Unit 30 D2

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 .jpg images are compressed and the compression often leaves visible signs of compression, which is normally a blocky or speckled appearance. .gif images can only display up to 256 colours, so this means that the quality of the image may be affected. .png images are compressed too but they normally use "lossless compression" so the visual quality can be pretty high. .bmp images are not compressed. They are the best quality file, but also the largest of all files. Image Resolution The image resolution is the pixels. If you have two pictures of the same thing but one is 1024x768 and the other is 640x480, the first will be crisper because it has more pixels per square inch. The more little blocks of colour you can fit into a smaller space, the better quality the image will be. Compression Techniques Graphic file compressors take away pixels, and if you take away too many of them, then the quality of your image is reduced. If one goes too far in the compression, then the picture becomes unrecognizable or is so pixelated it won’t be of any use. Some graphic compressors will give you the option on the compression before you save it to a new file. Colour Depth This is the amount of Bits in an image, colour depth is made from the number of bits in each pixel. Depending on how many bits there is in a pixel, results in the difference of colour depth in certain bits per pixel (bpp), so more shades of a colour can be displayed on the screen. This makes the image look sharper and a better quality than images with less bits per pixel.