exercise 5.file types and sizes

Name
	§ 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? 14.3m
4. What is the specified resolution of the image? 300
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? 15.1 mb
2) TIF file using LZW compression? 10.6mb
3) Photoshop .psd file? 15 mb
4) Jpeg file – Quality level 1? 4.2 mb
5) Jpeg file – Quality level 10? 1.9 mb
6) Jpeg file – Quality level 5? 680 kb
7) Jpeg file – Quality level 1? 401 kb
8) GIF file – 256 colours – no dithering?	2.9 mb
9) GIF file – 256 colours – diffusion dither?	3.5 mb
10) GIF file – 16 colours – diffusion dither?	1.4 mb

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

11) TIF file (no compression)? 5.1 mb

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

12) TIF file (no compression)? 852 kb

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). b) When saving a jpeg file what two things change when you select a different quality factor ? c) What is ‘dithering’ and why is it used ? d) Explain the difference in size between the greyscale tiff file and the original tiff file.