What are "megapixels"?

Let’s start with the megapixels, which are the basic way to measure how sharp your pictures can be. A Pixel (a word derived from “PIX" (short for "pictures") and "ELement”) is the smallest area of a picture with a distinctive color, kinda like a “molecule” of a picture. If you look real close at a TV or at your monitor (especially if it’s an LCD display), you’ll see there are many tiny squares of color making up the image. Each one of those is a pixel. A megapixel is a million pixels. Your computer screen can probably display one MP or so – in other words, if you display a 4-MP image on your computer, there is some detail you just won’t see. A TV image has between one quarter and one half of a megapixel – it gets fuzzy quite fast if you look at it from very close.

So you can have a real good idea of what it means to have more or fewer pixels, check out these three pictures. The images below have 330 thousand pixels (a third of a megapixel), 80 thousand, and 20 thousand. You can see what a low pixel count looks like, when a low-pixel image is shown way larger than it should be. (But remember, you'll never see pixels that big. Even the third-of-a-megapixel image looks fine, so you can KNOW that no image made by a multi-megapixel modern digital camera will ever look as bad as the second and third pictures below).

330,000 pixels ( 1/3 of a megapixel)

82,000 pixels

20,000 pixels

A high MegaPixel count comes in handy when you want to crop pictures, and when you want to make enlargements. For uncropped 4x6 prints, 2 megapixels are usually enough, but for 5x7s and 8x6s, you kinda need to go up to 3 if you want a sharp picture. If your picture will be looked at from a small distance, I’d suggest a 4MP minimum for pictures that will be enlarged to 8x10. Then again, if your picture will NOT be inspected closely (say it is on a wall behind a couch, so no one will get closer to it than a meter or so away), then 8x6s of 2MP images, or even 8x10s if your 2MP camera has a really sharp lens, should be all right, and 8x10s of 3MP images are also definitely all right if no one comes to within 3 feet or so of them. I have a ton of 8x6s on my wall behind my bed. Most are 2MP, a couple are 4MP, and one is a really sharp 1MP (as far as 1MP images go).

I insist that, unless you're making posters, you don't need more than 3 megapixels, maybe 4. Two-megapixel images make fine 8x6s, and don't let the folks at the store tell you otherwise. Below are a bunch of pictures, all taken with two-megapixel cameras. Do they not look sharp? When you click on these thumbnails to open each file, it might look just a tad grainy, but that's because you're blowing them up to the size of a monitor, about 12 inches on a side, and then looking at them from very close. Besides, your monitor can't show detail as dense and fine as a print could .This means these pictures would make fine 8x12s if you're not scrutinizing the 8x12 prints from like a foot away, or looking at then on your computer. And the 4x6 prints made from these pictures are very, very sharp indeed. I don't think anyone needs much sharper pictures than this, unless you're making calendars, having stuff printed on magazines, or trying to sell your photographs. (Pictures taken by 4-megapixel SLRs are used professionally, like on calendars and ads, though, so you REALLY don't need more than 4).



I hope these pictures keep you from blowing a fortune on a super-high-resolution camera. THIS IS A VERY IMPORTANT POINT: Don't buy more megapixels than you need, and don't let the camera companies' marketing departments tell you how much you'll need. Three or four megapixels is all you need, even for 8x12s and for some cropping if you're gonna get 4x6s. Sure, 5MP images might be sharper, but unless you print them out huge, or crop a lot, you never even really get to see all that detail. So if you're thinking about a 5-to-8 MP camera, consider getting a 3 or 4 MP camera instead, one with a sharp lens and a not-too-noisy sensor, or a smaller camera, or one with a bigger screen, etc.

As I mention a few times on this page: How sharp the lens is, and how grainy the sensor is, can affect image quality even more than resolution. So there's much more to it than megapixels. As you can see in the "Don't buy more megapixels than you need" section, a camera with more megapixels can sometimes deliver lower image quality!!! (You can click here to go straight to the comparisons that show this.)





























 

Basics

A digital camera is really not that diferent from a film camera. On a film camera, light is focused by a lens onto a rectangular piece of film. Because different areas of the film are exposed to different colors and brightnesses, different areas undergo different chemical reactions, and so an image is recorded. Once the lens is focused, and the shutter is opened a certain width through a certain amount of time, the shutter is then closed again and the film is moved out of the way to be replaced by a fresh unused one. How much the shutter is open and for how long, along with how much light is outside and how sensitive the film is to it, determines how dark or bright the picture will be.

On a digital camera, light is focused by a lens onto a rectangular CCD sensor. Because different areas of the sensor are exposed to different colors and brightnesses, different areas undergo different ionization processes, and so an image is recorded. Once the lens is focused, and the shutter is opened a certain width through a certain amount of time, the electrical charges induced in the different areas of the sensor by the focused light are "flushed" to a processor that converts them into an image file and then saves that file on a memory card, or in the camera's small internal memory. How much the shutter is open and for how long, along with how much light is outside and how sensitive the sensor is to it, determines how dark or bright the image will be - but you can see how bright the image will be before you take it by looking at the electronic screen on the back of the camera, which is connected to the CCD sensor to show you the "predicted" image in real time. You can also have this screen show you an image file after the picture is taken, so you can see how it looks. And since the CCD can capture images at a high framerate continuosly, most digital cameras can record this data as video, usually along with sound recorded by a small microphone in the camera.

The sensor is smaller than a frame of film, though, so the lens can be scaled down proportionally. Or, if the lens is the same size, it will be gathering more light per area of sensor, so this more intense focusing can allow for the shutter to be open less (which leads to less blur).

How sharp will your image be? That basically depends on two factors: How sharp your lens is (how sharp an image it can project on the sensor), and how harp your sensor is (how much detail it can record if a sharp image is projected onto it). The sensor is made of millions of small photo-sensitive cell clusters, each of which can record the color and brightness of the light falling on it. The more of those clusters you have, the more details you could capture. But, if the clusters are too small and too crammed together, then they start interfering with each other and being thrown off by small signals of light or electricity, which makes the picture look "grainy". So the sharpness of your lens, the number of cell clusters in your sensor, and the grainy-ness of your sensor, are all crucial in determining how sharp the picture is that comes out at the end.

How sharp the lens is has a lot to do with how carefully it is crafted - out of what materials, if any of the elements have aspherical shapes, et cetera. In general, a bigger lens will be much more likely to project an image sharply. So whether a camera's lens is the size of a dime, the size of a quarter, or the size of a small cup, will give you a pretty good idea of how good this lens is at gathering and focusing light. Lenses made by Leica, Carl Zeiss, and other names associated with photography (like Canon, Nikon, Olympus, Fuji, and Kodak) are usually the sharpest. Panasonic cameras have Leica lenses, and some Sonys use Carl Zeiss glass.

The number of cell clusters in the CCD sensor (the "resolution") is measured in megapixels, so that's a dead-easy one. It usually says on the box.

The grainyness of the sensor, although it is as important as the resolution to determining how much detail is captured, is in part dependent on the size of the sensor, and on the resolution of the camera. Smaller sensors, or sensors with more megapixels - in other words, sensors with more pixels per unit area - tend to be grainier. So small cameras, and cameras with 6-8 megapixels, tend to be real grainy. This becomes painfully evident when you make the sensor more sensitive to light (high ISO speed, like 400) for shooting in low light.

(This is the main reason why pictures made by those huge expensive SLR cameras are a lot sharper - their sensors can have as much as 16 times the area of most digital camera sensors, so grain is not a problem at all, even at high ISOs. That, and lenses are typically a whole lot sharper. So an SLR with 6, 4, or even 3 megapixels can take pictures as sharp as those taken by compact digital cameras with twice the number of megapixels).

The EOS Digital Rebel XTi SLR Camera from Canon

The EOS Digital Rebel XTi SLR Camera from Canon packs an array of impressive features and definitive control in a convenient, easy-to-use design. It incorporates a high-resolution CMOS sensor that delivers fine image accuracy with an effective 10.1 MP resolution. Equipped with a 2.5-inch LCD monitor, the camera captures true to life images. The DIGIC II imaging processor ensures natural colors reproduction, precise white balance in any number of lighting situations and enhanced clarity. With the 9-point Wide-Area AF System, the Digital Rebel XTi allows speedy and accurate focusing, for memorable shots in any situation. The Display Off sensor detects the photographer's face against the back panel of the camera, and turns the screen off to prevent the LCD monitor's brightness from disturbing the photographer's eye while looking through the viewfinder. Additionally, the EOS Integrated Cleaning System features a Self Cleaning Sensor Unit to combat against stray dust that enters the camera and adheres to the image sensor during a lens change. Connect your EOS Digital Rebel XTi camera to your computer with a USB 2.0 Hi-Speed connection for fast, hassle-free image uploads. With intuitive simplicity and powerful performance, the EOS Digital Rebel XTi SLR Camera offers style and performance to thrill your senses.

Make money with your digital camera

Its very rare people talk about people making money with image or photo.If you have a digital camera and have some skill in photography why not you use it to upload in the stock photography which you can make money from selling photo when other people download your photo.

But it is not as easy as that.You need to have a good photo before other people want to buy your photo collection.

So why not start now, me be you have a talent.Most of the stock photography are free to join and upload as much as you can your photo collection:

1. Fotolia
2. Dreamstime
3. 123RF
4. StockXpert