Unit 30: Task 8: D2

Task 8b

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

print screen 1: file types JPEG, GIF and PNG
print screen 2: compression techniques, all JPEGS at different quantities
print screen 3: colour depth, all Gifs and different colour amounts.

File type: This screen shot shows the different files types; the original image is in the top left hand corner, the JPEG image can be seen in the top right corner, the bottom left shows GIF and the bottom right shows a PNG-8 file format.  The file format that is PNG-8 shows mottling around the image which shows clear blurred effect surrounding the image if you look closely at the image it looks distorted and pix-elated. PNG holds a better quality closest to the original image and is capable of displaying more colour than JPEG.  In comparison to GIF a JPEG is capable of displaying more colours, however when compressed a JPEG file no longer looks as clean and crisp within the photograph. Gif image file formats have a cleaner display when saved however they contain less colour.  

JPEG - will take up 43.94KB
GIF - will take up 159.5KB
PNG-8 - will take up 157.9KB
Original - will take up 732KB

Compression techniques: This screen shot shows the various compression techniques which are available within a JPEG file format. The top left hand corner displays the original image as has been shown in the previous screen shot, on the top right hand corner the image displayed shows a JPEG image file at the highest quality that it can be, at the bottom left it shows the image in a medium quality compression and at the bottom right it the 4-up display shows a low quality JPEG compression image. Compression reduces the amount of space the file will take up on the disk therefore it is squeezed down so that it does not use vasts amounts of disk space. JPEG which is lossy compression shrinks down the image file but with little noticeable effect so the image will remain fractionally the same before it is compressed and saved. Some lossy compression seen with the lowest quality appears jagged and pixelated in areas as the resolution is poor.  The file with the highest quality will require the greatest compression will reduce the file's quality. 

Colour depth: This screen shot displays the colour depths available in a GIF file format and which one will have the best resolution when saving the image. Like the previous two screen shots the top left hand corner is the original image, in the top right hand corner a GIF file with the colour depth of 256 can be seen, in the bottom left a 64 colour depth file and in the bottom right a 16 colour depth file. As seen in the screenshots the GIF file that only has 16 colours has a poor resolution and a weak finish in comparison to the original image it is not as vivid and bold with the colours. The 256 colour GIF displays the vivid colours rather like the original image and has a higher resolution when compared to the 64 colours. When there are more colours (256) being used it also results in a really large file size of 3,786 bytes in comparison to 16 colours which will only have a file size of 1,393 bytes which has a poorer quality than the GIF shown at higher depth.

JPEG files are used mainly to compress images so that they will take up less space when saved onto a disc or hard-drive, to create a small file size the lossless image with have a low quality however to get a good quality file with high resolution the file will essentially be larger and take up more space. It should not be used when creating graphics or texts and only used for photographs.

GIF files are mainly used when regarding colour depth as at and 8-bit colour depth the image will use 256 colours but will loose quality when saved, that is why it is best that GIF's are used mainly for logo's as they require minimum colours and can be saved and compressed into a file that will be smaller than a JPEG and will contain clearer colours than a JPEG image. 

PNG files are used as a substitute for GIF files and can create a transparency to the image and have a small compression size, but will have a slow rate when read and written. It is fairly like a JPEG file as it uses lossless images at a fairly resonable quality.