When it comes to image quality there is
a big misconception that if you want better quality
you need more megapixels. Unfortunately, (or fortunately, depending on how you look
at it) it isn't that straightforward in this video we're going to find out
what really defines image quality. Thanks to
Squarespace for sponsoring this video use coupon code KARL to get a 10%
discount. Over the years, camera manufacturers have dedicated much of
their efforts to improve the number of megapixels
in their latest models. At the start of the century
both Nikon and Canon were producing DSLRs with just
3 megapixels - a far cry from the 100 megapixel cameras we see today.
This drive has led many to believe that megapixels are
all that matters when it comes to image quality
but to better understand image quality considering the number of megapixels
alone isn't enough. You also need to look at
the size and the type of sensor, understand how
images are formed, how light is focused onto the sensor and
consider the pixel size, to get the full picture. I like to use this graphic when
considering image quality as it defines the key
elements that determine image quality. Sensor size, photo
site size, resolution, lens choice, file type, knowledge, and sensor type.
Camera sensors and image quality: The type and size of the camera sensor
has a large impact on image quality there are two
main types of camera sensors: CCD which is Charged Coupled Device
and CMOS which is Complementary Metal Oxide Semiconductor sensors.
Both of these essentially do the same job, they detect light
and interpolate this information as an image.
While CCD sensors used to be the most commonly used type of sensor,
technological advancements combined with the lower manufacturing costs of CMOS
sensors has changed this. Traditionally CCD
sensors produced higher quality and lower noise images
than CMOS sensors when compared at the same low ISO
but used a lot more power however over the years these differences have
become a lot less marked. Although the type of sensor has less of
an impact on image quality than it used to, sensor size or format is something that does have a significant impact.
The 3 most common camera formats are APS-C
or crop sensor, full frame for 35mm and medium format crop sensor cameras are the smallest of the common
sensor sizes measuring approximately 23.5 by 15.6mm Their smaller size, lighter weight and
lower price tag make them a popular choice amongst those just starting photography and they are commonly used in both
entry-level and mid-level cameras. These sensors are relatively new
in terms of photography back in the days of film crop sensor
cameras didn't actually exist the most common film formats were 35mm, medium format and large format film.
Crop sensor cameras only really came out of necessity for a cheaper
alternative to 35 mm sensors and as technology continues to progress
and the prices of sensors reduce we may even see the disappearance of
these smaller sensors altogether. Full-frame cameras are slightly larger
than crop sensor cameras with sensor sizes of about 36mm
by 24mm. Larger and heavier than crop sensor cameras
they offer better image quality, perform better in low light conditions and allow
for greater depth of field control but at a slightly higher price.
The introduction of mirrorless cameras has also changed the game when it comes
to size variations between crop sensor and full frame cameras because they do
not have a mirror system mirrorless 35mm cameras are now
basically the same physical body size as a crop sensor DSLR
camera. This means you can have a higher quality image but in a smaller more lightweight camera body.
Finally medium format cameras with sensors of around
53.4 by 40mm offer the greatest image quality, as well
as greater resolution of the three, however, this quality does
come at a much higher price which means they are often only used by
professional photographers or those looking for the highest quality.
There are however distinct differences even between
medium format sensors, not all medium format sensors are created equal there are a number of medium format cameras on the market
that don't strictly fit the dimensions of a medium format camera
such as the Leica S system which has a sensor size of 30 by 45mm.
Even medium format cameras from the same manufacturer don't always have the same medium format sensor size.
For example the Hasselblad X1D II sensor measures 43.8 mm by 32.9
compared to the 53.4 by 40 mm sensor of the Hasselblad
H6D-100 this is often down to the amount of megapixels that need to be crammed
into a physical space and will dictate what the acceptable
physical dimensions need to be based on the photosite size.
So why does the physical sensor size have an
impact on image quality? To understand this we need to understand how digital images are
formed. The process of how digital images are formed is covered in our free
introduction to photography course but quite simply an
image is recorded when light passes through a lens
and is recorded by the sensor. That sensor previously used to be
film. Sensors are what allow digital cameras to record images
they're made up of millions of photosites which are what record the
information contained in individual pixels. Sensors record an image when the shutter button is pressed,
this exposes the photosites to the incoming photons,
(light) that is then recorded as an electrical signal on the sensor.
The strength of each of these signals is converted to digital
values that essentially produce the image once the exposure has ended
each photosite, due to a filter placed over the top,
is only able to capture one of three primary colors
red, green or blue. The most common of these filter systems is called a Bayer Array.
This array invented in 1974 by Bruce Bayer,
consists of alternating rows of red, green and green, blue filters
this deliberate decision by Bayer was based on the science of human visual
perception. Human eyes are more sensitive to green
light than red or blue so his Bayer Array comprises of 50% green
filters, 25% red filters and 25%
blue. As each photosite is only able to record
one color, certain color data is lost when initially capturing the image,
so a process called de-mosaicing is required to convert the array of primary colors
into the final photo. This is done using certain mathematical algorithms and it
is these algorithms that result in the different
colour representation of the various camera brands
and is ultimately what dictates why a Hasselblad color rendition
maybe different from Phase One. for example. One of the reasons I shoot
Hasselblad is because I found that their natural
color rendition processing to be the best I've seen from any
digital camera. In addition to Bayer Array filter
systems Fuji created a different more random array called an X-Trans
sensor. This randomized pattern uses a 6x6
random filtration method and is better at reducing interference
patterns associated with moire, especially on smaller sensors, partly
because it doesn't require a low pass filter that the Bayer 2x2 array needs
and whilst theoretically an X-Trans sensor can record more resolution
it does have drawbacks in other areas such as software support
and flare-lit situations. Interestingly Fuji must only consider this sensor
design advantageous on smaller sensors because Fuji still
choose to use the conventional Bayer array filters on their medium format
sensors although it's worth mentioning that Fuji,
Nikon, Phase and Hasselblad all use sensors
designed and manufactured by Sony whilst Canon
still produce their own sensors but as mentioned earlier two camera
brands can use the same sensors but their expertise processing
algorithms and lens design can lead to vastly
different looks of the final output image. Other things
worth mentioning in sensor design is back-illuminated
sensors, where the metal wiring is positioned
below the photodiode substrate meaning an increase in light capturing
ability but this itself has required a few other
technical problems to be overcome. Back-illuminated sensors are commonly
seen in Sony cameras where the first full-frame version was
introduced on the 42 megapixel Sony A7R ii and they are now branded as
Exmor sensors which they claim are twice as sensitive to light as conventional
front-illuminated sensors. Common in all sensors now for the last
10 years is microlens arrays which are
essentially tiny lenses over each photo site that
funnel and direct the light more effectively to the sensor of photosites
this increased light gathering ability meant that photosites could become
smaller but this unfortunately also increases the opportunity for
diffraction to happen earlier when closing the
aperture of the lens down. Images shot at small apertures such as
f-16, f-22 and f-32 will have a reduction in
sharpness and contrast due to diffraction.
This unfortunately can only be overcome by using larger photosites and better
lens design. In my opinion and hopefully, if Sony are
listening, I'd prefer you to ditch the 100
megapixel medium format sensor in favor of around 80 megapixels in a 50
by 40 mm dimension with a photo site size of around
6 micrometers or microns thereby combining the best combination in
resolution and photosite size, for better low light
performance and reducing diffraction and while
you're at it, make it a back-illuminated sensor design
too! Unfortunately though many of the
manufacturers went off on a megapixel quest as a marketing opportunity rather than an image quality quest which is of course what it should have been.
Image quality megapixels vs resolution. Many photographers fall into the trap of believing more megapixels equal better
quality and while more megapixels do technically
equate to higher resolution it does not necessarily mean better
image quality or higher resolution the word resolution
after all is derived from the word resolve
and resolving ability which we will explore further.
Megapixels are made up of millions of pixels,
these pixels contain specific color information that make up the image
often used interchangeably with megapixels the term
resolution does not simply refer to the number of megapixels in an image
more accurately it refers to how clearly the medium can capture and record detail
this is particularly important when it comes to printing images
this can be influenced by factors such as lens
and sensor quality, file type and ISO. Often as important as the number of
pixels is the size of the pixels themselves measured in
microns which is determined by the size of the sensor,
this is because you can only fit a specific number
of pixels in a given area, photosite sizes can range from as small as 1.1
microns in a smaller smartphone sensor to 8.4 microns in other larger formats.
Larger photosites can record much better dynamic range
which gives a better transitional tonal value, greater tonal accuracy and better color accuracy. For example the image quality of a 50 megapixel camera phone
will be far less than that of a 50 megapixel medium format camera
this is because the photosites on the smartphone sensor
will be much smaller than those of the medium format larger sensor
which means that the smartphone sensor's ability to capture and record light is
far less. Think of it this way, a larger
bucket will catch more rain than a smaller
bucket. Calculating megapixels and pixel size. Megapixels can be
calculated by multiplying the dimensions in pixels of a sensor
and dividing that number by one million for example an
image with a resolution of 5472 by 3648 would produce about 20 megapixel
image 5472 times 3648 equals 19 million 961
856. divide that by a thousand and we equal 19.96 or call it 20
megapixels. Individual pixel size can be calculated
by taking the width of the sensor in millimeters
divided by the image width in pixels and multiplying
by a thousand for example camera with 5616
by 3744 pixels and a 36 by 24 mil full frame sensor would have 6.4 micron
pixels this is calculated by 36 divided by
5616 and then multiplying by a thousand equals 6.4 microns. Other factors that
influence image quality. While sensor types and
size megapixel count and pixel size are all
important when it comes to image quality there are other often overlooked factors
such as lens choice file type and the setting combinations used to capture the
image that also have an impact. Depending on which lens you're
using the quality of an image can vary greatly even when using the same camera. An image shot with an older model lens will
result in a lower resolution image than the same image shot with a newer model
lens with better optical design even though the same number of
megapixels will be recorded because it's the same camera the newer
lens design will likely have better contrast, color accuracy and sharpness, resulting in better resolution. One of the most important things to consider when it
comes to lens choice is the actual quality of the lens.
Chromatic aberration is one factor that you should pay particular attention to
a common optical problem in lower quality lenses
that results in color fringing along high contrast
edges. Chromatic aberration is a result of dispersion
when wavelengths of colour are focused at different positions on the focal
plane or in simpler terms when a lens fails to
focus wavelengths of colour to the same point. Regardless of how many
megapixels there are in an image if a lens is poor
quality this will always result in a lower quality image when compared to a
lens that does not result in chromatic aberration or
other optical faults. A second factor to consider
is diffraction which can result in reduced sharpness in
an image this is a result of light rays passing through a small opening such as
the aperture if the opening is too small or if the
photo site is too small it causes the rays to overlap and
interfere with each other this interference means light is added
in some places and reduced in others when the rays of
light hit the sensor they create a pattern known as the
airy disk which basically describes the best
focused spot of light if the focused spots of light are too close
it becomes impossible to resolve the individual patterns
causing a loss of sharpness and image quality
file type jpeg versus raw the file format you choose to shoot in
will have a big impact on how much information can be
stored in an image although both file types contain the
same number of pixels raw images store far more information
within those pixels than jpeg images you could think of it as
hidden data which can be extrapolated from the raw
file to produce better quality images whereas a jpeg
compresses the data and there is less available to process
photographic knowledge another factor that influences
image quality is knowledge only if you understand how
cameras work how to correctly expose an image
where to focus what lenses equipment and setting combinations to use
and how to correctly light images to compensate for
dynamic range will you then be able to create the highest quality
images dynamic range refers to the number of steps between the blackest
blacks and the white as whites in an image each
camera and even the different recording mediums
has its own dynamic range although the ultimate goal is to have
the maximum range of tones in between the black and white values
your camera settings also play a role in image quality particularly the aperture
using small apertures like f22 will enhance the diffraction problem that i
mentioned earlier and will result in small details in the
image to be lost causing a softer looking image
understanding the bigger picture as you can see from the points discussed before
image quality does not just depend on the number of megapixels in an image
even though this perception may be perpetuated by camera manufacturers
please don't be fooled although megapixels play a
role in overall image quality they are not the be-all and end-all
instead try to think of image quality as circular with each of the points
discussed working together to give the final result my camera
sensor and lens choices always take all of these things into consideration
so that i can produce the highest quality images possible
so next time you're trying to determine the expected image quality of a given
camera remember to keep in mind each of the
points discussed here. Well I hope you found that useful, thanks
very much for watching. This video is brought to you by
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