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Digital Camera Basics - A primer
Digital cameras are confusing to a lot of new users. In this basic guide to digital camera technology we hope to try to give digital beginners at least some basis to use in deciding which digital camera is appropriate for them. When shopping for a digital camera it's at least good to know what the basic terms like white balance, pixel, ppi and dpi mean and how they affect image and print quality. It's also important to know the difference between things like optical zoom and digital zoom as well as the advantages and disadvantages between storage formats such as Compact Flash (CF), Microdrives, Sony Memory Stick, Secure Digital (SD), Multimedia and camera interface technologies such as USB 1.1, USB 2.0 and Firewire IEEE 1394.
A pixel is a contraction if the term PIcture ELement. Digital images are made up of small squares, just like a tile mosaic on your kitchen or bathroom wall. Though a digital photograph looks smooth and continuous just like a regular photograph, it's actually composed of millions of tiny squares as shown below.
Each pixel in the image has a numerical value of between 0 and 255 and is made up of three color channels. So for example a pixel could be 37-red, 76-green and 125-blue and it would then look like this . If it was 162-red, 27-green and 12-blue, it would look like this . There are over 16 million possible combinations using this scheme and each one represents a different color. Computer savvy readers will note that each color in this scheme can be represented by an 8-bit number (byte), so the color of each pixel is defined by three color bytes. This scheme can be expanded, for example to use 16-bits (two 8-bit bytes) for each color. images using three 8-bit values are sometimes called 24-bit color images. images using three 12-bit values for color definition are called 36-bit color images, and those using three 16-bit values are called 48-bit color images.
One of the main ways that manufacturers categorize their digital cameras is in terms of pixel count. What this is is the number of individual pixels that go into making each image. Today this number varies between 1 million (1 Megapixel) to around 14 million (14 Megapixels). A million pixels is abbreviated to MP, so a 1MP camera has 1 million pixels and a 3MP camera has 3 million pixels. Currently most popular consumer digital cameras have between 2MP and 5MP. A 3MP camera can make excellent 4"x6" prints and very good 5"x7" prints. If you intend to make lots of 8"x10" prints, then perhaps a 4MP or 5MP camera would be a better choice. Sometimes two numbers are given, total pixels and effective pixels. Total pixels count every pixel on the sensor surface. Usually the very edge pixels aren't used in the final image. Effective pixels are the number of pixels actually used in the image after the edge pixels have been dropped.
The aspect ratio of a camera is the ratio of the length of the sides of the images. For example, a traditional 35mm film frame is approximately 36mm wide and 24mm HIGH. This has an aspect ratio of 36:24, which can equally well be expressed as 3:2. Some digicams use the same aspect ratio for their digital images. For example most digital SLR (single lens reflex) cameras have a 3:2 aspect ratio. However, video monitors typically use a 4:3 aspect ratio. For example a monitor with a 800x600 display has a 4:3 aspect ratio. With this in mind, most consumer level digicams use a 4:3 aspect ratio for their images.
The size of the digital sensor element (which is equivalent to the size of the negative for film cameras) is pretty small in all consumer digicams - typically around the size of a fingernail (and a small fingernail at that!). As I said above, a 35mm film frame is 24mm high by 36mm wide but most digital cameras use sensors very much smaller than this. Here are some typical digicam sensor sizes. The "name" of the sensor is based on specification for old TV tubes used in the 1950s. Nobody is quite sure why it's being used for modern digital sensors since the "sizes" don't really relate in any consistent way to the actual physical size of the sensor. However these names are widely used, so it's best to know what they are. They are often listed in digital camera spec sheets.
The digital cameras capture images with number of pixels that that image sensor allows. They usually dont have DPI adjustment. However you can adjust capture resolution from 5 Mega Pixel to 1.1 Mega Pixel. Please refer to Page 24 and 25 on the following Owners Manual for this camera.
The DiMAGE 7i has four different image size settings; Full 2560x1920, UXGA 1600x1200, XGA 1280x960 and VGA 640-480. The recorded pixel size in each mode is almost equivalent to an image captured with a 5 mega pixel, a 2 mega-pixel, 1.3 mega-pixel, 0.35 mega-pixel DSC respectively.
The 72 ppi figure is merely an arbitrary starting point used by most image editing software. I've known others to use 300 as a default, e.g. Paint Shop Pro last time I looked at it. Why it should have changed I can't tell at this point, unless you've changed your software; but it's not important.
The figure is meaningless until you want to *print* your images, and even then it's best to just set print size *without* resampling the image, and let the resolution look after itself until you have a need for very large prints.
To see what your camera is capturing, the essential figure you need to be interested in is the images' *pixel dimensions*; and in the case of the CD400 they should be 2272 x 1704 at the camera's full res. setting. (Actually, "resolution" is an unfortunate term, in its popular usage. Resolution really describes how thinly or densely the same pixel count is mapped over the intended physical output size.)
Changing the print size *without* resampling the image will cause the resolution figure (72, 300 or whatever else it might be) to change inversely with the print dimensions, but will not change the overall pixel dimensions of 2272 x 1704.
The camera is not megabytes (MB) but megapixel (MP), there is a big difference. If you multiply the horizontal resolution by the vertical resolution then that will be how many megapixels are being captured. So in this case, max resolution 2048 x 1536 = 3145728 which is 3.1 MP effective. I don't think any camera actually captures exactly the full MP listed on the camera.
Now, if each pixel was represented by a byte then you would have 3.1 MegaByte picture captured. However, each pixel is represented by I think 3 bytes which would give you a 9.3 Megabyte picture captured. However, since this is usually to large for most users to deal with, compression is introduced thus the settings for fine and standard.
The tiff picture type is the 9.3 Megabyte photo with no compression. For most of us this isn't very effective for working with so we use the jpg compression. This reduces the picture to a more manageable size for saving, manipulation and storing. Keep in mind that this is what is called a 'lossy' compression which means that it actually removes pixels from the photograph and uses a technique called interpolation to bring the pixels back later.