• Nara

On Print size and DPI

Quite often, we get a question

"Why you insist on 300dpi resolution for the print?"


This blog tries to answer the above.

However this blog doesn't provide best practices for preparing the image for the print.We cover this in some other post.


Before answering this question, we need to understand the term “Resolution “.


Let us broadly define it.


Resolution is an indication of the level of details rendered on a media, with media can be a laptop screen or a computer monitor or a print.

Higher the resolution, more the details are rendered.

In the context of print, resolution is defined in DPI - Dots per Inch


A 96 DPI resolution has more details than 72 DPI

A 150 DPI resolution has more details than 96 DPI

A 300 DPI resolution has more details than 150 DPI


So what a 9000 x 6000 pixel image mean for a print?

It just means the image has 9000 pixel on horizontal side and 6000 pixel on vertical.Otherwise it doesn’t tell how it would get rendered in the print .


This 9000x6000 pixel can be printed with 300 or 150 or 72dpi resolution.With different resolutions, the print output changes with respect to size and details.


Perhaps,we have to understand the relationship between resolution,print size and viewing distance .


BTW,do you know at what resolution the bill boards are printed?


As small as 10 DPI.Given that

that bill boards are seen over a long distance,from highways kind, this low resolution is sufficient enough to print the image in such huge size.


So here comes the viewing distance factor.

Closer the viewing distance, higher details are needed (hence higher resolution).

Assuming you want to print an image of 9000x6000 pixels, table gives the relationship between the three:


As you can see, at 30dpi, you can print 300x200inches in size, but you need to view the picture only at 20ft or more.


Here is a more general guideline between resolution and distance:



In other words, if you are printing at 10dpi, unless you see from 60ft or more, you will not be able to see the details.A closer distance will create a pixelated or soft feel.


So when an image can be printed at 72 dpi, why you insist for 300 dpi resolution ?



If you are able to force the viewer to see the print at 8ft distance, then printing at 72 dpi is not a problem.The viewer would be able to appreciate the art. However, most of us tend to see the image at much closer distance.The closer viewing brings artifacts of the photo like blur,pixelation,noise etc as well getting softer, thereby under-appreciating the art work.Hence it is always suggested to go for 300 dpi.


Having touched upon DPI and viewing distance relationship, we also need to understand the aesthetic connection as well.

In order to appreciate an image, one should see the photograph in full. The complete view of an image depends upon the viewing distance.As a guideline,if you are between 1.5 to 2 times of the Diagonal length of the image, the view will be pleasing.


However, this distance is not related to resolution, but the aesthetics.

Here is the table between print size and optimal viewing distance:



Conclusions:

In case you are able to enforce the optimal distance viewing for your prints, you can compromise for the low resolution prints. Most of the time,it is not indeed the case.Both Photographers and general public would love to investigate the work at closer distance sometimes even touch the prints to get the feel.The low resolution prints should not be a hindrance of the experience or a denial of enjoyment due to pixelation or softness. Hence it is recommended to abide by 300dpi as your default resolution for the printing.


Post Script : There are few other factors like paper type,image characteristics like low-contrast impacts the choice of resolution.We cover them in another blog.


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Note : Calculation of pixel size for a given print size .

Pixel Count = Print size in inches X DPI.

For a 30 X 20 inch print size :

Horizontal Pixel = 30 inch X 300 pixels per inch = 9000 pixels.

Horizontal Pixel = 20 inch X 300 pixels per inch = 6000 pixels.

Pixel size = 9000 X 6000


For a 18 X 12 inch print size :

Horizontal Pixel = 18 inch X 300 pixels per inch = 5400 pixels.

Horizontal Pixel = 12 inch X 300 pixels per inch = 3600 pixels.

Pixel Size = 5400 X 3600


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