Bit Depth

In order select a specific shade of colour within a bit, sampling would be used to get the colour that meets your requirements. In Adobe Photoshop, there is a tool that allows you to do this very easily and is very accurate.

Bit depth can either mean the numbers of bits used to show the colour of a single pixel or the number of bits used for each colour component used in a single pixel. Overall, the bit depth counts how many colours are available in a certain image’s colour palette in terms of the number of bits available. The definition of a ‘Bit’ is the basic unit of information in computing and digital communications. To specify how many different bits are used within a pixel, we refer to this as bits per pixel (bpp).

Every pixel in an image is created through a combination of three different colours, red, green and blue (RGB). These colours are generally referred to as colour channels. The bit depth of each primary colour is known as ‘bits per channel’ (bpc).

When using Adobe Photoshop, there are 8bpp, 16bpp and 32bpp to choose from. The majority of digital cameras have 8-bits per channel and therefore they can use a total of 8 bits per pixels. The table below shows how many colours are available with each bit per pixel. As you can see, when using 8 bits per pixel, there are 256 colours available to use which is a large amount to produce a good coloured image (.GIF file format only supports this amount).

However, higher bits per pixel are available such as 16 bits per pixel which is commonly known as ‘high colour’. These colour depths are sometimes used in smaller digital devices such as mobile phones. In 16 bits per pixel, there can be 4 bits for each red, green and blue and then an extra 4 for transparency. Again, as you can see from the table, 65536 colours are available when using 16 bits per pixel (high colour).

There are also 24 and 32 bits per pixel available which are known as ‘true colour’ and there is 16777216 colours available for each. The only difference between 24bpp and 32bpp is that 32bpp also supports transparency. Usually true colour means that there will be 256 shades of each RGB colour resulting in a better quality image. However, the human eye can only identify 10 million colours and therefore using 24 or 32 bits per pixel might be too excessive.

On the lower end of the scale is 1 bit per pixel which is known as ‘monochrome’. This only includes two colours which are generally black and white.

In order select a specific shade of colour within a bit, sampling would be used to get the colour that meets your requirements. In Adobe Photoshop, there is a tool that allows you to do this very easily and is very accurate.

Vector Images

Vector graphics use geometric primitives (points, lines, curves and shapes or polygon) to create an image on a digital device. Vectors, which can also be called paths or strokes, are lead through certain locations called control points in order to create the image. The central points have a permanent position on the x and y axes and are assigned a colour, a shape, a thickness and also a fill. One of the main advantages of a vector image is that it can be scaled to a large size and will not pixelate. Below is an example of how an object can be scaled and not lose its quality.

Vector images can be generated using a number of different software such as Adobe Illustrator, Adobe Flash and CorelDRAW. As photographic imagery are raster images (include pixels), therefore vector file extension do not support them. There is a large variety of file formats that a vector image can be created in, such as .SVG, .EPS, .FLA, .AI, .CDR, .WMF, and .DRW.

Raster Images

A raster image is used in a certain way to represent digital images and is quite often referred to as a bitmap. There is a wide variety of formats that a raster/bitmap image can be created in, including .gif, .tiff, .jpg, .png, .psd (Photoshop) and .bmp. The image contains many bits of information which then translate into pixels when displayed on the screen. The pixels then convert to form points of colour which creates the overall image.

Each pixel has been given a specific value that decides what colour that pixel is going to be. To assign a colour to the pixel, it uses a RGB (Red, Green and Blue) colour system. There are a total of 256 colour values to choose from allowing it to have a wide range of values.

In order to scale a raster image to a certain size, it all depends on the resolution of the image. If the image was to have a large resolution then it would be able to be viewed on a large scale without any of the pixels being on show. However, if an image had a low resolution, the larger that image got, the easier it would be to see the pixels in which it would be quite difficult to see the image. Below is an example of how pixalated the image is when zoomed in.

 

Raster compression is the process that reduces the size of a raster file resulting in saving space on any system. This can be done in a couple of way; a JPEG file format is a lossy compression method which is mainly used with full colour images and also grey scale images, however, this can lower the quality of the image as pixel values are lost. The other way is to use a LZ77 file which is lossless format where no pixel values are lost.

Pixels

A pixel, which is short for Picture Element, is a single point within a graphic image. A graphic image is made up of thousands or millions of little pixels that are arranged together in rows and columns to produce the entire image. When looking at an image on a digital device, each pixel has its own location in which is represented by dots or squares.  Pixels are packed so tightly together that they appear to be connected; but if you were to zoom in to the image far enough, you would be able to see each individual pixel (Please see image below):

The information stored within a pixel is called ‘bits’. Bits are used to determine how many colours or shades of grey are used within a single pixel. This means, the more bits per pixel (bpp) that are stored within a pixel, the more colours the pixel can display. This all depends on the resolution of the display system to how good the quality of the image will be. On digital devices that can display colour, each pixel in an image is made up of three or four dots which are known as RGB (Red, Green and Blue) or CMYK (Cyan, Magenta, Yellow and Black).

There are two different types of displays in which a pixel can be featured on. There is a CRT (Cathode Ray Tube) display which is a vacuum tube containing several electron guns and a fluorescent screen which is used to view images. The second type of display is LCD (Liquid Crystal Display) which is more common in the modern era. This is a flat panel display that uses the light modulating properties of liquid crystals.

When using a camera to take a picture it is measured in Megapixels; for example, when using a 6 megapixel camera this amounts to there being 6 million pixels in the image taken. Many cameras vary in the amount of megapixels they offer, however, there won’t be much difference between a 5 megapixel camera and a 6 megapixel camera unless it is printed on a large scale.