Fundamental of digital images

Digital files can be made by taking pictures with a digital camera or by using a scanner to convert existing prints or negatives into pixel form.

Digital cameras have a grid of sensors, called CCDs (Charge Coupled Device), in the place where traditional cameras would have film. Each sensor measures the brightness and colour of the light that hits it. When the values from all sensors are collected and collated, a digital picture results.

Scanners work in a similar way except that these devices use rows of CCD sensors that move slowly over the original sampling the picture as they go.

Quality aspects in a digital image

The quality of the digital file is determined by two factors:

The number of pixels that governs the amount of details
The number of colour that defines the scope reproduced in the image

One pixel is one dot defined in specific colour. The number of pixels in a picture is represented in two ways B the dimension i.e. the image is 800 x 600 pixels, or the total pixels contained in the image i.e. 480,000 pixels. One million pixels are called mega-pixel. Generally, a file with a large number of pixels will produce a better quality image overall and provide the basis for making larger prints. Currently, there are digital cameras capable of 12 Mega Pixels. Main stream cameras with reasonable price are capable of 3 to 5 Mega pixels.

The second quality consideration is the total number of colours that can be recorded in the file. This value is referred to as the colour bit depth of the image. The current standard is 24-bit colour. A picture with this depth is made up of a selection of a possible 16.7 million colours. I practise this is the minimum of colour needed for an image to appear photographic. In the early years of digital imaging 256 colours or 8-bits was considered the standard. However the colour quality of this type of image is totally unacceptable nowadays. As a matter of fact, modern cameras and scanners are currently capable of 36- or even 48-bit colour. The larger bit depth helps to ensure superior colour and tonal accuracy.

Steps in digital process

The digital imaging process contains three separate steps:

1 Capturing images in a digital format. There are several formats; each format has a specific function and utility. It is at this point that the colour, quality, and detail of the image will be determined. Careful manipulation of either the camera or scanner settings will help ensure that the image contains as much of the original information as possible.

2 Manipulation is where the true power of the digital process becomes evident. Enhancing and altering the colour, contrast, brightness of an image has become as simple as few mouse clicks. Changing the size or shape of a picture can be completed in a few minutes and few complex manipulations like combining two or more images could be achieved fairly quickly. There are numerous to editing software in the market. However, the cost of software can start from free to thousands of pounds. Bare in mind that Adobe Photoshop is the industry standard.

3 Output is where the image will be stored or printed. The image may be used as an illustration in a business report, becomes part of a website, be sent via email as an attachment, projected onto a large screen as a segment in a professional presentation, or the image can be printed as part of publication. There is another way of outputting by authoring images to create a multimedia VCD or DVD.

Drawing objects or vector images

In most photo-editing software there are drawing tools to create hand made images. However, there is a fundamental difference between drawing objects and images captured via digital camera or scanner. Rather than containing the information to completely define each pixel in the image, vector images contain the mathematical instruction to create the image. The file size of a vector images is rather small compared to captured images.

Animation is a series of vector images that differ slightly from each other. Every animation has a beginning and ending point. The frames that show the beginning and the end of the animation are the most important frames in the animation- they are called keyframes. All the frames between the beginning and ending frames are simple variation that bridges the gap between those two keyframes. Vector images are the foundation of animations.

Vector images and animations are rather advance way of creating multimedia.

TWAIN

Twain is a multi-platform scanner interface. A scanner interface has to be launched, used, and closed before being able to edit the scans in application software.

RBG Colour

RBG is the commonly used colour mode. All scanners acquire images in RBG. An RBG file consists of 3 Greyscale colour channels: one red, one green and one blue. Each channel uses 8 bits of data per pixel to display colour, which translates into 256 brightness level per cannel. Therefore, each image is defined by 3 brightness values from 0-256, one for each colour. When all 3 values are 0, the colour is black. When 3 colours are 256, the colour is white. When all 3 are equal numbers between 0 and 256, the colour is some shade of grey. When all three colours are different a specific colour will be created.

Image Formats

BMP

Short for window bitmap, this format is compatible with Microsoft paint. This format is used when handing images over who will continue editing using Paint or another window-based program. BMP files are uncompressed and rather large.

JPEG

Short for Joint Photographic Expert Group (the developer of the format). JPEG powerful compression for photo editing software applications by averaging the colour values of groups of adjacent pixels. Because it always comes at the expense of image quality, it should never be used on image destined for print production. If images are going to be used over the Web, JPEG is perfect. JPEG should never be used in images containing solid colour. JPEG are recompressed every time there are saved, which means, every time a JPEG image is saved, more details are eliminated.

GIF

Because GIF take up very little disc space-they have become the standard for onscreen web graphics. GIF are most appropriate for solid colour such as boxes, buttons, cartoon characters, corporate logos. Only an image with 256 colours or less can be saved as a GIF.

PNG

Portable Network Graphics, the image size falls somewhere between JPEG and GIF. This makes them a better choice for images that are smaller in width and height but contains important details and tones, like highly stylised buttons or online adverts.

TIFF

Tagged Image File Format is the primary file format to used for outputting an Image to paper or films. TIFF uses a type of compression without destroying image data.

Digital film or flash-drive storage device

Digital cameras store images either on internal memory, or on removable memory cards. These are the digital of film, with the crucial difference that images could be wiped out and used again. Less expensive digital cameras tend to store images on internal memory. The advantage of the removable card is it can be removed and connected directly to a pc to download the images instead of linking the camera via parallel port, USB or more modern connections.

The size of the memory card can vary subject to cost. The starting size used to be 1 Mb, however, since some cameras are capable of 5 mega pixel, 1 Mb is no more than a joke. The starting size should not be less than 16 Mb. The latest memory cards could reach 4000Mb or 4 Gigabit and more.

Memory cards are produced by different manufacturers and camera brands use specific memory card.

The available memory cards in the market are:

COMPACTFLASH Card CF

COMPACTFLASHII Card CFII

SMARTMEDIA SM

SECURE DIGITAL Memory Card SD

MULTI MEDIA Card MMC

MICRODRIVE MD

MEMORY STICK MS

NIKON uses CF

SONY uses MS

OLYMPUS uses SM & CF & CFII & MD

CANON uses CF & CFII

MINOLTA uses CF & CFII & MD

FUGIFILM uses CF & CFII & MD &SM

PENTAX uses SM & MMC

All digital camera manufacturers provide a cable to link the camera to the PC. However, this method is rather fiddly and undesirable by most users. The rate of data transfer can be slow or fast subject to the type of cable. The best option is to use digital film readers. The idea is to insert the memory card inside the reader. The reader is linked to the PC via USB cable. The rate of transfer is fairly adequate. To increase the rate of transfer a firewire or USB2 is twenty times faster.

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