1. SCANNING FUNDAMENTALS
FifthTuna Data Workshop (TDW-5)
18-22 April 2011, Noumea, New Caledonia
SESSION 7
SCANNING FUNDAMENTALS
This is a brief presentation looking at what we might envisage a regional auditing system of tuna fishery data collection and management systems to involved (or comprise) …
Oceanic Fisheries Programme (OFP)
Secretariat of the Pacific Community (SPC)

2. Scanning Fundamentals – Session Overview
This session will look at
The technical details of scanning
Common problems with scan image quality
Some ways to resolve some scanning problems

3. Scanning Fundamentals – Technical Details
The output and quality of a scan is determined by
The scan resolution
The scanning mode (Black and white, grayscale, colour)
The file type (TIF, PDF, JPG)
The brightness and contrast settings

4. Scanning Fundamentals – Scan Resolution
Scan resolution is usually expressed as DPI (dots per inch)
This represents how many dots, or pixels, are used per inch of the source document.
Typical scanning resolutions are 150, 200, 300, and 600dpi
For Example:
An A4 page is inches long, 8.27 inches wide(21.0x29.7cm)
The number of dots used to create the scanned image can be shown in the following table:
DPI
Dots across page width
Dots along page length
Total dots on page
150
1,240
1,753
2,173,720
200
1,654
2,338
3,867,052
300
2,481
3,507
8,700,768
600
4,962
7,014
34,803,468

5. Scanning Fundamentals – Scan Resolution
Less dots on the page means the dots are bigger, so scanned text will look ‘chunkier’
More dots on the page will mean the dots are smaller, so the scanned text will look smoother
Example (from about 1/2 an inch on the page)
150dpi
200dpi
300dpi

6. Scanning Fundamentals – Scan Resolution
Resolution Summary
Higher DPI (more dots) is better, and gives a smoother and easier to read scan
Higher DPI means more dots = bigger file size!
300dpi scan has 4 times more dots than 150dpi, so the file size can be up to 4 times bigger
600dpi scan has 16 times more dots than 150dpi, so file size also can be 16 times bigger.
We find that the recommended scanning resolutions are:
300 dpi for Black and White scans (more on this next)
200 dpi for Grayscale scans
If file size is not an issue, use 300 dpi

7. Scanning Fundamentals – Scanning Mode
There are 3 main scanning modes
Black and White
Grayscale
Colour
These are often referred to by their ‘Bit Depth’
Bit depth refers to how many ‘bits’ are used per dot (or pixel) of the image, to record the colour. This affects the file size of the image.
Scan mode
Typical Bit depth
# bits in an A4 scan at 300dpi
Size in megabytes (uncompressed)
Black and White 1
8,700,768
1.0 MB
Grayscale 8
69,606,144
8.3 MB
Colour 24
208,818,432
24.9 MB

8. Scanning Fundamentals – Scanning Mode
The more bits there are to record the colour of a dot, the more colours can be shown, and the image will generally look better.
Scan mode
Typical Bit depth
# Colours
Good for
Black and White 1
2 (black or white)
Clear text documents
Grayscale 8
256 shades of gray
Documents
Colour 24
16,777,216
Photos, magazines
Others
Scan mode
Typical Bit depth
# Colours
4-bit Grayscale 4
16 shades of grey
16-bit Colour 16
65,536

9. Scanning Fundamentals – Scanning Mode
Black and White is by far the most economical in terms of file size, but will have problems when scanning images, or light pencil, because for every dot it must decide whether the dot is black or white.
Grayscale is good for scanning images and light pencil
Colour is not necessary for scanning tuna data
Example:
Grayscale
B&W
B&W dark

10. Scanning Fundamentals – Scanning Mode
Scanning Mode Summary
Higher bit-depth (more bits per dot (pixel)) is better, and gives a higher quality and easier to read scan
Higher bit-depth means more dots = bigger file size!
We find that the recommended scanning modes are:
Black and White scans for logsheets that have clear and dark text
Grayscale for pages that have been filled in with pencil, especially light pencil
Slops uses 4-bit grayscale, to reduce the file size
If file size is not an issue, use grayscale

11. Scanning Fundamentals – File types and compression
There are a 3 different file types that are commonly used to save a scan
TIF
JPG/GIF
PDF
Characteristics:
File type
Multiple pages
Best for scanning
Notes
TIF
Yes
Documents
Good for document scanning
JPG/GIF No
Photos and Images
Don’t use for scanning documents
PDF
Documents but OK for images
Good for document scanning, usually embeds the scan as a TIF file

12. Scanning Fundamentals – File types and compression
The files usually use ‘compression’ techniques to make the file size smaller without losing data. TIF has special compression algorithms for different scanning modes:
Characteristics:
Scan mode
Compression algorithm
Uncompressed file size (A4 page scanned at 300dpi)
Typical compressed file size
% of uncompressed size
Black and White
CCITT 4
1.0 MB
100 KB
10%
4-bit Grayscale
LZW
4.1 MB
400 KB
8-bit grayscale
8.3 MB
800 KB

13. Scanning Fundamentals – File types
File Types Summary
TIF and PDF file types are best for scanning documents
Using compression reduces the file size by about 90%
Compression is usually automatic with scanning software, but sometimes is optional

14. Scanning Fundamentals – Brightness and Contrast
The quality of a scan can be enhanced greatly using the brightness and contrast controls of the scanner
These can be changed via the scanning software
They can be used together for the greatest effect

15. Scanning Fundamentals – Brightness and Contrast
Brightness Effects
Brightness Setting
Effect
-100%
Scan is totally black and is unreadable
-50%
Scan is darker, lighter text will be easier to read but page is gray. 0%
Scan is normal brightness
+50%
Scan is lighter, light text might disappear
+100%
Scan is totally white and is unreadable

16. Scanning Fundamentals – Brightness and Contrast
Contrast Effects
Contrast Setting
Effect
-100%
Scan is totally black and is unreadable
-50%
Scan is darker, lighter text will be easier to read, page is gray 0%
Scan is normal
+50%
Scan is lighter, light text might disappear
+100%
Scan is totally white and is unreadable

17. Scanning Fundamentals – Brightness and Contrast
Combined Brightness and Contrast Effects
Brightness Setting
Contrast Setting
Effect 0%
Scan is normal
-40%
+50%
Scan is enhanced, light text is darkened but page is white
-80%
+100%
Light text is greatly enhanced, page still looks white

18. Scanning Fundamentals – Brightness and Contrast
Example:
Brightness -50%
Contast + 75%
Original
Brightness -50%
Brightness +50%

19. Scanning Fundamentals – Brightness and Contrast
Brightness and Contrast Summary
The scan image can be enhanced using the brightness and contrast controls
You can adjust the darkness of an image using either the brightness or the contrast control (e,g, set to -50%), but the entire page will become darker
Adjusting brightness darker, and contrast higher, makes the text on a page darker (e.g. pencil), while keeping the page white
Brightness and contrast have greatest effect on Grayscale images
Slops automatically adjusts brightness and contrast for grayscale images, to enhance the image
Note: The best brightness and contrast settings will vary from scanner to scanner. For the Canon DR-2010C, the best setting is Brightness -80%, Contrast +100%, but this will not necessarily work best with other scanners

20. Scanning Fundamentals – Common Problems
The most common problems with scan image quality are
The writing is not visible
The writing is visible but difficult to read
The file size is too big
The scanning software is confusing or difficult to use
The scans are saved with only one page per file

21. Scanning Fundamentals – Common Problems
The writing is not visible
Causes
The source document has been filled in with a light-coloured pencil
The scanner settings need to be adjusted
How to fix
Scan the document in grayscale
Adjust the brightness and contrast to enhance the writing
Use darker pencil
In SLOPS, choose one of the ‘grayscale’ templates

22. Scanning Fundamentals – Common Problems
The writing is visible but difficult to read
Causes
The scanning resolution is too low
The scan image is not dark enough
How to fix
Increase the resolution of the scan
Adjust the brightness and contrast to enhance the writing

23. Scanning Fundamentals – Common Problems
The File size is too big
Causes
The scanning resolution is too high
The file hasn’t been ‘compressed’
How to fix
Reduce the resolution of the scan
Save using the appropriate compression algorithm (e.g. CCIT 4 for black and white TIF files)

24. Scanning Fundamentals – Common Problems
The scanning software is confusing or difficult to use
A lot of scanning software are complicated and can be difficult to use
Hopefully this presentation will explain some of the technical terms you will encounter with scanning software and make it easier to follow
SLOPS takes the complication out of scanning, so it is recommended to use this software
The scans are saved one page to a file (i.e. if 40 logsheets are scanned, the result is 40 files, rather than 1 file with 40 pages)
The scanning software settings need to be changed

25. Scanning Fundamentals – Summary
The main elements of are scan are
Scan resolution, in dpi, e.g. 200dpi, 300dpi.
Scanning mode (related to bit-depth), e.g. black and white, grayscale.
The file type, TIF, PDF.
Brightness and contrast settings, to enhance the writing in a scanned document

26. Scanning Fundamentals – Summary
OFP Recommended settings
Logsheets that are clear to read and have dark writing
Black and white, 300dpi, multi-page TIF or PDF
Scans filled in with pencil and / or on waterproof paper (e.g. port sampling or observer samples)
Grayscale, 200dpi (or 300dpi), multi-page TIF or PDF
Brightness and contrast set to enhance writing
Recommended software
SLOPS, which makes scanning easier by applying all the settings for you (resolution, scan mode, brightness and contrast, file type, compression)