2. Why Digital?
The ability to easily preview pictures and delete any bad shots, and know immediately if a particular photo needs to be re-shot
The costs of film are replaced with memory cards/sticks that can be re-used again and again, with the larger cards/sticks having a capacity of thousands of pictures
Since pictures are saved on memory cards/sticks, you can easily share pictures by copying off the photos, or sharing the card/stick
Decisions on effects like cropping, sepia tones or black and white, can be easily made after the picture has already been taken

3. Pixels
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.

5. Pixel Count
The number of individual pixels that go into making each image
A million pixels is abbreviated to MP, so a 1MP camera has 1 million pixels and a 3MP camera has 3 million pixels
3MP
4MP
5MP
Largest Image (typical)
2048 x 1536
2272 x 1712
2592 x 1944
Print size at 320dpi
6.5" x 4.8"
7.1" x 5.4"
8.1" x 6.1"
Print size at 240dpi
8.5" x 6.4"
9.5" x 7.1"
10.8" x 8.1"

6. Image Resolution
Maximum Print Size
less than 640X480
Wallet size only
640X480
absolute largest, 4X6
1024X768
4X6
1152X864
5X7
1600X1200
8X10

7. Resolution Is the amount of detail the camera will be able to capture.
The more pixels in the camera’s receptor, the more detail the camera will be able to capture and print out in larger high-quality prints.
Most newer entry level models start at about 3MP.
Cameras with 5MP or higher will allow you to make clear prints in larger sizes, and giving you the freedom to crop an image later without significantly losing quality.
Higher mega pixel cameras are a benefit because when you go in and edit something, and blow it back up to regular size, you lose some of the resolution.

9. Aspect Ratio
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.
However, video monitors typically use a 4:3 aspect ratio.

10. Digital Zoom and Optical Zoom
Optical zoom works just like a zoom lens on a film camera. The lens changes focal length and magnification as it is zoomed. Image quality stays high throughout the zoom range.
Digital zoom simply crops the image to a smaller size, then enlarges the cropped portion to fill the frame again. Digital zoom results in a significant loss of quality.

12. File Types JPEG, TIFF and RAW
The size of the digital file corresponding to the image which the camera produces depends on the pixel count.
The files can be big and they can be compressed quite a lot without a significant drop in quality.

13. Compression Types
A lossy compression method is one where compressing data and then decompressing it retrieves data that may well be different from the original, but is close enough to be useful in some way
Lossless data compression is a class of data compression algorithms that allows the exact original data to be reconstructed from the compressed data. Lossless compression is used when it is important that the original and the decompressed data be identical.

14. Joint Photo Experts Group
JPEG is an algorithm designed to work with continuous tone photographic images) which takes image data and compresses it in a lossy manner (this means you do lose some information)
The more you compress, the smaller the file but the more information you lose

15. On the left, 10:1 JPEG compression. On the Right 40:1 compression.
Uncompressed the image would look virtually identical to the 10:1 JPEG on the left.

16. Tagged Image File Format
There are also lossless ways of saving files using TIFF
These keep all the original information, but at the cost of much bigger files

17. RAW
Some cameras offer a third option, that of saving the actual data generated by the sensor in a proprietary format
These files are compressed, but in a non-lossy manner. They are significantly smaller than equivalent TIFF files, but larger than JPEGs.

18. Display, Printing, DPI and PPI
When you display a digital image on a monitor, the only thing that determines the size of the image is the pixel count and aspect ratio
PPI stands for "Pixels per inch" and is almost exclusively used for printing, not video display.
DPI stands for "dots per inch" and is a property of a printer, not a digital image

19. Memory
Most cameras ship with memory included, either built in or as a low-capacity memory card that will store a handful of images at your camera’s lowest resolution.
Memory card capacity is measured in megabytes (MB) or even gigabytes (GB).
A 16 MB card is usually included with the camera will hold only 6-8 full-resolution images in a 4-MP camera.
A 256 MB card will hold about 125 full-resolution images.

20. Types of Memory Compact Flash (CF)
Secure Digital (SD) - Very small. They have a built in write protect switch to prevent accidental erasure and certain encryption capabilities of little interest to digital camera owners.
Smart Media - Thinner than CF cards, but lacking an on-card memory controller.
Memory Stick - Introduced by Sony and used only by Sony

21. LCD Screen
A colour LCD screen is a standard feature used to frame your shot, review your photos and view menu functions.
Screens are usually 1 ½ to 2 ½ inches, measured diagonally.
Most cameras also feature optical viewfinders and are handy in the sunlight when LCD’s are sometimes difficult to view.
LCD screens are a big drain on your battery and can be turned off to conserve battery life.

22. Lag Time
Delay between when you press the button and when the photo is actually taken.
This can make it harder to shoot action.
The time between the press and the capture of the image ranges dramatically from model to model.
The more processing the camera has to do, the longer the camera’s lag time.

23. Parts of the Camera
Mode
Dial
Optical
Viewfinder
Lens
Shutter