Weeks 5&6 - Review questions

1. What's the difference between Lossy and Lossless compression?
A lossy compression is a compression that loses not essential color information. A lossless compression is a compression that doesn't lose any information.
2.What file format would you choose to save a vector graphic that had only 15 colors?
The GIF format
3. Describe two major differences between the JPEG and the GIF.
The JPEG format uses a lossy compression method and supports up to 16 million color, the GIF format use a lossless compression but only support 256 colors.
4. Explain in your own words what color bit depth is.
The color bit depth defines how many colors a monitor will be able to display. One bit has two colours, two bits has 2 to the power of 2 colours, 4 bit, 2 to the power of 4 and so on. So the more bits, the more colors a monitor can display.
5. What is Dithering?
Dithering is a technique that enables you to compensate for the difference in quality when a graphic/picture is used on monitors which display a lesser amount of colours.
6. Explain what the 256 Web-safe color palette is and what it's used for.
A 8-bit monitor, although only used now by a small amount of people, will only display 256 colours. By using the web-safe color palette, you can be sure that the colors of you graphics will display as intended even on an 8-bit monitor.
7. Describe what the term Gamma refers to.Gamma is the brightness of a monitor. It is different whether you use a PC or a Mac computer.
8. What is the recommended Gamma value for graphics?
The recommended value is 2.2 which is between the 1.8 of a Mac and 2.5 of a PC.
9. How can Photoshop help you compensate for Gamma variations?
By lowering the gamma value to between 0.8 to 0.75 in the level adjustment palette. That way the photo will be less bright on a Mac and less dark on a PC.
10. Describe in your own words what weighted optimization is.
It is a technique that enables you to compress different areas of your graphic/image at different quality settings.
11. Please briefly explain how to implement weighted optimization.
In the "Save for the web" page, experiment with different compression settings and see what degrades at what value. Then go back to your graphic/image and create a mask for the areas that will receive the highest quality setting, and another one for the lowest quality setting. Save the selections in different channels. Go back to the Save for the web page and open the save for the Web dialogue box and click the mask icon next to the quality box. Select one of the channel you just created and choose the appropriate quality setting. Then repeat the operation for the other channel.
12. True or False: Both the JPEG and the GIF implement a weighted optimization option for the Lossy setting.
13. What type(s) of compression does the GIF format use?
14. What is a CLUT?
It stands for Color Look-Up Table. It is one of the two methods used to compress a GIF.
15. What does the term Index, in reference to the GIF, refer to?
When a GIF is created, a table of color values is created. That table serves as an index for the color information.