Choosing the Correct Scanning Resolution

At which resolution should we scan a photograph to get the best print quality on an Ink Jet Printer?
 
Since the required image resolution is highly dependent on the type of output you choose for presenting your work, it is best to define your requirements before scanning. This will avoid your image data being too big and will also make sure your resolution is not too low. It may however mean that at a later stage, when another job comes with different requirements, you will have to scan and process again.
 
In cases where you know you will apply a couple of changes to the original, it is wise to make a larger scan, make all the changes you wish and in addition to the larger file you will keep in storage make another that is just right for your chosen type of output. This way you will not reduce the print time due to a large amount of "unnecessary" data while at the same time keeping all options open.
 
In order to find the correct scan resolution for your job, you can either use the utilities included in your scan program or use the following tips:
 
The ideal image resolution range is from 250 to 300 dpi for an Ink Jet Photo printer.
 
250/300 dpi is the best resolution for a 8 x 10 photo where the viewer distance is very close. In the case of a larger photo, we usually assume that the viewing distance is equal to the document size. This allows the image resolution to be smaller, which makes the data file smaller. For example, for a 24 X 36 cm photo, 200 dpi image resolution is acceptable.
 
Image resolution must also be modified according  to the size of the original. In most cases, the original will be enlarged. You can easily find out the correct scanning resolution by applying the following formulas :
 

1. (Size of output ) / (Size of original ) = (Enlargement factor)
2. (Enlargement factor) x (Image resolution) = (Scan resolution)
 
Please note that the image resolution is not the printer resolution itself. This is because of the way images are formed by drop-on-demand inkjet printers, like EPSON Stylus printers. Here in principal one pixel can only be either Cyan, Magenta, Yellow or Black or any other color that is ejected out of the nozzle of your printer. The color is than mixed by the eye. In your data one pixel can be already the mixed color and contains therefore more data. For this reason the resolution you need for your files is far lower than the resolution your printer needs for supreme output.
 

 

The tables below offer a detailed practical explanation of the above:
 
Printing photo = < 8 x 10
Ideal image resolution = 250 300 dpi
 
Source Output size Scan resolution
36 mm negative / positive (135) 4 X 6 1000 - 1200 dpi
36 mm negative / positive (135) 8 X 10 2200 - 2700 dpi
4 X 5 inch posi 4 X 6 250 - 300 dpi
4 X 5 inch posi 8 X 10 500 - 600 dpi
4 X 6 Photo 4 X 6 250 - 300 dpi
4 X 6 Photo 8 X 10 500 - 600 dpi
8 x 10 Photo 4 X 6 125 - 150 dpi
8 x 10 Photo 8 X 10 250 - 300 dpi
 
Printing photo = < 24 x 36
Ideal image resolution = 200 dpi
 
Source Output size Scan resolution
36 mm negative / positive (135) 11 X 14 2400 dpi
36 mm negative / positive (135) 16 x 20 3600 dpi
36 mm negative / positive (135) 24 x 36 4800 dpi
4 X 5 inch posi 11 X 14 500 dpi
4 X 5 inch posi 16 x 20 750 dpi
4 X 5 inch posi 24 x 36 1000 dpi
4 X 6 Photo 11 X 14 500 dpi
4 X 6 Photo 16 x 20 750 dpi
4 X 6 Photo 24 x 36 1000 dpi
8 x 10 Photo 11 X 14 300 dpi
8 x 10 Photo 16 x 20 400 dpi
8 x 10 Photo 24 x 36 600 dpi
 
Printing photo = < 40 x 60
Ideal image resolution = 150 dpi
 
Source Output size Scan resolution
36 mm negative / positive (135) 36 X 48 5500 dpi
36 mm negative / positive (135) 40 x 60 6750 dpi
4 X 5 inch posi 36 X 48 1000 dpi
4 X 5 inch posi 40 x 60 1500 dpi
4 X 6 Photo 36 X 48 1000 dpi
4 X 6 Photo 40 x 60 1500 dpi
8 x 10 Photo 36 X 48 600 dpi
8 x 10 Photo 40 x 60 750 dpi