Weeks 5 and 6 Labs
Part 1 Website Interface
Part 2 Graphics study
Original psd. I created the selection using paths then converted the path to a selection and saved the selection as a channel. I added the selection using the brush tool.
Weeks 5 and 6 Review Questions
1. What's the difference between Lossy and Lossless compression?
Lossless compression retains the same properties of an image after compression. Lossy results in a lower quality image after compression due to the loss of non essential colour information.
2. What file format would you choose to save a vector graphic that had only 15 colors?
It's likely you would chose to save a vector graphic with only 15 colours as a GIF file. This lossless compression format would keep the image size down but the detail high.
3. Describe two major differences between the JPEG and the GIF.
JPEG is a lossy compression and GIF is lossless. JPEG files can store up to 16 million colours whereas GIF is restricted to 256. Because of this JPEG is primarily used for detailed images such as photographs and GIF is used for vector based images and graphics .
4. Explain in your own words what color bit depth is.
The colour bit depth is the number of colours per pixel. The higher the bit colour depth the more colours that can be displayed. The higher the bit depth, the more colour detail which will be displayed.
5. What is Dithering?
Dithering is the process which is used when an application cannot display the full range of colours in an image. This normally happens because monitors display differently.
6. Explain what the 256 Web-safe color palette is and what it's used for.
The 256 web-safe palette is the 256 colours which are correctly diplayed on a 8 bit computer system. This palette is not as topical as it used to be as the vast majority of computer users now have a systems that have 16/32 bit but you should bear it in mind depending on who you are designing for, for example PDA's and cell phones tend to be limited to 1 or 8 bit color.
7. Describe what the term Gamma refers to.
Gamma is the difference in brightness between PC's and Macs monitors
8. What is the recommended Gamma value for graphics?
The recommended Gamma value for Graphics is 2.2
9. How can Photoshop help you compensate for Gamma variations?
You can add an adjustment layer if levels and lower the Gamma vakye in the centre to between 0.75 and 0.8. You can also dook at the graphic on view>proof set-up and choose either Mac or Windows RGB.
10. Describe in your own words what weighted optimization is.
Weighted optimiseation is using different compession rates for different areas of an image.
11. Please briefly explain how to implement weighted optimization.
Create a selection mask, the selected (white) areas will receive the highest comression ratio and the unselected areas will receive the lowest. Use save for web, hit the use channel as selection icon, select the alpha channel from the drop down menu then set the maximum and minimum quality settings using the black and white sliders (or input values).
12. True or False: Both the JPEG and the GIF implement a weighted optimization option for the Lossy setting.
True, you can implement weighted optimisation for Lossy settings in both file formats.
13.What type(s) of compression does the GIF format use?
GIF uses a lossless form of compression. With the save for web setting you can choose to implement a lossy setting to further reduce file size.
14. What is a CLUT?
Colour Look Up Table which is used by GIF to identify colour values for the image. By not having to save each pixels data smaller file sizes are achieved.
15. What does the term Index, in reference to the GIF, refer to?
You apply indexing to a file, but you do this directly to the psd file which you then save as a GIF