 ppi.  This allows for some cropping if needed and still remains at or above the optimum resolution.  It is possible to up-res an image (increase resolution) for larger print sizes, but that has it's own issues which are discussed below.

The point here is that for anyone making high quality prints up to 8x10, 8mp is the minimum acceptable resolution.  Until recently, the only DSLRs under $1500 have had either 6 or 8 mp.  A 6mp 2:3 image becomes 5.2 mp at 3:4 (or 4.9mp at 4:5).  An 8mp DSLR image becomes 7mp at 3:4 (or 6.6mp at 4:5).  Both are a step down in resolution from the 8mp prosumer camera.  However, the new crop of affordable 10.2 mp cameras will be 8.9 mp at 3:4 and 8.5mp at 4:5.  We're finally getting there.

There is another related issue that is important to mention here: there is more to this than numbers of pixels.  As Mr. Reichmann points out, the size of those pixels and how it affects image quality is of major importance.  Here is a real world example.
 

Capturing Detail In The Image

Along with a Canon Pro-1, I have a terrific pocket digicam about the size of a deck of cards.  It makes remarkably good 7mp images with a 1/8 sensor.  At that resolution it is a close match to the Pro-1, as far as numbers go.  It can make the same size prints at similar ppi.  However, there is a difference in quality in those prints.  Both cameras have excellent lenses, but the much smaller pixels simply don't produce as good an image.  It's hard to describe the difference but I would say there is a clarity in fine detail and better tonal gradation.  Suffice it to say that larger pixels produce better image quality in a way that isn't directly related to the number of pixels. 

I did some comparison tests, taking side-by-side pictures with the Pro-1, a 6mp Pentax DS and a full frame 12mp Canon 5d.  The differences among all three, even in 6x8 prints, were obvious.  The comparison between the 6mp DSLR and the Pro-1 was the most interesting because it represented a significant decrease in number of pixels but a significant increase in pixel size.  The quality of the Pentax print was better in some ways, due to the much larger pixels, even though there were fewer of them (5.2 vs 8, a 53% increase). However in certain ways the Pro-1's greater resolution was better in that it captured finer detail, such as individual leaves on distant trees.  This is where the higher resolution becomes important.

The question arises as to whether we can simply up-res the 5.2mp image to 8mp or larger.  The answer is yes, but up-resing an image doesn't increase the quality.  It just makes larger prints possible in terms of avoiding pixellation (visible pixels, jaggies on diagonals, etc).  In the real world this can be done successfully, but only until the image's shortcomings become apparent.  For example, the 8mp image might distinguish individual leaves on a distant tree, where the 5.2mp image contains just small clumps of green.  In a small print this is not noticeable.  But up-res it to an 11x14 print and you suddenly see very nicely rendered, unpixellated, clumps of green.  Up-res the 8mp image and you see leaves. 

The more pixels you have, the finer the details that are resolved.  The larger the pixels you have, the greater the image quality.  Both affect the degree of up-resing that can be done to make larger prints. 
 

How Much Can We Enlarge?

At optimum resolution and 3:4 ratio a 10.2mp DSLR can produce an 8.6x11.5 print.  Making larger prints requires up-resing the image, which degrades the result to some degree.  At what degree it becomes noticeable or unacceptable is another matter.  It's the equivalent of enlarging a negative.  A contact print produces the best quality.  As we begin to enlarge, the quality degrades.  We know we can enlarge quite a lot before it becomes unacceptable, and each photographer has his/her own limit.  The same applies to digital.  Of course we can make beautiful 8x10 and larger prints from a 6mp DSLR.  We do it all the time.  But put it next to the same size print from a 39mp medium format sensor and the difference will be obvious.  I am not suggesting that 6mp DSLRs are unworthy.  I am just trying to clarify the issues so that people can make informed decisions.

The bottom line is that to achieve significantly higher quality images and larger prints than our current camera produces, we need at least higher resolution, and a larger sensor as well if possible.  Moving from the 8mp Pro-1 to a 6mp DSLR might improve the quality of the 6x8 prints in some respects, but would resolve less detail and would restrict the ability to make larger prints.  But the new 10.2mp DSLRs, arriving at affordable prices and producing 8.9mp at 3:4, are an entirely new class of camera.
 

Putting It In Perspective

There is a common response found in many on-line forums whenever the subject of these new 10mp cameras comes up.  It goes something like "I don't know what all the fuss is about, 6mp is all anyone needs.  I can make beautiful 11x14s from my 6mp images.  People are too hung up on megapixels".  There is some truth in this because it is always possible to stretch the limits to some degree, but it really comes down to what quality of print the photographer is willing to accept.  Back in the days of film, some people made 11x14s from 35mm negatives and thought they were fine, while others were satisfied with nothing less than 4x5 and many used 8x10.  To the experienced eye the difference was obvious, even in smaller prints.  Anyone who has seen an 8x10 contact print understands.  The same principles apply in digital photography.  I'm getting very fine 6x8 prints from my Pro-1 because I'm printing at optimum resolution, but if I go much larger the limitations begin to show.  To get high quality larger prints I need more and bigger pixels.

Professional photographers don't spend $30,000 or more on medium format digital equipment just because they like spending money.  I mentioned earlier that at 300ppi an 8x10 print requires 8mp (7.2 to be exact; 8mp allows for some cropping).  At that resolution an 11x14 requires 13.8mp, a 16x20 requires 28.8mp, and a 24x30 requires 64.8mp.  This is why the medium format digital backs are now up to 39 mp, and probably will continue to increase as technology improves.

Note: At the small end of the scale, at 300ppi a 4x6 requires 2.1mp and a 5x7 requires 3.1mp.
 

Conclusion

When choosing a new camera, both sensor size and resolution count, and the difference between the 2:3 and 3:4 image ratios must be taken into consideration.  Higher resolution isn't about taking better pictures.  It's about making better prints.  It is important to understand how pixel size and pixel quantity affect image quality in different ways, and how these affect the degree to which we can up-res an image.  The new 10mp DSLRs are the first affordable models that don't drop below 8mp at 3:4 and 4:5 image ratios.  For photographers who are serious about print quality these cameras are a major improvement.
 

Copyright 2006 Clayton Jones  
All rights reserved.  This article may not be reproduced without express permission of the author

Return to: Home Page | Gallery Entrance | Articles Page