Thank you for your Question.
This is one of those situations where the "right" answer is much more
of a "it depends" answer than a simple "yes" or "no".
For your specific situation, and for how you use your digital photos
(ie. viewing them on-screen, and printing them at no larger than 5x7),
you are mostly right.
The opinions of the 'pros' you spoke with are also mostly right, but
again with a large "it depends" attached to them.
Megapixels are a convenient way for marketing types to try to give
consumers an 'easy' way to compare products from different
manufacturers. However, just as with tires and their traction ratings
(where each manufacturer uses a different test to determine the
ratings for their own tires), there's a lot more that needs to be
considered than just the number of pixels in the cameras' sensors.
Whenever you look at the number of pixels, you also need to consider
the size and quality of each of those pixels! Having a lot of small
pixels in a small sensor is usually worse than having less, but
larger, pixels in a larger sensor, since the ultimate purpose of the
sensor is to capture light and convert it into a digital
representation. The larger pixels on the larger sensor will be able to
capture more light, and more accurately convert it into a set of
values corresponding to its color and brightness. The larger size also
helps improve the signal-to-noise ratio, reducing the amount of noise
in the raw captured image, and hence the amount of post-processing
that the camera needs to do to compensate for the noise.
Articles that explains all this in much greater detail can be found here:
Part 1 - http://www.thetechlounge.com/article/121/
Part 2 - http://www.thetechlounge.com/article/123/
Part 3 - http://www.thetechlounge.com/article/134/
The "Beyond Megapixels" article also goes into the many other
parameters that truly differentiate one camera from another, including
the size and quality of the lenses, the quality of the cameras'
control systems for focus, metering, and aperture, and of course the
post-processing and compression of the image into a digital file
format. Remember that the JPEG file format is a lossy-compression file
format, meaning that details are lost even as the file is created by
the camera after the image is captured.
Coming back to the opinions of the pros, it is possible to make their
opinions "right", by saying what they depend on...
Opinion 1: "a 10 megapixel image downsampled to 3 megapixels will look
substantially better than the same image taken originally at 3
It depends... on whether we are talking about two images taken with
the exact same camera that has a 10 megapixel sensor in it. If we are,
then in order for the camera to save the image as a 3 megapixel image,
it needs to post-process the raw (10 MP) image. The scaling will
result in loss of details, and the amount lost depends on the scaling
and filtering algorithm used by the camera's processing system. This
is referred to as interpolation loss. While interpolation loss is
usually more perceivable when scaling up rather than down, it still
happens. After all, if you start out with, say, a 3x3 matrix of values
and you need to reduce it down to a single value, there's many
different ways to go about it and the end result will not be as good
as the original. Now, if you took that original 10 MP image, and
scaled it down on a computer where you may have access to
more-sophisticated interpolation algorithms, then the end result will
indeed look better.
However, if we are talking about images taken with two separate
cameras, then all bets are off. The 'look' of the image will be more
greatly affected by the size and quality of the lens, the size of the
sensor, and the rest of the camera features, than by the mere
difference in megapixels. It used to be the rule of thumb that only
the higher-end cameras (digital SLRs) had the higher megapixel count
due to their larger sensor size; however, with recent improvements in
sensor manufacturing techniques allowing sensor makers to pack more
and more pixels into smaller and smaller sensors, this rule of thumb
no longer holds true. Having just recently shopped for a new digital
camera myself, I can attest first-hand that a high megapixel camera
with a bad lenses, will be a lot worse than a lower megapixel camera
with a quality lenses.
Opinion 2: "an image displayed on a monitor will show all the original
detail even though downsampling occurs"
It depends... well actually, this one is more wrong than right. The
typical computer user runs their computer screen at resolutions that
result in about 72 to 96 dpi. If the monitor is a CRT-type, then each
pixel is actually the end result of physical interpolation of the
nearest 'dots' on the screen. If the monitor is an LCD, then it's more
likely that there's a one-to-one mapping of pixels to the screen,
unless the LCD is having the software-interpolate a smaller screen
size up to fill the full panel size, or software-interpolate down a
larger screen size to reduce it to fit the actual panel size. In any
case, since even a 3MP image will be larger than the typical computer
screen resolution, already the image will need to be scaled down in
order to fit onto the screen, so the quality of the downscaling
algorithm used will ultimately determine what details end up making it
to the screen. Now, if this opinion were coupled with Opinion 1, then
technically yes, a 10 MP image taken with a 10 MP camera, when
compared to a 3 MP image taken with that exact same camera, may have
richer details that survive all of the software-interpolation and
physical interpolation, and those details may be perceivable to the
Opinion 3: "high definition of an image taken with a large format
camera will "jump right out at you" even when displayed as a small
image on a web page."
It depends... on whether that camera has a high-quality lens and a
larger sensor to go along with the megapixel count. If it does, then
there is a good chance it will capture deeper colours, better
gradients, and better focus than a 'cheaper' camera, and that all of
that will survive the downscaling to the small image on a web page.
However, if that high megapixel camera has a compact sensor trapped in
a compact camera body behind a distorted lens, then the image will
still, well, suck.
Since photography is all about capturing light and recording as much
information as possible about that light, bigger is indeed better when
all else is equal. Rarely is all else equal, though! That is why every
reputable digital camera reviewer out there, uses techniques similar
to what you did before you formed your own opinion. They take pictures
of a known subject, then visually compare the results to see what
their own eyes tell them. Then, they factor in how the images will
most likely be used, before stating their recommendations. They know
that a digital SLR, for example, will more likely be used by someone
who is more 'into' photography than a simple point-and-shoot camera
would be, so they hold the dSLR to a higher standard than the simple
point-and-shoot. In your case, since you know that you will be using
the images primarily for on-screen viewing and smaller-format
printing, the only real value to you in taking your photos at a higher
resolution than 3 MP, is to allow you the opportunity to crop your
images down to 3 MP in the comfort of your own home, rather than
trying to frame that perfect shot in the middle of the action.
Ultimately, though, never forget that it's about capturing the right
light, and that the optical features of your camera (such as a zoom
lens) are there to help you capture more of the light you want. Any
post-processing features of your camera (including digital zoom) and
your photo-editing software, are only there to help you get the most
out of the light that you managed to capture.
I hope that this helps Answer your Question. Please let me know if you
would like me to clarify this Answer, by using the Request Answer
Clarification button. Also, please note that there are currently some
issues with the e-mail notification feature of this service, so it may
take me a day or two to find out about your request and to provide the
clarification you seek.
Good luck with your hobby!
Google Answers Researcher