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A guide to resolution and print size

J. Ramon Palacios (jrp)

Keywords: storing, processing, printing, guides, tips

ppi and dpi

You are now the proud owner of both a film scanner or a digital camera and an inkjet printer. But may have wondered what is the best resolution -or pixel density- of a digitized image to allow for the production of a good print in a given size.

Building blocks of a digital darkroom

A printer's software translates pixels into ink dots, that's why printer's resolutions are expressed in dpi, dots per inch. How many dots per inch is a printer capable of producing on paper is a measure of its quality. In general, the more dpi, the smoother is the tonal gradation in the print, the finer the definition and the wider the color gamut.

On the other hand, a digital image from a scanner should be stated in ppi or pixels per inch. For example, specs for my Nikon CoolScan IV ED LS-40 state it is a 2900dpi scanner. Looking into the effective reading resolution with the MA-20 adapter for slides, clearance of 25.1 x 36.8mm, the scanner yields images 2,870 x 4,203 pixels in size, or 12Mpixels. Roughly the equivalent to a 6Mpixels digital camera image, as it seems from experience. 

Doing calculations in the width side: 2870pixels/25.1mm = 114.3426 pixels per mm or 114.3426 pixels per mm x 25.4mm per inch = 2904 pixels per inch, approximately 2900ppi.

Calculations on the length side of the image scanned, reach the same result (4203pixelsx25.4mm per inch/36.8mm=2901ppi, pixels per inch).

So it is ppi, not dpi. This seems to be a common (translation?) mistake. My flatbed Epson scanner also talks about dpi when it should be ppi. Minolta, Hewlett Packard and other brand scanners they all make the same misuse of the term. Strange.

A CoolScan 4000 ED will yield 3,946 x 5,782 pixels from a 35mm negative or unmounted slide, or 22.8Mpixels, roughly the equivalent to a 11.4Mpixel digital camera image.

Digital images sizes from digital cameras are also stated in pixels, like VGA, 640x480.


Minimum resolution for magazine-quality printing is 300ppi, so a VGA image of 640x480 will only allow for a decent print of 3.2 x 1.6 inches (640pixels/300ppi=2.1 inches by 480pixels/300ppi=1.6 inches). 640x480=0.3Mpixels.

If you want to make a good 8x10 print under the above standards, it will be best to have a 300ppi image with a size of 2400 by 3000 (8x300 by 10x300), a 7.2Mpixel scan. So now you know exactly the why of the quest for higher Mpixel rating from scanners (and digital cameras), even when interpolation may acceptably invent pixels where there are none. 


Granting that good prints can be made with good printers at 200ppi (for example with dye sublimation printers), with inkjet is better to make them at 300ppi. Below a reference table to answer the above recurrent question in the forums.

Building blocks of a digital darkroom


Image size in Pixels
(Virtual Size of scanned film Images)


Uncropped print size (inches) at 200ppi

Uncropped print size (inches) at 300ppi


640  x  480


3.2 x 2.4

2.1 x 1.6

1,024 x 768


5.1 x 3.8

3.4 x 2.5

1,280 x 960


6.4 x 4.8

4.2 x 3.2

1,504 x 1,000 1.5 7.5 x 5.0 5.0 x 3.3

1,632 x 1,224

2.0 8.2 x 6.1 5.4 x 4.1
2,000 x 1,312 2.6 10.0 x 6.6 6.7 x 4.4
2,240 x 1,488 3.3 11.2 x 7.4 7.5 x 5.0
2,275 x 1,520 3.5 11.4 x 7.6 7.6 x 5.1
2,272 x 1,704 3.9 11.4 x 8.5 7.6 x 5.7
2,590 x 1,920 5.0 13.0 x 9.6 8.6 x 6.4

3,008 x 2,000


15.0 x 10.0

10.0 x 6.7

4,256 x 2,848

12.1 21.3 x 14.2 14.2 x 9.5
4,536 x 3,024 13.7 22.7 x 15.1 15.1 x 10.1
5,782 x 3,946 22.8  28.9 x 19.7 19.3 x 13.2

The data above is conclusive for inkjet printers. It could appear controversial for professional printers, -even if they are talking about digital camera output- as they seem able to handle lower definitions; for example, Kodak seems able to handle lower ppi, unless they are taking about digital camera images, when it recommends as below: 


"For a 4" x 6" print, the image resolution should be 640 x 480 pixels minimum"
That represents 120ppi at best (480pixels/4 inches) on one axis, 106.6 in the other.

"For a 5" x 7" print, the image resolution should be 1024 x 768 pixels minimum"
So resolution increases to 146.3ppi (1024/7), 153.6ppi in the other axis.  

"For an 8" x 10" print, the image resolution should be 1536 x 1024 pixels minimum"
That is 153ppi (153.6/10) and 128ppi (1024/8).

But then it drops drastically: "For a 16" x 20" print, the image resolution should be 1600 x 1200 pixels minimum"
80ppi (1600/20) and 75ppi (1200/16).

And even lower for a larger size print: "For a 20" x 30" print, the image resolution should be 1600 x 1200 pixels minimum"
53.3ppi (1600/30) and 60ppi (1200/20).


In any event, you'll be safer by following the table above.


Pro labs will rather work with 300ppi resolution images. But the resulting print sizes from scans or digital camera images in the table in the preceeding page are not standard. What to do? Below the optimal sizes of images.

Building blocks of a digital darkroom


Image size in Pixels
(Virtual Size of Image)


Print size (inches)
at 300ppi

1,050 x 1,500 1.575 3.5 x 5
1,200 x 1,800 2.160 4 x 6
1,500 x 2,100 3.150 5 x 7
1,800 x 2,400 4.320 6 x 8
1,800 x 2,550 4.590 6 x 8.5
2,400 x 3,000 7.200 8 x 10

2,400 x 3,600


8 x 12

3,300 x 4,200

13.860 11 x 14
4,800 x 6,000 28.800 16 x 20
6,000 x 7,200 43.200 20 x 24
This means you have to crop your images to conform to these pixel dimensions and maybe resize them (Bicubic resampling, constraining proportions) if too big or a little too small for a standard print size. An image editor is of course required; Photoshop is the photo industry standard.

For a fast workflow when dealing with several images this is what I do:

I. File > New - Assigning it a standard size, lets say 1,500 x 2,100 pixels at 300ppi for a 5x7 inches vertical print.

Notice this is a 9 Mpixels image size. If your digital camera has 6 Mpixels, don't worry, remember the table is for scanned film images where half of that is spent on grain. So for a 9 Mpixels images you need in theory just half or 4.5 Mpixels, but the closer you are to 9 (in this case), the better; of course.




II. File > Open - Your file. Check its proportions.

(I have a 29Mpixels image because that's the resolution of my scanner)

III. Resize image and crop if needed as close as possible to the size of the New file.

IV. Copy and paste the resized image on top of the New file. And that's that, just remember to flaten layers and rename the file before saving.

There are other ways to do this of course and for really large volume you can always resort to the:
File > Automate > Batch


Have a great time!

(3 Votes )

Originally written on December 10, 2005

Last updated on May 3, 2018

J. Ramon Palacios J. Ramon Palacios (jrp)

JRP is one of the co-founders, has in-depth knowledge in various areas. Awarded for his contributions for the Resources

San Pedro Garza García, Mexico
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