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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
Picture Size on Print
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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