Part 3. Image Optimisation

Target Image Output

The target image output is the output of an image for its target. For example if an image’s target is for a poster the image resolution must be higher than that of a business card.
The Target image output should set aside a certain amount of dpi to minimise the loading times.

Image bit-depth

Image bit-depth is the number of bits used to show the colour of singular pixels in a bitmap image. The more bits within the image the better the quality in the image. The simplest of bit images, a 1 bit image, can only show 2 colours black and white. That is because the 1 bit can only store one of two values 0 and 1 (black and white). An 8 bit image can store up to 256 colours whereas a 24 bit image can store up to around 16 million colours.

The image bit-depth can also determine the image size along with the image resolution. With the increase of bit depth, the increase in the image size. This is because more colour information has to be stored for each pixel within the image.
Photoshop has a good image depth of 32 bits per pixel, for HDR (high-dynamic-range) images, however most commonly uses 16-bit, meaning the overall quality of the image increases with more depth. A 32-bit image can make use of up to 4.295 million colours.

Image Resolution

The image resolution often refers to the image quality, sharpness and clarity. The term Image resolution is often used to describe monitors and printers. A good example is a printer with a 300-dpi (dots per inch) is capable of printing 300 different dots per line an inch long.

With graphics monitors, the screen resolution is the number of pixels on the entire screen. For example a screen that is 1920x1200 resolution would have 1920 distinctive pixels on each of the 1200 lines. This would mean there is about 2million pixels on the screen at the same time. There are different types of classification for resolutions, high-resolution medium-resolution and low-resolution.

Image Dimensions

Image dimensions are the length and width of the digital image. Dimensions can be seen like image resolution however with some software, such as Photoshop, you can scale your work area according to your desire, by inches and centimetres.  Image dimension is good when designing to a specific measurement, such as a CD, DVD or Blu-ray case. These cases are measured out by centimetres or inches. Within Photoshop you can select your document to be those specific dimensions so you can meet the specific criteria.

Image Compression

For your target hardware, it is important to optimise for digital graphics. Higher quality uncompressed images will not render without enough memory.  Images need to be compressed according to hardware, for example, the Xbox 360 only has 512MB so that textures will need to be compressed, whereas a high end PC will have a larger memory so the API will stand in.

The technique is used to reduce file size by taking the original file and compressing it down so it can be made into a more transferable file. This means that when transferring a file the file will be quicker to transfer over the internet and take a shorter time to download. A good example is when using e-mail. E-mails can only attach up to a limit, which therefore means that large files cannot be sent across with e-mail. With compression you can compress the file by up to half its size and send it.

Files can be compressed using some programs such as WinZip, WinZip will compress the folder into a ZP format which will reduce the size however keep the quality the same. This type of compression is the lossless compression type as it compresses the folder and loses none of its quality or any files within the compression.