Part 4 – Image Quality

Introduction

OK,
enough about the handling, live view and everything else – what about image
quality?

Well,
I’m going to make things easy this time and start with the conclusion first.
The 40D has excellent image quality. Canon’s innovation when it came the 40D’s
10MP CMOS sensor was not to revolutionise anything in particular, but was to
essentially obtain the same image quality as its predecessor, while adding 2MP
of resolution. Couple this with a better processing engine and you have image
quality which is as good as the market currently has to offer in a non Full
Frame sensor. Luminous Landscape caused quite a buzz when they announced that
the 40D had IQ (Image Quality) that not only rivaled that of the 5D, but
actually surpassed it. As much as I’d love to say that was true, I can conclusively
state that this is not the case. The 5D still has a noticeable edge in the major
aspects of both detail and its level of noise at high ISO’s. However, the 40D
is close. Shown separately, given two similarly shot scenes I’m almost positive
that I (and anyone else) would not be able to tell the difference. Side by
side, and zoomed in, you can see that the larger 5D sensor still holds the
edge. Compared to the 30D, I find the noise levels pretty indistinguishable –
with a slight advantage going to the 40D. The difference is of course that you
get 2 extra megapixels for either minor improvements in printing size or a
greater latitude for cropping.

As
an aside, I actually believe that scientific methods of testing cameras are
becoming less and less useful. Nikon and Canon, the two leading manufacturers,
have had several generations of cameras now to get this whole thing right, and
the fact that the 40D produces excellent image quality at any ISO is absolutely
unsurprising. The thing that makes a
difference is the ability for the camera to provide the necessary flexibility,
glass and tools to provide the photographer with the best chance of capturing
the shot he / she needs. In test, the 40D was able to do that superbly which is
a testament to both its sensor and its handling. Before I prove my case
however, I’ll give a few necessary examples of the 40D’s image quality
performance.

Highlight
priority

When
this feature was announced, I was intrigued as to how it would perform under
real world situations. The promise of a great dynamic range within highlight
areas should be of great interest to a very large number of photographers, as
it’s the area which is the hardest to pull detail back from when you do not
expose correctly (or have no choice but to blow the highlights). The highlight
tone priority feature can be set through the Menu option. When you enable it,
you need to be aware of two things:

1. Canon claims that there will
        be slightly more shadow noise in the image
2. The minimum ISO you can shoot
        at is ISO 200

Because
of item #1, I didn’t make too much use of this feature while I was shooting in
high ISO at ringside. However, when walking around in the bright sunlight of San Gimignano, Italy as I was recently, it felt
like the perfect time to try it out. Below is the same scene shot about 30
seconds apart. The only difference was that the first image had Highlight Tone
priority set, and the second image did not.

The
first image, exposed with Highlight Tone priority on and with EV +2.0 so that the highlights in the
clouds would be blown, came off the camera as follows (direct conversion from
RAW to JPG, no processing):

 

The
second image, without Highlight Tone priority but exposed in identical fashion with the same shutter speed, ISO and
aperture, came off the camera as follows (direct conversion from RAW to JPG, no
processing):

If you look at the images, you can see some minor
differences. But it’s also hard to tell conclusively as so much of the
highlights appear blown in both. So the real test should really be how much of
the information can be pulled back out of the highlights.

This is possible through post processing. For each image, I
performed the following steps:

• Convert the image to 16 bit TIFF
• Open the image in Photoshop
• Apply levels and change the midtones to -0.7 (which
  darkens the entire image)
• Use the burn tool (set to 30%) and apply selective
  editing to the sky area only
• Repeat the burn once more

The result of the first image is as follows:

Processing the tone priority image starts to get
interesting. You can see that a very large amount of colour and detail was able
to be brought back to the image – more than I’d typically expect. The cloud
doesn’t take on that washed out, blotchy look any more but can be for the most
part, individually distinguished.

Doing exactly the same for the second image result in this
image:

For the non tone priority image, this is what I’m more used
to looking at with an image containing blown highlights. You can rescue the
image to a certain extent, bringing back a bit of colour into the sky but you
still have large areas which are total white.

 

I mentioned ISO earlier by the way. I checked both image and
at low ISO, any differences in the noise in the shadow areas between the two
images is imperceptible.

The conclusion? The new Canon sensor and Digic III
processing engine is definitely capturing greater dynamic range in the
highlights than was previously possible. There are some minor drawbacks but
these are considerations rather than major hindrances. Also you have to
consider that for most normal subjects, you won’t be blowing highlights (and
therefore noticing the extra DR one bit). It’s more for specific cases.
Nonetheless, this is an excellent feature and when shooting at ISO 800 and
below, I leave this feature permanently turned on.

 

High ISO performance

High ISO performance is very good. As a Nikon shooter in
2005 and part of 2006, I always used to envy the high ISO performance of the
20D’s (note, the high ISO dominance of Canon is about to be seriously
challenged by the latest Nikon’s, the D300 and D3). The 40D continues in the tradition
of excellent low light performance. High ISO performance is extremely important
in many forms of photography alhtough, it’s not so much for the absence of
noise. Noise is often manageable and can be reduced. Instead, poor high ISO
sensors typical suffer from the a lack of colour and dynamic range as you move
up the ISO range. This is where I’ve really appreciated the CMOS sensors and
the 40D excels in all aspects. As I stated above, the 40D does not have the
same level of high ISO performance as the 5D, but it’s as good as it currently
gets for cropped sensors at the time of this write up. 

I am not going to provide too many examples here as there
are plenty of studio samples from many other sites to study ad infinitum. However,
to give an illustration of real world performance, here’s a snapshot of one my
dogs in my living room. This is on a poorly lit day, taken with the 35mm f/1.4
L lens mounted on the 40D. I’m shooting wide open at f/1.4 (hence the shallow
DOF) and handholding with 1/20s at ISO 1600. Note, I shot this with in camera contrast
and sharpening set to +1 (which I always leave on to save time processing), but
with high ISO reduction turned off. NO post processing has been applied to the
images unless otherwise stated.

The base image first of all (click to enlarge):

 

The focus, as you can probably tell is on the leading eye. Noise
at this resolution is completely unnoticeable as you’d expect from a web
resolution shot from a decent DSLR. 

It’s not until you zoom in 100% on the full 10MP image you
start seeing noticeable noise levels. The following is a 100% crop of the full
image. Remember this is with NR off.

First thing I noticed was the level of detail being captured
which is very good. Here you can still make out the tiny eyelashes in the
reflection of his eye. I hold the camera very steady generally so doubt I’m
losing any detail as a result of hand shake. There is a bit of sharpness drop
off but more likely, this is down to the fact that I’m shooting wide open at
f/1.4. Noise is definitely noticeable but in my opinion very acceptable. 

It can be improved however. This time, I developed the same
image using DPP but with NR turned on. I cropped for the same image but this
time also applied a small unsharp mask to bring back any lost detail. Now we’re
left with this:

Here we see an additional, small amount of detail lost
(although you can still make out individual hairs) but in return get a noticeable
reduction in noise. The level you have to print at before noise gets noticeable
is really large.

Importantly, notice in both cases of the image that dynamic
range and colour are both still very good. Highlights in the reflection of the
eye are retained and the colour on his markings is accurate and pleasant.

The other thing I want to highlight here, and its the reason
for choosing to shoot my dogs, is that their entire fur (as you will have
noticed) is black. Noise shows up in these areas very easily so I consider this
to be worst case (rather than shooting outside in broad daylight at ISO 1600
where any camera looks good).

To vary things up a little, I’ll provide a final couple of
variations of this scene. When trying to get an idea of how the level of noise
appears in we want to make a 4x6” print of the shot. Here, I resized in Photoshop,
for 300 DPI (leaving me with a 1800 x 1200 pixel image). Then I zoomed to 100%
and took a crop which you see below. This is the level of noise you could
expect to see in a print of 4×6.

Here, as you back off a little from the original pixel by
pixel crops that were shown above, you start to get a much better idea that
noise is very manageable in prints. You might see also that the importance of
dynamic retention and quality of colour are really the critical things here as
at even at this print size, problems in these areas would be noticeable.

Just for fun btw, I’ve attached a processed version of the
file. This is how it would typically look before I was posting an image, if I
wanted to do so with this shot. Minor increases in contrast, a little
improvement in reflection, etc. Still, it’s a snapshot, nothing more.

BTW, as an aside, if anyone ever wanted to doubt the quality
of Canon lenses or the EOS system as a whole, bear in mind that the series
above was shot at F/1.4. On another system, where f/2.8 might be your fastest
aperture, to get the same exposure the photographer would have had to shoot at
ISO 6,400 or handheld at around 1/5s! This is just another reason why a camera
can never be effectively judged on its own but only as part of a system.

For experienced users of the 20D, 30D and 5D, none of the
above should be either alarming or surprising. The 40D sensor is an evolution
from Canon, not a revolution. I can safely conclude that adding in adding the
additional 2 MP’s over its predecessors, the 40D has not brought the levels of
noise to an objectionable level. Moreover, it delivers excellent performance at
high ISO’s which are comparable (slightly better) than previous generations,
but not quite as good as, the 5D’s.

Resolution and Detail

OK so if the level of detail in the previous example,
shooting wide open at f/1.4, didn’t impress you, here’s an example to show the
resolving power of the 40D and modern day sensors. Below is an example where
the lens will be almost certainly outresolving the sensor so we get to see what
it’s capable of. Remember, I shoot with in camera contrast and sharpening set
to +1 but other than that, the following images are totally unprocessed. 

First the image itself. This is of the famous Dome in Florence, Italy.
Here I’m shooting in ISO 200 (with highlight priority enabled), 1 / 1600
shutter speed and F/4.6. So I’m stopped down for detail but not that much (click to enlarge).

BTW, before anyone comments on the slightly unusual
composition of including the distracting foreground element (the sliver of
building at the left edge), that was deliberate to allow me to apply lens
corrections in photoshop later.

Anyway, zooming in, we can see a 100% level of detail and
I’ve provided the following three 100% crops.

100% crop #1 (click to enlarge)

100% crop #2 (click to enlarge)

100% crop #3 (click to enlarge)

Now, for me, this is about as good as it gets at per pixel
resolution. If there’s a way to resolve a greater level of detail, it’ll be
meaningless in real world results. In fact, this level of sharpness is actually
way beyond what I’d usually get in real world shoots. I’m usually shooting
portraits, sports / action, etc and the subjects typically move and require
more creative choices of depth of field than f/4.5. This level of sharpness is
actually beyond what I need – if I care this much about per pixel resolution,
then it probably means the subject I’ve captured wasn’t interesting enough to
look at in the first place.

 

Samples

Finally, I’ve included a few samples below which show what
the 40D is capable of in a variety of situations, in the right hands with the
right glass. The fight images are shots I took on set of The Contender Asia of
undercard matches. Note, they do not feature actual contestants of the show.
The travel images were taken when I had a few hours spare in San Gimignano, Italy
recently. All images are after post processing. Click on any image for a larger
version. All images copyright Lawrence Ripsher.