Exercise 5 – File Types & Sizes

Imaging 1
Exercise 5 – File Types & Sizes
Name

ß This is a formative assessment instrument
ß 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
2) TIF file using LZW compression
3) Photoshop .psd file
4) Jpeg file – Quality level 12
5) Jpeg file – Quality level 10
6) Jpeg file – Quality level 5
7) Jpeg file – Quality level 1
8) GIF file – 256 colours – no dithering
9) GIF file – 256 colours – diffusion dither
10) GIF file – 16 colours – diffusion dither

Select ‘Image -> Mode -> Greyscale’ to convert the image to a grayscale image & save as
11) TIF file (no compression)

Select ‘Image -> Mode -> Bitmap’ to convert the image to a bitmap image & save as
12) TIF file (no compression)

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).
The LZW has compressed it to 10MB instead of 15MB

b) When saving a jpeg file what two things change when you select a different quality factor ?
Size of the image as in space and the quality of it

c) What is ‘dithering’ and why is it used ?
Dithering in GIF images helps reduce banding in gradients of color, but it also vastly increases the file size.

d) Explain the difference in size between the greyscale tiff file and the original tiff file.
Original tiff is 15MB and the Greyscale is 5MB this means it has thrown out all the colour pixels and is now only using 256 types of grey