Images for the Web 1: Review Module D22c (Answers added and 
questions revised 19 June 2000.) 


QUESTIONS 

1. Why is it important to achieve small file size in Web imaging? 


2. What are the types of image representation supported by 
Web browsers? 


3. What does the abbreviation JPEG stand for? 


4. How did the JPEG image format become a standard? 




5. How does the JPEG format compresses images? 



6. What degrees of compression are generally available with JPEG? 



7. What effect does high compression have on JPEG image quality? 



8. What are the two ways in which JPEG images can be rendered on a 
screen? 



9. What types of image is JPEG best suited for? 


10. What does the abbreviation GIF stand for? 


11. What is the origin of GIF as an imaging standard? 



12. In computer imaging, what is a color palette? 


13. How does GIF use color palettes to compress images? 



14. What is the mathematical compression algorithm used by GIF 
images? 


15. What is "transparency" in computer imaging? 


16. To what extent can transparency be implemented in the GIF 
standard? 


17. How are images animated? 



18. How is animation implemented in GIF images? 



19. What is the simplest way to reduce the file size of a GIF 
image without changing the image's apparent size? 


20. What licensing and patent issues are involved in using GIF 
images? 




21. What does the abbreviation PNG stand for? 


22. What is the origin of PNG as a graphic standard? 


23. What features are implemented in the PNG standard that are not 
available in GIF or JPEG? 







ANSWERS 

1. To reduce download time and storage space 

2. GIF, JPEG, and some types of PNG. 

3. Joint Photographic Experts Group 

4. Need to combine more than 256 colors and small file size led a 
group of engineers from the graphics industry to get together in 
the late 1980s. This group sought and received recognition from 
ISO (International Organization for Standards), and ITU 
(Interneational Telecommuniations Union), which eventually 
approved the JPEG specifications as a standard. 

5. Each group of 64 pixels (8x8) is analyzed for the most 
significant color contrasts. These are represented digitally, and 
the resulting code is then compressed using the Huffman encoding 
compression technique. 

6. 0 to 100% 


7. The image becomes blurred with seemingly random spots of color 
surrounding objects of contrasting color. 


8. "Standard" (picture is built top-to-bottom) and "progressive" 
(entire picture comes gradually into focus). 


9. Photographs of people and landscapes; graphics with broad-
spectrum color gradients. 


10. Graphic Interchange Format 


11. It was developed by CompuServe in the mid-1980s to speed image 
download times for their on-line customers. 


12. A list of the colors available for the pixels in an image. 


13. Pixels are indexed to a particular palette color. The smaller 
the palette, the fewer the bits needed to represent a pixel. 


14. LZW (Lempel-Ziv-Welch) compression 


15. Pixels in an image take on the color of the pixels in the 
layer below them. 


16. One level of transparency is available: complete transparency. 


17. A series of images is created, and each is shown in turn to 
provide the illusion of motion. 


18. The GIF file contains a series of images together with 
information about how frequently they should be changed, how many 
times to loop through the set, etc. 


19. Reduce the number of colors. 


20. GIF technology is patented by CompuServe; LZW compression is 
patented by UniSys. It is legally required that designers of 
images stored as GIFs pay a royalty; this is done through purchase 
of the graphics program that was used to convert the image to GIF. 


21. Portable Network Graphics 


22.  


23. PNG incorporates image layers and multiple levels of 
transparency.