The past
decade, all camera manufacturers have been waging what we photographers call a
“megapixel war”. One week, a brand would release a 10 megapixel camera, the
next week a competitor would release a camera with 15 megapixels. The term
“megapixel”, also revered to as MP, has become somewhat of an sales pitch in
itself. But what is a megapixel and why should you care? Is more megapixels
always better? What are the pros and cons of having more megapixels? In this
blog, I will try to answer these questions.
What are megapixels?
A pixel is
a light sensitive cell that resides on a sensor (figure 1). The amount of MP is
a term for the amount of pixels on a sensor. If a sensor contains one MP, it
holds 1.000.000 pixels! That means that a sensor with 10 MP holds 10 million
pixels.
Figure 1: coloured pixels on a sensor
The amount
of pixels on a digital sensor is comparable to the resolution of a computer
screen. Nowadays, a resolution of 1280x1024
or higher is most common. This means that the computer screen has 1280
pixels aligned horizontally and 1024 pixels vertically. This amounts to
approximately 1.3 megapixels. Digital sensors now have a much higher resolution
than that. For instance, a 20 MP sensor has a resolution of 5184x3456. This
means that it contains 5184 pixels horizontally and 3456 pixels vertically and
a grand total of 20.000.000 pixels! But what are the advantages of having that
many pixels on a sensor? Don’t “they” always say that the amount of MP on the
sensor don’t matter? Let’s see if that is true.
Advantages of high MP camera’s
There are
two major advantages when it comes to having a lot of MP. The first, and
foremost, is the fact that a high amount of
megapixels means more data being collected. This results in more details
in the photograph. Figure 2 depicts this. Keep in mind that every block is one
megapixel, thus contains 1.000.000 pixels.
Figure 2: amount of pixels on a sensor. More pixels
means more details captured.
This effect
is most obvious when taking photographs of a scene with a lot of small details.
For instance, grass in a landscape or cloth during a portrait shoot. When you
look at figure 3, which is the same as figure 2 but with added grass, you will
see what I mean by this. The 8 MP sensor has just 2 vertical MP to capture the
entire height of the grass, while the 48 MP sensor has 6. This simply means
that the 48 MP sensor will capture 3 times as much details in the vertical axis
than the 8 MP. In photography, this is
often called “resolving power”. In other words: will you
see very blade of grass as an individual object, or does it become a green
blur?
Figuur 3:
More datapoints (pixels) means more details
The second
great advantage has to do with printing. More megapixels will allow you to
print your work on bigger formats without the loss of quality. Of course, you
don’t need 20 MP to print photographs of 10x15cm. However, if you want to print
a poster of let’s say 160x240 cm, you will need all the pixels you can get. This
all has to do with something we call PPI, or Pixels Per Inch. The higher the
PPI, the sharper the prints will be.
Now, a rule
of thumb, depending on who you ask, is that the minimum PPI must always be 150.
Using this fact we can set up a formula to calculate the maximum enlargement of
the digital photograph.
The formula
reads:
This means, for a
photograph with a 10 MP resolution (3648x2736 pixels), that the maximum
enlargement is 3648/150 = 24,32 inch, approximately 60 cm in
length. The maximum width then is 2736/150 = 18 inch, approximately 45cm. So the maximum
magnification of a 10MP photograph is approximately 60x45cm. If you want to
print larger than that, you will have to lower the PPI and thus get a less
sharp image. It is kind of hard to find a digital camera with less than 18
megapixels nowadays so, if your are not planning on making prints bigger than
60x45 cm, you don’t really need to worry about high megapixel count. However,
if you are planning on making billboards, wallpaper, life size posters of
yourself (or a foxy model), you might want to consider getting a camera with
more megapixels. For comparison, here is the same size photograph, the left one
is 300 PPI, the right one 50 PPI.
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Figure 4:
PPI comparison
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Disadvantages to high
megapixel count
Of course,
as with everything, there are some disadvantages when it comes to having a lot
of megapixels on your sensor. Perhaps the biggest con is that of image noise.
Image noise is created by pixels that start “leaking” light on the neighbouring
pixels because they are full. This is comparable to an ice cube tray. If you
have 8 (or 12 as in this example) slots in this tray, you can fit in a decent
amount of water in them before the slots start leaking into others.
Figure 5: more pixels on the same surface means smaller
pixels
However,
change the amount of slots to 48, as in figure 2, but keep the sensor size the
same, and the pixels will have to be much smaller. Smaller pixels leak light
faster, thus creating more image noise. If you raise the ISO on you camera, the
pixels will be more sensitive to light and thus be “full” quicker.
Figure 6: image noise at high ISO settings
Of course
this is not a problem when shooting landscapes. That is, if you brought a
tripod as all landscape photographers should, or if you shoot in a studio where
you can cater the light to your needs. It will become a problem for a street- or
wedding photographer that have to up their ISO values indoors or during dusk,
to keep a fast shutter speed. So the amount of megapixels that are useful to
you, depends on what you want to do. High megapixel cameras are more suited for
landscape and studio photographers, while lower MP cameras (creating less
noise) are more suited for street-, wildlife- and wedding photographers.
A second
disadvantage of a high megapixel count is that lens flaws become more obvious.
All lenses contain minor flaws that cause aberration( figure 7), deforming,
vignetting etc.
Figure 7: lens flaw: chromatic aberration
Lenses that
use fluorite glass have less problems with lens flaws but are more expensive.
It is safe to say that all flaws in a lens subtract from overall image quality.
Therefore, if you want to use a camera with a high megapixel count, you should
also buy adequate lenses (read: the more expensive ones).
That being
said, I sometimes see people buy a very expensive camera body. Because the body
is so expensive, they don’t have enough money for proper glass, so they buy a
cheap lens with it. This is a very common mistake. The cheap lens will not make
the most out of the resolution your expensive body will offer. Instead, do the
opposite. Buy a more expensive lens with a less expensive body and your
photographs will contain more detail, more contrast and more colour! Of course,
if you want the best, go for a high megapixel camera (if you shoot studio or landscape) AND get an expensive lens.
One last
disadvantage of a high MP count is the file size. A RAW file made with a 20 MP
camera is approximately 25 MB. If you have a 40 MP camera, it will quickly
shoot up to about 50MB per photograph. This means you need bigger memory cards,
a faster PC and more hard drive space. Also, because of the higher resolution,
you have to spent more time processing the images because you will see every
little flaw in that models skin, every crooked hair, every speck of dust..
So, In
summary:
- - The
amount of megapixels that is USEFUL for you, depends on what you want to shoot
- - High
MP count means more details In your photographs
- - High
MP count means bigger enlargement without loss of quality
- - Less
MP means less image noise at higher ISO values
- - Less
MP means less bothersome lens flaws
- - More
expensive lens on a cheaper body is better than the other way around
So much for
his blog! I hope that you have once again learned something useful. Check out http://photojitsu.nl/blogpost.html for more blogposts and useful stuff
to read about photography. In addition, if you want to follow me and my work,
or just want to drop in to say hello, check out my facebook page www.facebook.com/photojitsu or twitter @photojitsu_nl.
Until next
time!
