Table of Contents
Digital Film or Digital Memory
The next topic in this camera guide is the component that makes the digital camera different from a film camera. The film camera has a back cover or rear cover that opens to the film compartment. The digital camera has a colour LCD, many tiny buttons and controls at the back of the camera body. Digital cameras do not use film and so there is no need for you to open the back to insert film. Instead there is a slot at the side of the camera for insertion of the memory card.
Better digital cameras use removable storage card such as Smart Media card, Compact Flash card, Memory stick, SD Memory card and the XD memory card. The XD memory card is a combined effort of several Japanese manufacturers to design a new memory card that is supposedly more durable, faster, smaller and higher capacity than what is already available in the market.
Which memory card will eventually win the battle of the memory card only time can tell. Many people think that the Compact Flash has higher capacity, is tougher, more durable and is used in most professional cameras. Memory stick - Sony believe they have designed the best storage media but currently it is used mainly in Sony and Samsung products. Sony has upgraded it to Memory Stick Pro to overcome some short coming of the original memory stick. SD Memory card - many think it is the storage card of the future and is currently the most popular memory card in consumer digital cameras. The XD memory card think they can replace all the others! Most of these memory cards have capacity of 512MB to 1GB at the time of writing. The Compact Flash Card has already reached 12GB! However only a handful of cameras can use this high capacity CF card due to the 16bit file system used in most consumer digital cameras. (32bit file system is required to address storage space beyond 2GB capacity!)
Back to our dinosaur age floppy disk - it is a common item. Just insert it in the PC -
How much storage do you need? To calculate the image size of a digital image multiply the resolution in megapixel by three, the product is the storage image size in megabyte. As an example, a 3.3 megapixel image will be about 9.9 MB but a 3.3 megapixel camera only has an effective image size of 3.1 megapixels. Therefore the image size should be 3.1 * 3 = 9.3 MB. Why multiply by three? because colour images are stored as RGB colour components. RGB stands for Red, Green and Blue. Each pixel in a colour photograph is represented by these three channels so we multiply three for each pixel to calculate the image size. The result obtained from this calculation is very close to the storage requirement of a TIFF file. The RAW file is roughly around half to 2/3 of this figure due to a more efficient algorithm used by the RAW format. TIFF and RAW file storage mode are usually available on higher end consumer digital cameras.
From the example you can see it is not practical or economical to save digital images uncompressed as you need a lot of high capacity memory card. Most digital cameras offer compression modes for storage such as super quality mode, high quality mode, standard and economic mode. These different modes are actually different levels of compression in JPEG file format. JPEG file has very good image compression technique in terms of reducing the storage size. However JPEG uses a lossy compression technique. A lossy compression technique reduces file size by discarding unneeded data, resulting in a slight degradation of image quality each time the file is saved and reopened. Just opening a JPEG file do not degrade the image; only when you re-save it. The more compression is required the more data will be discarded thus reducing the size of an image to a very small file but the pay back is lower image quality.
For normal everyday use we suggest saving your images in the super fine or fine mode to reduce image quality loss at the camera. Then when the images are transferred to your PC, resave them to either uncompressed format such as TIFF or lossless compression file format such as PNG. PNG stands for Portable Network Graphics. Images saved in this format are not as compressed as JPEG but it is a compromise between large file and degradation of image quality. If image quality is your concern use the RAW format, if available, to retain originality and maximum quality of the captured image.
Digital cameras without the removable storage are limited to the amount of memory in the camera, usually around 8MB or 16MB. The limited storage is only good for low resolution images and the images are highly compressed to increase the storage. So this type of images may be OK for web pages or as thumb nail images. It is not for real photography but you can still use it for recording purposes such as a camera note book for your blogs or as a party fun camera provided the price is really cheap, otherwise skip this one.
The other half of digital film is the image sensor or CCD. CCD is short for Charged Coupled Device and it converts light into electrical signal or analogue electrical signal. A CCD is an analogue electrical device not a digital device. The digital components and the CPU chip in the camera then convert this analogue signal into digital image. The CCD is made of tiny photo-sensors each one about 1/5 the diameter of your hair! A 3.1 megapixel CCD has 2048 of these sensors across and 1536 sensors vertical, all together there are 3,145,728 sensors and the physical size of this CCD is about 1/3 of an inch square!!
To cut it really short this is how a CCD works. When light falls on the CCD each sensor on the CCD generates different level of electrical signals depending on the light level on each sensor. These electrical signals are then sent to the image processor or CPU of the camera where they are converted to digital images. The sensors in the CCD are like tiny solar cells. They can't retain energy and keep generating different signals depending on the light level, so these images have to be stored on the digital memory card for storage.
Some cameras now use the CMOS image sensor instead of the CCD. Both CCD and CMOS image sensor perform the same function though both have pros and cons. The electronic circuitry for both types of image sensors are also different. The weak spot in either type of image sensors can be overcome or improved by efficient imaging circuity design. For the end-users or consumers they will not notice much differences in both types of image sensors. It is not fair to say the CCD or CMOS is better based on the image quality from two cameras using different sensors as the comparison will be more towards the total imaging system of the camera rather than the sensors alone. What influence a designer and manufacturer more on which image sensor to pick is the production cost, time to market, total product design requirement and future expansion with the company goal more than on imaging quality of the sensor.
Now do you think it is correct to call the memory card digital films or the image sensor digital film? Honestly digital cameras don't need film so why must we still call it digital film; just call it image sensor and digital memory card. Moreover film is a thin, flexible cellulose material!
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