Unit 30 - D2

Describe and evaluate the impact that file format, compression techniques, image resolution and colour depth have on file size and image quality.

(D2) 

File format – File format has an impact on file size and image quality because there are different file types for different compression methods, and this affects the quality of the image in a few ways. For example, if you save your file as a BMP file, the image is uncompressed, and every pixel is left in its place which leaves the file size big, but the quality is at a maximum. If you save your file as a JPG for example, the file size is smaller, but the quality of the image isn’t that much of a high quality. JPG uses a compression method that analyses blocks of 8x8 pixels and, but depending on what the image is, this could reduce the quality of pixels within a block. It is important to always save the compressed picture as a copy and keep the uncompressed image original because it is impossible to get the original quality back.As shown in the picture below, if you save your image as a JPEG, it will take fewer pixels to save and it saves up a lot of data compared to if you saved it as a GIF or PNG. The image is also a lot better than the others so you can see why people would prefer to save it as a JPEG instead of the other files.

Compression techniques – Compression techniques impact on file size and image quality because any type of compression will reduce the size of an image. There are two main types of compression which describe how they affect images, I researched this and found out that one of them is called ‘Lossy’ compression. This type of compression reduces the size of the image by removing some data from it; this means it will affect the quality of the image. The other compression type is ‘Lossless’ compression, this type of compression reduces the size of the image by changing the way in which the data is stored, so this shouldn’t make any changes to the image that has been made.

Image resolution – image resolution will have an impact on file size and image quality because changing Image resolution is measure in DPI, which is Dots Per Inch, this means that if you increase the resolution then the DPI will increase and the quality of the image will get better because there are more pixels that make up the image, so this should make this image more professional. When the image resolution is increased the image has more pixels, and as I found out this means that the file will get a lot bigger as the number of pixels increases. But decreasing the resolution will make the image quality lower but will reduce the file size.

Colour depth – Colour depth has an impact on file size and the image quality because it is used to describe the maximum number of colours that are used in the image. If there is a high amount of colours then the image will look more realistic when it is done. With bitmap images, the colour depth will affect the final file size. The amount of colours an image can contain depends on the bit depth of its pixels. The higher the bit depth value, the more colour information each pixel can display and the greater the number of colours the image can contain. When finding out how colour depth has an impact on file size and image quality, I learnt that the RGB colour mode contains 8 bits in each of its three colour channels which are red, green and blue, this gives the RGB image a colour depth of 24 bits (8 bits per channel x 3 channels). These will affect the quality of the image because it is up to you how much colour you want to put on the image, you can make it more shaded in other parts, or maybe add affects which could turn it black and white or even in a faded like image.