COMPUTER VISION 600.461
WEB PAGE IS UP !!
http://www.cs.jhu.edu/~wolff/course600.461/index.html
OR
Simply go to computer science homepage and go to
homepage for Lawrence Wolff and look for link.
September 21, 1998
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HOMEWORK POLICY
• This year homework assignments for the
most part will be ‘handed-in’ on the web.
This requires at the least that:
– You have a web homepage.
– You add a link COMPUTER VISION 600.461
to your homepage that points to the appropriate
homework assignment being handed in.
– You require a password to access the link to
your respective homework assignments.
September 21, 1998
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HOMEWORK POLICY
• A page will be maintained (linked to course
600.461 homepage) with a list of grades
cross-referenced against the last 4 digits of
your Social Security #.
• The usual rules regarding university policy
on cheating will be strictly enforced.
September 21, 1998
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HOMEWORK ASSIGNMENT
Due Wed. Sept. 23
• This is a really easy first homework
assignment that acquaints you with a
popular and a really useful image display
tool called ‘XV’
• Works on popular ‘Command Line’
environments such as UNIX and on DECs
and SGIs.
• If you don’t already have this you can ftp
September
21, 1998
4
from
ftp://ftp.cis.upenn.edu/pub/xv
HOMEWORK ASSIGNMENT
Due Wed. Sept. 23
• Access image files desert.gif, peppers.gif and trees.gif
displayed on Computer Vision course 600.461 homepage.
• Display the image trees.gif and enhance contrast using
‘gamma=3.0’ and ‘gamma=5.0’ intensity correction.
• Segment trees.gif into a binary image using respective grey
level thresholds 50, 100 and 150.
• Display desert.gif and peppers.gif, respectively, and resave
these images using jpeg achieving a 10:1 compression.
September 21, 1998
5
IMAGE FILE FORMATS
BITMAP IMAGES
(raster images)
I(r,c)
VECTOR IMAGES
While key points of a vector
image are represented, this must
ultimately be displayed as a bitmapped
image called a rendering.
(r2,c2)
row
(r1,c1)
column
September 21, 1998
(r3,c3)
6
IMAGE FILE FORMATS
Image files usually include the following
information:
• Header
–
–
–
–
–
–
number of rows (height)
number of columns (width)
number of bands*
number of bits per pixel
file type (magic number)
type of compression *
• Image Data
September 21, 1998
*optional but frequently
7
used.
SOME COMMONLY USED IMAGE
FORMATS
• BIN
– raw data, no header
– user must incorporate header information for
applications.
• PPM
– PBM (binary), PGM (gray-scale), PPM (color),
PNM (handles all of the above)
– headers consist of ‘magic number’ for file type,
image width, image height, number of bands,
and, maximum brightness which determines
September 21, 1998
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required number of bits/pixel
GIF IMAGE FORMAT
• GIF (Graphics Interchange Format)
– Limited to 8 bits/pixel for both color and grayscale.
8-bit index RED
0
R0
BLUE
G0
B0
R1
R2
G1
G2
B1
B2
254
R254
G254
B254
255
R255
G255
B255
1
2
September 21, 1998
GREEN
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TIFF IMAGE FORMAT
• TIFF (Tagged Image File Format)
– More general than GIF
– Allows 24 bits/pixel
– Supports 5 types of image compression
including:
• RLE (Run length encoding)
• LZW (Lempel-Ziv-Welch)
• JPEG (Joint Photographic Experts Group)
September 21, 1998
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IMAGE COMPRESSION
• Compression Ratio
– (Uncompressed File Size)/(Compressed File
Size)
• Bits per Pixel
– (Number of bits)/(Number of pixels)
September 21, 1998
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