How many Pixels/MegaPixels do I need when I buy a digital camera:
This is an issue that I thought about for quite a while before deciding to
buy a digital camera. No one seams to tell you how to compare the quality
of digital pictures to how they will print out or to that of standard 35mm film. Since I am not a
professional photographer, I was mostly concerned about picture resolution and
hoped that the camera would take care of all the other issues for me (color rendition,
noise, tonal range? Who knows what else). After a lot of tinkering
and reading on the web, this is what I learned:
Primarily I want a camera that will look as good as a point and shoot camera
when I look at it on the computer screen, and when I print it off at a reasonable
size. I wrote another section regarding picture size and resolution when
viewing on the screen and printing off. You should probably read that
section before continuing on with this section. I also wrote a
section on the limits of your vision and how that relates to the resolution
required to print clear digital images as well. You should probably read that
section before continuing on with this section as well.
Now that you understand the differences between screen resolution and print
resolution, here is a chart of the various camera resolutions and the type of
images you can create:
Camera
Resolution (Megapixels) |
Typical
Picture Size (pixels) |
Picture
Size on Monitor @ 72dpi Setting (inch) |
Picture
Size on Print (inch) |
175 dpi |
200 dpi |
300 dpi |
0.29 |
600 x 480 |
8.3 x 6.7 |
3.4 x 2.7 |
3.0 x 2.4 |
2.0 x 1.6 |
0.48 |
800 x 600 |
11 x 8.3 |
4.6 x 3.4 |
4.0 x 3.0 |
2.7 x 2.0 |
0.79 |
1024 x 768 |
14 x 11 |
5.9 x 4.4 |
5.1 x 3.8 |
3.4 x 2.6 |
1.00 |
1152 x 864 |
16 x 12 |
6.6 x 4.9 |
5.7 x 4.3 |
3.8 x 2.9 |
1.29 |
1280 x 960 |
18 x 13 |
7.3 x 5.5 |
6.4 x 4.8 |
4.3 x 3.2 |
1.92 |
1600 x 1200 |
22 x 17 |
9.1 x 6.9 |
8.0 x 6.0 |
5.3 x 4.0 |
3.07 |
1920 x 1600 |
27 x 22 |
10.9 x 9.1 |
9.6 x 8.0 |
6.4 x 5.3 |
6.29 |
3072 x 2048 |
42.7 x 28.4 |
17.6 x 11.7 |
15.4 x 10.2 |
10.2 x 6.8 |
You can see that for full screen viewing and printing a 5"x7"
@ 175dpi a 1 MegaPixel camera will be fine. I chose a Sony DCRPC100
digital camcorder that can take 1 Megapixel pictures on a memory stick and video on a miniDV
tape. Here is an example of a 1152x864
@ 72dpi 12"x16" picture that came right off the camera with no
altering. The camera automatically saves the 1152x864 images @ 72 dpi
(12"x16"), so in order to print them out at an acceptable quality you
have to change the picture's defined attributes. I attached a few pictures for you to test out
these changes and the resulting print quality.
Print Test: (Print
Test 1152x864 @ 175dpi 4.9"x6.6", Print
Test 1152x864 @ 108dpi 8"x10.67")
Download the pictures by right clicking on the link and selecting "save
link as" or "save target as". Then print them out using photo editing software.
Both of these images should appear identical on your screen and on your web
browser. This is because I did not change the number of dots in the
picture at all, only how the dimensions were defined, and your screen shows
picture by the total number of dots. For the first picture, I wanted to
get the largest size picture with great print quality. This means that I
have to print out at 175dpi or greater. In order to get 175dpi for good
printing, I had to redefine the picture resolution to 175dpi from its default of
72dpi. This reduces the print size of the picture by (72dpi/175dpi) 41.1%
from what you see on the screen, which results in picture dimensions of
approximately 4.9"x6.6". To check that 175dpi creates
4.9"x6.6" divide the number of dots available in the picture by the
new resolution (864dots/175dpi) 4.937". You will see this 5x7 (4.9"x6.6") prints off clean at 175dpi with no
visible jagged edges. For the second picture, I was determined to create
an 8x10 and live with the resulting print quality, instead of printing the
largest possible size with great print quality. In order to create a
picture that prints out at approximately 8x10, I reduced the size of the picture
by about (8"/12") 66%. In order to maintain the number of dots and not
alter the picture I had to change the resolution of the 8x10 (8"x10.7") to 108dpi. To check the maximum dpi available for
printing at this size, divide the number of dots by the new dimension
(864dots/8") 108dpi. When you print this picture out you can
start to see a few jagged edges on the house's tower edges. This is the
trade-off for making a larger print out. None of the information in these
pictures was changed just the defined dimensions. To check that the
picture information was maintained you can check the total dots in the picture
which should be 1152x864 (4.937"x6.583" @ 175dpi = 864x1152,
8"x10.667" @ 108dpi = 864x1152).
As you can see from these images the unaltered 1 Megapixel camera pictures
hold up well for on screen viewing and printing up to 5x7, and even 8x10 if you
aren't scrutinizing the picture. In reality, I can print higher quality 8x10
pictures by maintaining the 175dpi resolution and changing the dimensions of the
picture to 8"x10.667" and allowing the software to do some thinking
for me. If I allow it to, the photo editing software will fill in
the pixel gaps that are created with "Bi Cubic Interpolation", so
effectively the software figures out what a pixel would would look like between 2
other available pixels, fills in the gaps and reduces the jagged edges.
The resulting picture is (8"x10.667" @ 175dpi =
1400x1867) effectively
creating a 2.6 Megapixel image from your 1 Megapixel camera images.
Although these images aren't quite as good as a true 2.6 Megapixel camera, it
might be good enough for what you are trying to do. This works as long as you don't try to stretch the picture too far, an
11"x17" would definitely not look good.
If you are going to be professional and try to blow up images to 11x17, then you would
need to buy a camera around 6 MegaPixels in order to reproduce the quality and
grain size of 35mm film.
Now that you know how
much resolution you want for good pictures, find out how much that is going to
cost you in number of pictures a camera can hold, disk storage and computer
performance.
If
you didn't read the section on the differences in creating and editing pictures
for screen viewing and printing, you can read that now.
If
you didn't read the section on the limits of your vision (Visual Acuity) and how
that relates to digital images, you can read that now.
If you have any questions please feel free to email me at: johnatblahadotnet.
Check ebay's
"Business Graphics"
section for low cost auctions of imaging software
Check ebay's "Desktop Publishing" section for
low cost auctions of imaging software
Check ebay's
"Digital Camera & Accessories" section for low cost auctions of Digital Cameras & accessories
Links to more information on Digital imaging:
The imaging
resource
ZDnet:
Digital Cameras a beginner's guide
High resolution digital
Image Gallery
How many pixels in
a digital image?
Digital or 35mm
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