1. Getting Image Data Image Data Files 11/15/2018
Copyright Gene A Tagliarini, PhD

2. Copyright Gene A Tagliarini, PhD
Common Issues
Identifying the image file type
File organization
Data compression
Structural information
How many sub-images
How are they to be rendered
Notations
11/15/2018
Copyright Gene A Tagliarini, PhD

3. Typical File Organization
Header
File identifier
Image parameters (height, width, layers, compression scheme, etc.)
Data
Color table
Explicit sample data
11/15/2018
Copyright Gene A Tagliarini, PhD

4. Copyright Gene A Tagliarini, PhD
Example 1: ARF Files
11/15/2018
Copyright Gene A Tagliarini, PhD

5. Example 1: ARF Files (cont’d)
Header
Contains 32 bytes (here indexed 0-31)
Bytes 8-11 represent the image height
Bytes represent the image width
Data
A single linear list of (height * width) pixel intensities
11/15/2018
Copyright Gene A Tagliarini, PhD

6. Example 1: ARF Files (cont’d)
How large would a file be?
Assume
Width = 640
Height = 480
Pixel intensities from (fit in an unsigned byte)
Header = 32 bytes
File size = 307,232 bytes = 640*
11/15/2018
Copyright Gene A Tagliarini, PhD

7. Example 1: ARF Files (cont’d)
11/15/2018
Copyright Gene A Tagliarini, PhD

8. What about color image files?
11/15/2018
Copyright Gene A Tagliarini, PhD

9. Copyright Gene A Tagliarini, PhD
A Color Vision Model
11/15/2018
Copyright Gene A Tagliarini, PhD

10. Copyright Gene A Tagliarini, PhD
Example 2: BMP Files
11/15/2018
Copyright Gene A Tagliarini, PhD

11. Example 2: BMP Files (cont’d)
Common but not parsimonious
Permits
Color tables
Various numbers bits per pixel
Explicit color specification for each pixel
Compression (rarely encountered)
11/15/2018
Copyright Gene A Tagliarini, PhD

12. Example 2: BMP Files (cont’d)
Header Information
Offset
Field
Size
Content
0x0
Identifier 2
Type of BMP (ASCII “BM” i.e., 66,77 = bitmap)
0x2
File size 4
Total number of bytes in the file
0x6
Reserved
For future use
0xA
Data offset
Offset from beginning of file to start of data (in bytes)
0xE
Header size
Total number of bytes in the information header
0x12
Width
Bitmap width in pixels
0x16
Height
Bitmap height in pixels
0x1A
Planes
Number of planes
11/15/2018
Copyright Gene A Tagliarini, PhD

13. Example 2: BMP Files (cont’d)
Header Information
Offset
Field
Size
Content
0x1C
Bits per pixel 2
Possible values:
1 – Monochrome image
4 – 16 color bitmap
8 – 256 color bitmap
16 – 16-bit (high color) bitmap
24 – 24-bit (true color) bitmap
32 – 32-bit (true color) bitmap
0x1E
Compression 4
Compression specification (0 means no compression)
0x22
Bitmap data size
Size of data in bytes (rounded up to the nearest even multiple of four bytes)
0x26
HResolution
Horizontal resolution in pixels/meter
0x2A
VResolution
Vertical resolution in pixels/meter
11/15/2018
Copyright Gene A Tagliarini, PhD

14. Example 2: BMP Files (cont’d)
Header Information
Offset
Field
Size
Content
0x2E
Colors 4
Number of colors used; for 8-bits/pixel this value will be 256 (0x100)
0x32
Important Colors
Value = Colors when all are important
0x36
Palette
N*4
bytes
Palette specification. Four bytes for each color in the palette
1 byte for the blue component
1 byte for the green component
1 byte for the red component
1 byte for fill to double word boundary (= 0x00)
0x436
Bitmap data
X bytes
Depends upon compression scheme; points to values in the palette or gives explicit values for the blue, green, and red components
11/15/2018
Copyright Gene A Tagliarini, PhD