# Minimum DPI for printing?



## schumionbike

Hey everyone, I was wondering what the minimum dpi that you would print at if you have a fairly sharp image?  I know most printer say that a minimum should be 100dpi but that seem quite low, anyone ever try it?  I recently print an 11x14 from a 7 megapixel camera which would give it 212 dpi.  The picture came out very well, not complaint from me.  I wonder if I can print it at 16x20 safely which would give it around 150 dpi.


----------



## RVsForFun

...what your dpi is. The printer will convert whatever dpi file you send to a good printed image. I regularly send 72dpi files from my 8mp camera for 20x30s and they come back flawless.


----------



## Garbz

Use the right terminology. DPI is the number of dots a printer lays down per inch. This should be high. Really high. Even cheap printers print at 2400dpi these days.

You are talking about PPI. You have shown a very clear point. 72ppi is horrible when sent to the printer. Most likely wherever you are sending them to may be upsampling the resolution. 

The standard for lab work is 300ppi, I believe this is a resolution where at arms length a person with perfect vision can no longer distinguish individual pixels. I suggest always print in 300ppi. If the image is smaller than resize it in photoshop or some more advanced filtering program, something with a windowed filter like Lanzcos. If you send a low-res picture to a printer no interpolation will be done and it looks worse than basic resizing in photoshop.

Anyway 150ppi should be acceptable too.


----------



## astrostu

300 ppi is standard.  It's what I print at when I can.  When you sell photographs (w00t ... my first one just this past weekend!), "high resolution" is 300 ppi at whatever size they need.

But, most people don't know this (it seems) and tend to print their stuff at much lower resolution.  I believe that Costco recommends no lower than like 115 ppi before they give you a warning.

I've printed at 150 ppi and I can see pixelation in the final result.

However, when I make posters for science conferences, I use 144 ppi ... but on a poster printer and glancing at the poster from several feet away, this is fine.


----------



## schumionbike

Thanks guys, I'm still a little confuse on DPI and PPI bussiness but I understand the end result:mrgreen:.  So 150 DPI/PPI shouldn't be too bad.  Cool, thanks everyone.

astrostu: congrat on selling your first image.  I sold my first one to my....dad,lol, the 11x14, now he kinda want a bigger one.


----------



## astrostu

schumionbike said:


> Thanks guys, I'm still a little confuse on DPI and PPI bussiness



On the computer screen, everything is _normally_ displayed at 72 pixels per inch.  In recent years, this has changed as monitors got better and resolution independence was introduced.

So if you have an image in PhotoShop and it's 4"x6" at 72 pixels per inch, it will be exactly the same size on the screen as a 2"x3" image at 144 pixels per inch.  It will have just as many pixels in the image.

However, when you go to print, one will come out at 4"x6" and the other will come out at 2"x3".  Any modern printer can lay down a couple thousand dots per inch, so technically you could have real information about the photograph every 1/[few thousand] inches.  But, your eye can't tell the difference between having information at 1/[few thousand] inches vs. 1/[few hundred] inches.  Hence, it is not necessary to have in the original image as many pixels per inch as the  maximum dots per inch on the printer.

If you were to print the afore-mentioned 4"x6" at 72 pixels per inch, then you would be able to pick out with your eye the individual pixels in the printed image because for a block of the image that's 1/72"x1/72", it should all be the exact same color (this is about 0.35x0.35 mm, so it's pretty small, but you can definitely tell).

That's why people recommend printing at higher pixels per inch, so that you have smaller "boxes" of information on the final print.  Whether or not you can see the pixelation depends upon your own eyesight.

I hope that helps explain the difference!


----------



## schumionbike

thanks for the detail explaination, I understand it now.  Thanks for all the info.


----------

