Exercise 5 – File Types & Sizes

	Imaging 1
f	Exercise 5 – File Types & Sizes
Name	Paul Livingston
	§ This is a formative assessment instrument § You must be rated ‘Competent’ in this assessment item.
Learning Outcomes	Learning Outcome 6 - Identifying and define a range of file types and describe their uses, and compare and evaluate methods of uploading digital files using general operating systems and dedicated imaging software.
Tasks	1) Copy the file ‘Img 1 – Ex 5 – Image.tif’ from eLearn to ‘yourname-Ex5’. (Remember to delete this file when you have completed this exercise). 2) Open the file ‘Img 1 – Ex 5 – Image.tif’ in Photoshop and do the following :- Select ‘Image -> Image Size …’ :-

1. Width of the image in pixels	2500
2. Height of the image in pixels	2000
3. Calculate the size of the image in Megapixels	5MP
4. What is the specified resolution of the image	300 ppi
5. Width of the image in cm	21.17
6. Height of the image in cm	16.93

Select ‘File -> Save As…’ and save the image in the following formats. Name the files to clearly identify them.

After each save close the image and reopen to save to the next format. Use the Finder/File Browser to record the sizes of the files created.

1) The original .tif file	15 MB
2) TIF file using LZW compression	10.4
3) Photoshop .psd file	15MB
4) Jpeg file – Quality level 12	4.2MB
5) Jpeg file – Quality level 10	1.9MB
6) Jpeg file – Quality level 5	680KB
7) Jpeg file – Quality level 1	401KB
8) GIF file – 256 colours – no dithering	2.9MB
9) GIF file – 256 colours – diffusion dither	3.5MB
10) GIF file – 16 colours – diffusion dither	1.4MB

Select ‘Image -> Mode -> Greyscale’ to convert the image to a grayscale image & save as

11) TIF file (no compression)

5.1MB

Select ‘Image -> Mode -> Bitmap’ to convert the image to a bitmap image & save as

12) TIF file (no compression)

741KB

3) Discuss the following with the class and post the answers on your blog :- a) Explain the difference in the sizes of the two tiff files in steps 1) and 2). LZW is a lossless compression. That is it compresses the size of the file without loss of data using a lookup algorithm. b) When saving a jpeg file what two things change when you select a different quality factor? Size of the file and quality of the image that limits the ability to enlarge. It also reduces the colour values as you select lower quality factors. c) What is ‘dithering’ and why is it used ? The positioning of different coloured pixels within an image that uses a 256-colour palette to simulate a colour that does not exist in the palette. A dithered image often looks 'noisy', or composed of scattered pixels. Google definition viewed 28 March 2011 <publications.europa.eu/vademecum/vademecum/9313fdfe-c49e-119e-45c6a6441e63e066_en.html> d) Explain the difference in size between the greyscale tiff file and the original tiff file. The greyscale is an 8 bit file while the original is a 24 bit file (8 bit per channel).