Unit 30 D2

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.

File format – File format has an impact on file size and image quality because there are different file types for different compression methods. JPG uses a compression method that analyses blocks of 8x8 pixels, but depending on the image, 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 as the original otherwise it is impossible to get the original quality back. As shown in the picture, 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.

Image resolution – Image resolution will have an impact on file size and image quality because changing Image resolution is measure in DPI, 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 as well as this it also effects the quality of the image this is due to 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,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. 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.

Compression techniques – Compression techniques effect both file size and image quality. Compressed files are significantly smaller than their uncompressed files,they fall into two general categories known as: "Lossy" and "Lossless". Lossless compression ensures that all image information is preserved, even if the file size is a bit larger as a result. It never discards information about the original image. Lossy compression, by contrast can create file sizes that are significantly smaller, however achieves this by selectively discarding image data. Lossy compression creates smaller files by losing some information about the original image. It removes details and color changes it deems too small for the human eye to differentiate. Lossy compression results in pixels and resolution lost after compression, this is so the file can be used more efficiently and at a lower file size.