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Issue #0624/1 - Which gives better value for money? Pixel Count or Optical Zoom?

Developments in the digital camera market over the last year have brought into sharp focus some of the irrational decisions made by consumers when making their purchases.

These affect the printer market as well but, prior to considering that aspect next week, this week we take a look at digital camera technology and the situation with primary camera specifications.

Consumers are demonstrating a tendency to buy cameras with the highest pixel count possible while ignoring features such as zoom factor. This article asks the question above and attempts to demonstrate that consumers may be making the wrong decision.

Over the past few years since the introduction of digital cameras to the mass market, the resolution of the sensors used has increased dramatically with pixel counts typically now running to 8MP (upper echelon of consumer market).

Each year, new models push the envelope further and eager buyers snap up the latest models.

However, around a year ago, manufacturers were able to enhance the 5MP models by adding a 5x optical zoom in place of a 3x zoom – a very good move. The development did require the camera to sacrifice its viewfinder but, in doing so, also permitted a much larger display screen to be installed. This meant that the camera became much more usable as an away-from-the-eye device (very much a matter of personal preference and not to everyone’s taste).

Within a year, these cameras were being replaced by models reverting to a 3x zoom lens but pushing pixel count up to 8MP!

Why?

Consumers were not interested in the 5x zoom and were opting for the higher pixel count instead of the higher zoom factor.

In addition, the market for ultra-zoom cameras (Single Lens Reflex style cameras with zoom lenses upwards of 6x) has been falling apart. Sales are much lower than expected, and dwindling; models are being withdrawn; and Konica Minolta has withdrawn from the photography market, passing much of its digital camera assets to Sony.

Why?

Similar story - consumers are opting for small, compact cameras with high pixel counts and foregoing the opportunity of a high-power zoom lens.

Clearly there is every justification for the existence of small, compact, high resolution cameras. Even professionals will often carry around a compact camera for those moments when an off-the-cuff photo opportunity arises.

So, the purpose of this article is to find out what pixel count and lens zoom factor do to image quality and to demonstrate that, unless there are specific reasons for buying the smallest model available, the buyer will always benefit more from a high-power zoom than from a high pixel count.

Then, this sets the scene for a similar investigation of printer specifications next week.

Firstly, we must ask the questions:

• what are pixels?
• why does a high pixel count improve image quality?
• what is the effect of a zoom lens?

Then we can ask the question:

• which is better?

What are pixels?

Pixels are literally the building blocks of a digital image. They are square and, because they are the smallest component of an image, they can only be one colour at any one time.

An image sensor comprises a number of these building blocks, or pixels, joined together in a grid pattern.

For instance, a chess board has eight squares across and eight squares down in a square grid. This makes a total of 64 squares. For the purposes of this article, these squares can be considered to represent pixels (Figure 1).

Where cameras are concerned, the grid pattern is generally in a 4:3 format. So, if we extend the 8×8 grid to 12×9, or 12 pixels by 9 pixels (4:3), we have a sensor comprising 108 pixels – or 108 points of colour with which to create an image (Figure 2).

Either the size of the sensor can be increased in proportion to the number of pixels desired (Figure 3) or it is necessary to see how many pixels it is possible to cram into the same space – i.e. increasing the pixel density (Figure 4). Because changing the size of an image sensor used in a digital camera requires a total redesign of the product, affecting many of its components and incurring a major cost overhead, manufacturers may prefer to keep the sensor sizes fairly consistent, making use of increased pixel density for as long as possible.

What this means is that, if the number of pixels is increased, the pixels themselves must become smaller (Figure 5).

Early digital cameras had sensors that were around the 1MP resolution. This means that 1 million pixels were contained on the sensor, typically measuring about 5mm or 6mm diagonally.

As resolution has increased to 5MP and 8MP, typical sensor sizes in compact digital cameras have also pushed upwards and are now in the range of 8mm to 9.5mm. So we can see that both higher pixel densities and larger sensors offer opportunities for increased image resolution.

Further up the camera scale, many higher-end ultra-zoom cameras, used by photo-enthusiasts, are based on sensors as large as 11mm diagonal. Further up the scale again, digital SLRs of 6MP and above use sensors measuring upwards of 27mm.

Why does a high pixel count improve image quality?

Put simply, the higher the pixel count, the more information that is available with which to create a fine image (comparison between Figures 2 to 5).

Imagine gathering data from a sample of 108 people for a survey into buying habits. The scope for accurate analysis is much reduced over taking a sample from 972 people. Now consider the difference in accuracy between a sample of one million people (1MP) and eight million people (8MP)!

Clearly the higher the ‘resolution’, the higher the accuracy and the better the picture of buying habits.

When we translate that analogy into the reality of the digital camera, we are literally painting a better picture of the subject because we have more points of reference to work with.

What is the effect of a zoom lens?

Now lets consider why a zoom lens is a valuable thing to have.

Any camera has to have an optical system of lenses to allow the device to focus the image onto the sensor. A single fixed lens can, in theory, fulfil that function – remember, as a child, focussing the sun to set light to a piece of paper? However, cameras offer much better image quality and dimensional accuracy by using a group of lenses.

But, create a group of lenses that can not only be moved as a block along the focal plane, but can be moved in relation to one another and it is possible to change the size of the image that falls on the sensor as well as focussing it.

In terms of the effect on the image, this quite literally allows the photographer to get ‘closer’ to the subject.

Thinking back to our survey analogy, this is the equivalent of spending more time with each survey participant. Imagine the additional understanding that could be acquired by spending a day with each participant instead of collecting data just from a five-minute survey!

Which is better?

Now consider which scenario would provide a better understanding of buying habits – a five-minute survey of eight million people or one day spent with each of one million people!

By getting up close and personal, it is possible to get right into the cracks of the subject, seeing and understanding what is hidden from the cursory glance. It quite literally zooms each and every data point individually to provide more detailed information, ignoring all the irrelevant information around the side.

Certainly acquiring more data points gives a finer grained view of the required picture but to get in close allows magnitudes more detail to be gathered of a specific area of interest rather than the general scene.

Let’s see this principle in action. I took four digital cameras ranging from 3MP to 8MP and took identical photographs on each at the widest angle each lens would permit and at the maximum zoom of each lens.

	Sensor Dimensions	Sensor Resolution	Zoom factor
Camera 1	2048 x 1536	3MP	3x
Camera 2	2592 x 1952	5MP	3x
Camera 3	3296 x 2480	8MP	3x
Camera 4	2608 x 1952	5MP	8x

Three of the cameras (at 3, 5 and 8MP) had a 3x zoom, while the fourth camera had an 8x zoom with a 5MP sensor.

So what we need to do is to imagine that we want to create a 30×20 poster print of a portion of the image.

Figures 10 to 13 show what happens when each image is further cropped and enlarged to simulate a large print size – see remarks against each image for further comment. Then, against each image, we’ve taken the enlargement factor right up to detailed pixel level to demonstrate how much more information is gathered by the high-powered lens in comparison to the standard 3x zoom lenses, even when a higher pixel count is involved.

	Figure 10.	At 3MP, the window section is created from just 6 pixels, with the window sub-divider consuming a whole pixel - so, in reality, the width of the section is closer to five pixels. All detail is lost. It is only possible to discern what elements of the image are brick, stone, frame and glass through our knowledge of the subject matter from the other images shown. In the maximum-enlargement image, the jumble of pixels make no sense at all - out of context, they could be anything.
	Figure 11.	Boosted to 5MP, differentiation between brick, stone, frame and glass become a little sharper but, even here, we’re only talking about the window section being defined by seven pixels! Overall, the image rendering is smoother and more pleasing (probably mostly due to better image processing and data compression in the camera) but, in terms of pixel definition, the difference is small. Most importantly though, no detail in the brickwork, stonework or shutters is yet forthcoming.
	Figure 12.	By the time we reach 8MP, we are seeing a clear difference in image quality from the 3MP image, with all outlines showing outlines that are smoother and better defined - but definitely not a huge improvement over the 5MP image. If we try hard, we can imagine that we can see some of the detail in the brickwork but this is rather tenuous. With a window section still only around nine pixels wide, we certainly cannot claim that there is a vast improvement in image definition.
	Figure 13.	Finally, observe the magnitudes of difference in the image created by the ultra-zoom camera based on a 5MP sensor but using the full 8x zoom facility. With 16 pixels across the window section, the effective resolution is double that of the 3MP camera with 3x zoom and nearly double that of the 8MP camera. The image is sharp; detail is visible in the brick and stonework; and additional roofing details and blemishes in the wall are visible - as are the horizontal shutter slats.

We have talked extensively of sensors and pixel counts – but what of the sensors themselves? How far can improvements be taken?

Without attempting to get technical about the different types of sensors, suffice it to say that there are limitations to each. The two most common sensors are the CMOS (Complimentary Metal-Oxide Semiconductor) and CCD (Charge-Coupled Device).

Sensors used in mass market, consumer digital cameras are CCD sensors, where it is said that the limitation is likely to be a resolution of around 10MP.

There is one additional comment that should be made regarding the use of CCD sensors against CMOS sensors. CMOS sensors can typically be manufactured to twice the pixel density – meaning that the same sensor size can offer 12MP from a CMOS sensor against 6MP with a CCD.

In both instances, the sensor size is significantly smaller than a 35mm negative, though CMOS sensors for digital SLRs can be full size in comparison to the imaging area of 35mm film.

There may be ways around this limitation of the CCD sensor so that resolutions can continue to increase, such as increasing the form factor (size) of the sensor. Or, there may be new sensor technologies waiting to burst onto the market or perhaps CMOS technologies could be developed for the consumer market to bring professional quality sensors to the mass market.

Of one thing there is no doubt - one way or another, manufacturers will find ways to continue to increase the numeric specifications of mass market cameras without increasing the cost of the camera.

But, what of the casual, snapshot photographer? Do the technical improvements really increase the value proposition? When prints are made, will they really offer a higher satisfaction level? I have 2MP prints that are every bit as pleasing as 8MP prints!

Surely the value to the consumer can now be increased most effectively by improving the camera elements around the sensor rather than simply striving to increase the sensor resolution. The imaging feature sets available in the latest 8MP cameras certainly leave the 2MP cameras of six years ago standing.

Yet, where zoom lenses are concerned, although the industry has fought hard to move forwards, with zoom lenses up to 12x in some ultra-zoom cameras, the effort has passed largely unappreciated to the point where ultra-zoom cameras have become a threatened breed.

What seems most bizarre about the buying decisions being made a year ago was that 6MP cameras with 3x lens were being chosen against 5MP cameras with 5x zoom lens. This is a very small relative increase in the pixel count, and therefore the quantity of information gathered (a 10% linear increase in pixels across the image), in comparison to a 66% increase in the photographer’s ability to ‘get close’ (think of that football match!) and to make large, high quality prints.

To please the buying public, one way of keeping the fixation with specification rising would be to provide the capability for the camera to interpolate additional resolution (split every pixel so that the number of output pixels is increased) in the same way that interpolation was used to provide a higher pixel count, and therefore higher perceived image quality, on scanners a number of years ago.

In some respects, I’m surprised that interpolation has not yet been used in digital cameras – after all, 8MP could perhaps be turned into an interpolated 16MP, 24MP or 32MP. That, surely, would catch the imagination of specification-obsessed camera consumers? For me – I’d prefer a 12x zoom lens.

~End~

This entry was posted on Friday, August 25th, 2006 at 12:03 am and is filed under Financials, Issues. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.