This unit covers the basics of digital images, image capture devices and adapters, features of digital images such as bit depth, pixels, measures of image resolution and how they vary based on their purpose whether display or printing.
At the end of this unit you will be able to:
An important aspect of any project aimed at developing electronic digital resources is the production and management of image files. Images, video clips, flash Flash images and animations can be used as a fundamental learning object or as part of more complex Learning Objects. There are various image- capture devices and image-capture capabilities are changing rapidly.
It is important to appreciate the issues surrounding image quality and file formats. These will vary from collection to collection, and will change constantly due to rapid technological developments and emerging standards. In this unit we will look at the features of digital images which will impact file size and resolution. These are important considerations in the generation and dissemination of learning objects that we create.
Pixels, bit depth and graphic file size
Digital images are composed of very small picture elementsâ€”called pixelsâ€”lined up in rows and columns. The size, color and brightness of each pixel determine how the image appears on the computer monitor or printer. Because pixels are the smallest picture elements, the pixel size determines how much detail will appear in the image: the smaller the pixels, the more pixels can appear in a given area, which results in higher resolution.
The pixel size of a file is determined when a digital image is created by the image-capture device and its software. The resolution of computer monitors is defined by the number of pixels found in one row multiplied by the number of pixels found in one column (e.g. 1024 X 780 pixels). Each pixel includes information that must be stored in the computerâ€™s memory or other device.
Therefore, the greater the resolution, the more the number of pixels, and the larger the image file has to be. When the resolution is very low, it results in loss of image information and inaccurate representation of the original image. On the other hand, too high a resolution increases the file size and may not necessarily provide valuable information to the viewer. Large files are also more difficult to maneuver because they take longer to be transmitted or load onto a web page.
Bit depth represents the number of values available to define each pixel. Eight-bit images can display 256 possible values for each pixel, 16â€“bit images can display 65,536 possible values and 24â€“bit images 16,777,216 possible values. Because bit depth is information associated with each pixel, the greater the bit depth, the larger the image file. The human eye has its limitations, so excessive bit depth wastes memory space in digital imaging.
Resolution refers to the dots of ink or electronic pixels that make up a picture when it is printed on paper or displayed on-screen.
Pixel resolution image from: http://en.wikipedia.org/wiki/Image_resolution
Standard high resolution monitors display 1,024 X 780 pixels. The spatial resolution of computer monitors is generally 72 to 100 lines per inch, corresponding to pixel resolutions of 72 to 100 pixels per inch (PPI).