Pixels and Types of Digital Graphics

BTEC Level 3 Games Design

Unit 78-Digital Graphics for Computer Games

Pixel

The term pixel comes from the words picture element, and is the smallest part of an image or display that a computer is capable of displaying. It is the most basic unit programmable colour on a computer image or display. “A pixel is a point sample. It exists only at a point. For a colour picture, a pixel might actually contain three samples, one for each primary colour contributing to the picture at the sampling point.” A quote from Alvy Ray Smith explaining that a pixel is not a square. http://alvyray.com/Memos/CG/Microsoft/6_pixel.pdf      

Picture Resolution

Resolution refers to the number of pixels in an image. Resolution is sometimes identified as the height and width of the image, as well as the total number of pixels in the image. An example of this would be having a picture that is 1080 pixels high and 1920 pixels wide, and that would contain 2073600 Pixels.

Image Resolution

Linking in with picture resolution, image resolution refers to the quality of the image. In basic terms, as the resolution goes up the quality of the image goes up, it becomes more defined and sharper due to the fact that there is more pixels in the same small space. For example, a phone has a certain number of dots in the space of the screen, and the more pixels you have in these dots on the screen, the better the quality of the image as there is more information in the dots.

Intensity

Each pixel that is in the image has a pixel value which determines how bright and/or what colour the pixel should be. In terms of binary images, the pixel has a one-bit number which determines whether it is in the foreground or the background. Continuing on, in grayscale images, the pixel value is a single number that will represent the brightness. The most common format of a pixel is the byte image, where the pixel is given an 8-bit integer ranging from 0-255, where 0 generally represents black, and 255 white, with different scales of grey in-between. In order to represent colour images separate red, green and blue components must be assigned to each pixel, so the pixel value is actually a vector of three numbers.

Types of Digital Graphics

Raster Images

Raster graphics are digital images that have been created or captured as a set of samples in a given space. A raster is a grid of x and y coordinates, and for 3D images then it will also have a z coordinate. A raster image will identify which of these coordinates that they will need to illuminate in either monochrome or colour values. A raster file can also be referred to a bitmap due to the way that the image is mapped out onto the display grid. Raster files are usually larger than vector images, and they are difficult to modify without losing a lot of information. Examples of Raster image file types are BMP, TIFF, GIF and JPEG.

Vector Images

Unlike Raster images, vector images are not made up of a grid of pixels, but are instead comprised of paths that are defined by a start point and end point, with curves, angles and other points along the way. These paths can be a line, or can make up a shape such as a triangle or a square. These paths can be used to create simple drawings or complex shapes. Due to the fact that vector images are not made up of a specific number of dots, they can be blown up to a larger side and not lose any quality. Examples of Vector image file types are AI, EPS, SVG and DRW

File Extensions

A file extension is a way of showing the type of computer file, and gives a clue about what program the file should be opened with. In general, file extensions are three letters long and come after the name of the file. An example of a file extension would be .TXT which just are just text files.

Compression

Compression is a reduction of in the number of bits               

needed to represent data. By compressing data you can save storage capacity, speed file transfer, and can decrease the costs for storage hardware and network bandwidth. Compressing data can be either a lossless or lossy process. Lossless compressions enables you to restore the file to its original state, without the loss of s ingle bit of data. This is generally done with executables, along with text and spreadsheet files as loss of words and numbers would change the information of the file. In comparison, lossy compression permanently deletes redundant data, which is useful for graphics and audio where losing some data bits has no effect on the content.

Image Capture   

There are a lot of different ways to capture images to put into games. For example, you can use cameras and phones to take photos, or you could draw something and then scan it in.

Optimising

When you optimise something you essentially increase efficiency or general performance of something. In images, you have to make sure you get the balance between the size of the image file and the quality of the image right. It is important to think of the target destination of the image; where it will end up. You also have to think about bit depth. By decreasing the bit depth your image will have a smaller file size, but the quality will go down as the volume of colour per pixel will go down, and your image may look dull. Image resolution is also a factor, as having a higher resolution of image will increase the file size, but the quality will also increase as a result. Image dimensions also factor in, changing the height and width of the image will not change the amount of pixels within the image, and they will just have a cover a larger space, making the quality of the image go down.

Storage of Image of Assets

Storage of image assets is very important as it helps with storing things like textures and graphics in order for other people to access them. Making sure they are named appropriately is important in order to help smooth the process, especially when making games as you may have two types of something so it is important that whoever may be using these assets will be able to easily differentiate between the two, even more so when working in teams who all need access to these files. For example, if you are creating a 2D platform game where you will be jumping onto different blocks, you would need to define these different blocks by calling them something like block_red or block_blue. It is important for things to run smoothly in games design as there are a lot of deadlines that have to be met, such as the release date.