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Megapixels

Posted By On December 30, 2004 @ 8:20 AM In Digital Photography | No Comments

We’ve been getting a lot of questions about megapixels lately. Stuff like, “How many do I need?” and “Will my photos be sharper with more?” and “Will more megapixels improve the quality of my images?”

Well, here’s the scoop!

First, how they are determined -

So, you’ve found a camera that has 5.0 megapixels and you’re wondering exactly how they arrived at that number. Did they just grab it out of the digital ether, or is there some math you’re missin’ out on?

Well, the term “megapixel” simply means 1 million pixels. So, that means a 5 MP camera can capture 5 million pixels at its highest quality setting. The more of these pixels you capture, the larger you can print your image. Stop and re-read that last sentence! It’s the main reason for wanting more megapixels.

Alright then, how many MP are you going to need to print the size photos you want to print? Well, it depends on how large you want to print and at what resolution. Now, stick with me here…

For the most part, photo-quality ink jet printers do well with 200 DPI, although 300 DPI is usually considered “photo quality”. I can almost never tell the difference. I’ve seen “OK” results at lower resolutions than mentioned above, but 200 DPI or better always makes a nice print for me. So, we’ll use that number as the minimum and plug it into the following equation:

In order to print a 4×6 at 200 DPI, you need to take the length and multiply it by the resolution, then do the same with the width. Next multiply those results. Don’t worry, this is much easier than it sounds:

4 (width) x 200 (resolution) = 800

6 (length) x 200 (resolution) = 1200

Those are your minimum width and length pixel counts. To print a 200 DPI photo quality 4×6, you would need an image that was 800 x 1200 pixels. Now, to determine how many MP this is:

800 x 1200 = 960,000 – Round up to 1,000,000.

Not too bad. Now we know a 1 MP camera can make a good 4×6 print at 200 DPI. Now, if you want a 300 DPI print, you’ll find after re-running the numbers you’ll need a 2.1 MP camera to do the same job! Goes up fast, doesn’t it?

Here are some charts to save you some number crunching:

200 DPI:

3×5
0.6 MP
4×6
1 MP
5×7
1.4 MP
8×10
3.2 MP
11×14
6.2 MP

300 DPI:

3×5
1.4 MP
4×6
2.1 MP
5×7
3.2 MP
8×10
7.2 MP
11×14
13.7 MP

Also, keep this in mind:

300 DPI is generally considered photo quality. If you go higher than that, it’s not really going to make any difference once the results are printed.

So, if you only print 4×6 photos, a 2.1 MP camera is all you’ll need (only 1MP if 200 DPI works for you).

Here’s an example to illustrate this. Let’s say you take the same photo with both a 2.1 MP camera and a 8MP camera. Now, you go home and make a 4×6 from each camera. Guess what? You won’t be able to tell the difference. And any differences you could detect are probably due to sensor and lens differences. Heck, it’s possible the 2.1 MP camera would give you better results if it had a better image sensor and lens than the 8MP camera!

You see, megapixels alone don’t determine quality and sharpness. They’re simply a measure of resolution—how many dots make up your image. Picture quality and sharpness are determined by the quality of your sensor and lens.

For instance, you can go out and buy that new 8MP camera. Sure, it’s going to capture high resolution images, but if the lens is of poor quality, all you’ll end up with is high resolution images that are not overly sharp and have no fine detail. If the lens isn’t capturing fine detail, you can bet your sensor won’t either.

In addition to the lens, the sensor must be of good quality. I saw a 6 MP camera where the lenses were good (it was an SLR), but the sensor left a lot to be desired. No matter what steps were taken, we just couldn’t get a high level of detail out of that camera. I’ve seen 2.1 MP cameras that did a much better job.

Your best bet to insure you have a good lens and sensor is to stick with name brand cameras. I like Canon, Nikon, and Olympus myself. You may see an off-brand with the same MP count for a lot less, but it may—probably does—lack in these other areas. Try to find online reviews of the camera if you have any question about it. I like dpreview:

http://www.dpreview.com/ [1]

Anyhow, I hope this helps demystify megapixels for you.

Happy Shooting!

~ Steve


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[1] http://www.dpreview.com/: http://www.dpreview.com/