mega pixels

Great Question. Without going into all of the details, the short answer is the higher the megapixels, the higher the resolution of your picture. Think of it in terms of how a High Definition (HD) Television has a higher resolution than an analog TV. The larger the picture, the more obvious the differences in image quality. Depending upon how good your eye is, you might not notice any difference in a smaller picture. You probably will if you try displaying a 2 Megapixel and a 5 Megpixel full screen on your monitor or TV. Try it out! If you don't notice the difference or don't care, it's not worth it to you to buy a higher megapixel camera.

Dr Baluja,
As Ron said, megapixels are a measure of resolution. And like most technology metrics, in general bigger is better. But as is also true of technology, the vendors don't tend to tell you what level of a given measure is enough.

The word pixel is tech talk for "picture element", or in short, a dot. In black and white photography (called grayscale in digital tech talk) that dot may be any of 256 shades of grey. Since the digital world speaks in binary math instead of decimal math it only uses the digits 0 and 1 instead of 0 to 9. So a greyscale pixel takes 8 bits (which equals one byte). 2 to the 8th power is 256, so those 8 bits can represent the 256 different levels of lightness from black at 0 and white at 256.

Now if you take the same concept and use 3 bytes, that is 3 sets of 8 bits, and apply each set of 8 to each of the three primary colors you can represent 256 levels of each primary color. When added together, you have 24 bits. Again, since we're in binary math, we have 2 digits, 0 and 1, and 2 raised to the 24th power is 16,777,216. Thats where this reference to 16 million colors comes in. And it's true, if you use 24 bits to represent the color of one pixel, that pixel can be any of those 16 million colors!

So now we know what one pixel is.

Resolution, we said, is a measure of the quality of a picture. A digital picture is a series of rows of pixels laid out in a rectangular array. So resolution really is a specification of how many pixels make up each row and how many rows there are that make up the rectangular array of dots that make up the picture.

My camera, for instance, an Olympus 3040Z, has a maximum picture size of 2048 x 1536. That is each row has 2,048 pixels or dots (each capable of being set to any of those 16 million colors), and 1,536 rows. So if you multiply those two numbers together, you get 2048 x 1536 = 3,145,727. Or, rounded off, 3.1 million pixels. Mega stands for million, so my camera is a 3.1 megapixel camera. If you multiply the largest horizontal and vertical specifications for the pictures your camera can take, you will get the megapixel specification for your camera.

Why do we care? The more pixels there are, the more the eye sees the image as a smooth blending of colors from one region to another, say in the subtly varying shades of blue in a sky, and the more smoothly a line looks, say the edge of a one region contrasting with another, like a line of a face against a contrasting background. More pixels mean less jaggy edges.

But at some point, beyond which the eye can discern the difference between pixels, more pixels don't make sense.

Where a very high resolution camera DOES make sense is when you want to zoom in on a small region of a given exposure. If I use all 3.1 million pixels (that is the entire 2048 x 1536 pixels) to make a 4 inch by 6 inch print, I get a beautiful print with no resolution problems my eye can see. (I'll have to crop some of the rows because those ratios aren't the same. If I use the entire 2048 width for 6 inches, then only 1365 pixel rows are need vertically to make up 4 inches of height.)

However, if within that 4 x 6 inch print, I see that it's a wide shot and I'd like to zoom in on my granddaughter who only occupies a small part of the center of the image, I can select a subset rectangle of the pixels, still in the 4x6 proportion, and make a 4x6 inch print of just that small section of the exposure. Now, I'm using considerably fewer pixels, and if I choose an area too small, when blown up to 4x6, I'll begin to see the different pixels and the jagginess of the edges. The picture will not look smooth to the eye, and therefore less acceptable.

If I had your 5 megapixel camera, that same small subsection would still likely have enough pixels in it to render a clear, smooth (unpixelated) image and I'd be very happy with the zoomed in picture.

So beyond a certain megapixel size, more are not valueable for a full image photo, but are valuable for zooming in and using a small part of an original for what is effectively a blow up of just that part.

Rick