A.D.I.E.M ©
Bob DiNatale
Scanning... Reading: Chapters 4 & 5 Studio Techniques by Ben Wilmore
  "The difference between failure and success is doing a thing
nearly right and doing it exactly right. - Edward C. Simmons 		 
Optimizing scans INPUT into a computer has everything to do with knowing the final OUTPUT!
File Resolution Chart for Output Media [For a test to optimize your own system, Click here]
Output Media: File Resolution: [PPI Scan Rate x Scanned Area x Scaling]

Epson Photo Printer
Magazines and Brochures
Newspapers
35mm Slides
E-mail
Web Pages
PowerPoint Presentation

 150 pixels per inch
266 pixels per inch
125 pixels per inch
2400 pixels per inch
320 pixels [.JPG medium or low]
# of pixels dictated by page design [.JPG medium or low]
800 pixels [.JPG medium or high]
...Doing the "Activity" below may be helpful to better understand "File Resolution" -
Scanning Methods:
A good scanning software should have the ability to: 1) enter "dpi" resolution; 2) have a selection bounding with the ability to enter values and the option to "lock" " these input values; 3) enter a scaling factor; 4) enter the output size in either inches or pixels.
Methods 1 & 2 are not recommended but need to be mentioned. Methods 3 & 4 are the best and require a bit more understanding of output resolution requirements. Methods 3 & 4 require scanning software with the ability to enter INPUT, SCALING and OUTPUT settings.
revision 2

Method 1 ...getting the most your system can give!
1 - Set DPI at maximum scan rate
2 - Select desired area with "bounding box" and scan.
The run and gun approach... it's like using an 8x10 Deerdoff to shoot passport photo. You will create the biggest files which is necessary for the "best" and "largest" output you can achieve with your system (scanner and original sample size). It will also tax your system for memory, storage space and processing time. The first step in Photoshop with a file produced in this manner is to "Resample Image" [bicubic] for the final output media then continue with your work.

Method 2 ...scanning software that has No scaling and No Output settings!
1 - Set DPI at desired scan rate (if available)
2 - Select desired area with "bounding box" and scan.
3 - Set "output" quality... Good luck!
Settings are something like "Good / Better / Best". This is to make it easy for beginners but the lack of controls soon leads to frustration ...try to find another software or mode setting.

Method 3 ...Scanning software allows setting INPUT, SCALING and OUTPUT! [most common]
1 - Set the resolution DPI for Output medium (see File Resolution Chart above)
2 - Preview original sample and select the desired area with "bounding box" [input]
3 - Enter in final print size in inches [output] ...the software will calculate the scaling necessary.
4 - Scan
This will create a "file resolution" that when opened in Photoshop will produce an "Images Size" of the desired size and resolution.
e.g. If you set a scan rate at 150dpi (desired print resolution on my Epson), then select an area to scan with the bounding box, then set an output of 10 inches (desired final print size) ...it will produce a "file resolution" at a print size that is exactly what you need!

Method 4 ...Scanning software with INPUT, SCALING and OUTPUT settings! [My Way]
Before starting set your output units to "pixels"...
1 - Determine final pixels needed for output need [ppi x inches] - (see File Resolution Chart above)
2 - Preview original and select the desired area with "bounding box"[input]
3 - Enter Pixels needed [output]... the software will calculate the scaling necessary.
4 - Scan
When viewing "Images Size" in Photoshop, don't worry about the Print Size and Pixels/inch... when you set the "Print Size" (with "Resample Image"unchecked) the Pixels/inch will fall into place.
If scanning software does not allow scaling input or is optimized for 100% scaling:
2a - Enter scan resolution 100dpi
3a - Note % scaling calculated by the software. Changing scan resolution to the scaling factor # and entering the scaling to 100% will produce the same pixel output.

Power TIP! ...Setting aspect ratio of the final print during the scanning process!
Ever scan an area of a photo or slide and after "doing your Photoshop thing" you get ready to print the file only to find the shape to be different than the printing paper? You either have to crop the image or print with a wider border on one side... the proverbial round peg in a square whole.. Or the not so proverbial "one shaped rectangle into another shaped rectangle whole".

Well here's a solution... set the aspect ratio of the final print during the scanning process!
Most scanning software provide a way to "lock" the input setting for a fixed size... this is good - very good and necessary for this tip to work. Set the aspect ratio of your final print size [width / height] into the "input"of your scanning software... [an 8x10 would be "4x5" or "1.0x0.8"]. Now "lock" this size. Then, as you drag the bounding box, it will get larger or smaller while the aspect ratio... ("the shape" of the box and your final print) is maintained. When you have the desired composition, simply set the final print size and resolution desired [Method 3] or enter the pixels output needed [Method 4] and let the scanning software do the rest (adjust the scaling). You will have a file with the proper resolution and shape to print!

Activity... Understanding "File Resolution"
This activity requires scanning software with the ability to enter INPUT, SCALING and OUTPUT settings.
This activity is intended to demonstrate that "File Resolution" is determined at the time of scanning. Photoshop just takes this "File Resolution" (pixels) and redistributes (or reshapes) that resolution. If Photoshop's "Resample Image" is unchecked, then Photoshop changes the "File Resolution" by discarding or creating ugh! pixels.
For this test, scan in "grayscale" mode.
1 - Set scan resolution to 300dpi and scaling at 100%
2 - With "bounding box" (or by entering values), select an area to scan of 5" width and 4" height
3 - Scan
4 - Without changing the bounding box, change the scan resolution to 100dpi and scaling at 300%:
5 - Scan
6 - View both files in Photoshop [Image>Image Size] and observe:
  - just as we scanned:
a) the 1st scan has a Print Size width of 5", height of 4" and "print" resolution of 300pixels/inch
b) the 2nd scan has a Print Size width of 15", height of 12" and "print" resolution of 100pixels/inch
- however both scans have the same "File Resolution":
c) width = 1500 pixels; height = 1200 pixels and 1.7MB file size
- change output print size:
d) with "Resample Image" unchecked, change "print" resolution of both scans to 150pixels/inch and notice the Print Size of each changes to a width of 10" a height of 8"
Conclusion:
  1) Total pixels acquired during scan determine "File Resolution"
2) with "Resample Image" unchecked, Photoshop redistributes the "File Resolution"
3) with "Resample Image" checked, Photoshop changes the "File Resolution"