ESM4714
Scientific Visual Data Analysis and Multimedia
Assignment #2: Shades of Gray
Due: Two weeks from the day it was assigned:
Part I (50pts):
How many different shades of gray can you see?
Instructions:
With PV-wave commands construct a simple procedure file that creates 8 different
windows where each window shows a different number of gray shades. Let the
number of gray shades be chosen as 256/n+1 where n=1,2,4,8,16,32,64 and 128 and
each window starts with 0 (black) at the left most column and ends with 256
(white) in the right most column. Start with the top most window at n=1 or 257
different gray shades with each gray shade occupying a single column which is
only one pixel wide. The next window, drawn below, has n=2 or 129 different gray
shades where each gray region is two pixels wide. The third window is n=4 with
64 different shades of gray and each region is 4 pixels wide. For comparison
draw each window 50 pixel high and stack the windows vertically with n=1 at the
top and n=128 at the bottom. Observe these same gray scale regions with PV-Wave
commands "surface", "shade_surf", and "contour" and comment on how these commands
modify your observations on how many different shades of gray you can detect.
Part II (10pts):
Does the width of gray regions effect your perception
of shades of gray?
Suggestion:
If each gray region within a window must have the same pixel width as the
adjacent regions then each window will have a different horizontal width. For
example when n=1 (the first window at the top) the window will be 257 pixels wide
with 257 different gray shades: 0 (black), and then 1 thru 256(white) regions
where each region is 1 pixel wide. Compare this to n=128 (the last window at the
bottom) where you should have three different regions corresponding to
intensities 0 (black), 128 (gray), and 256 (white) where each region has the same
pixel width of 128 pixels. Obviously the window at the top with n=1 will be a
continuous gradient of gray shades from black to white and the bottom window with
n=128 will not be continuous. Observing gray gradients in the middle windows can
than be used to answer this question.
Part III (10pts):
Can you think of a way to demonstrate that your eyes
are logarithmic sensors when measuring intensity?
No suggestions. You're on your own.
Part IV (20pts):
Implementing what we've learned
Instructions:
Locate filename assign2.dat (two dimensional file 512x200, ASCII integers
(0-255) separated by spaces) in the directory
/optical/ESM4714/assign/assign#2/ on your
optical disk and investigate this data file using PV-Wave commands that you
learned about in Part I (tv, tvscl, contour, surface, shade_surf, etc.).
Describe as much as possible about this data set. Again what conclusions can be
made about gray scale gradients and how they were used on this data set to
"envision information"?
Part V: (10pts):
Post your results on the homework account:
Logon to any Sparc20 in the SMVC, username: homework, password: _______
to be handed out in class.
Create a directory with your lastname:
(~homework/assign#2/lastname).
Put a copy of your PV-Wave procedure file, lastname.pro, in your lastname
directory. Also put a copy of a text file lastname.txt with your comments on
homework assignment#2. Print a copy of your procedure and text files and also hand these
copies in at class on the due date.
Your grade will be based on your observations
conclusions and how well your PV-Wave procedure file works. Your grade will not be
based on your programming skills although brevity, clarity, and meaningful comment
statements will be appreciated.
Click image to return to Visualization home page.
R.D. Kriz
College of Engineering
Virginia Tech
Revised 01/09/99
http://www.sv.vt.edu/classes/ESM4714/Assign/assign2.html