Digital Image Processing

HW1

Yi-Chun Wei Visual Communications LabNational Central University

Mar. 2, 2012

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Outline• Work Chart• Introduction to Bitmap File• Homework Details - Construct color histogram - Color image transform to gray-level image - Resize the image• Grading• Demo Schedule• References

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Work Chart

Extract header

information

512*512

Extract pixel information

Construct the histogram on Y

ChannelHW1-1

Transform to gray-level image

Resize image

512*512

640*480

HW1-2

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Introduction to Bitmap File(1/2)Bitmap File Header

Identifier (ID) 2File Size 4Reserved 4

Bitmap Data Offset 4Bitmap Info Header

Bitmap Header Size 4Width 4Height 4Planes 2

Bits Per Pixel 2Compression 4

Bitmap Data Size 4H-Resolution 4V-Resolution 4Used Colors 4

Important Colors 4Color Table (Palette)

Palette N*4Bitmap Array

Bitmap Data N/A

• Header file

- File header (14 bytes)

- Info header (54 bytes)

• Image content

- Bit array

(pixel information)

• Color table

- ex: a 8 bit image,

N=28

Y. C. Dong, “Digital Image Processing HW1”, 2009

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Introduction to Bitmap File(2/2)

Header + Color paletteHeader54

bytes54 bytes +1024 bytes

Image content

Image content

24-bit Lena 8-bit Lena

Scale: 512*512 Scale: 512*512

Y. C. Dong, “Digital Image Processing HW1”, 2009

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Color Image Transform to Gray-Level Image

 Y = 0.299R + 0.587G + 0.114B

24-bit Lena8-bit Lena

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Gray-level Histogram

Y histogram

number

Blue

196

Green

122

Red

83

Gray level pixel value

Gray level

?

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Resize Image

• P: Desired Point• Q: Known Points (four closet pixels)• R: Point on the line

with known points

Z = A X + B Y + C XY+ D

J. Nett,” Bilinear Interpolation”, 2009.

Bilinear Interpolation:

Gray level value known points

Where A, B, C and D are obtained from the gray-level of the four neighbors.

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Grading• Demo Code (80%) - Extract header file (20%) - Color image transform to gray-level image (20%) - Construct color histogram (20%) - Resize image to 640*480 (20%)• Report (20%) - Plot all your experimental results. (10%) - Describe your finding as rich as possible. (10%)

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Demo Schedule• Thursday night, March , 2012. - Begin around at 19:00 at R3-307.(VCLab)

NOTE: We will use another image to test your code. The details will be announced on our course

website. ( http://140.115.156.251/vclab/html/course/DIP2012.html )

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References• Lena 24-bit color image, 512*512http://www.indinf.pub.ro/catalinp/proiect/lena512.bmp

• About Bmp format websitehttp://en.wikipedia.org/wiki/BMP_file_format (wiki)http://crazycat1130.pixnet.net/blog/post/1345538-%E9%BB%9E%E9%99%A3%E5%9C%96%EF%BC%88bitmap%EF%BC%89%E6%AA%94%E6%A1%88%E6%A0%BC%E5%BC%8F