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Damn DPI printing shiz
show user profile  9krausec
I know this isn't a 2d printing forum, but I need some help.

I sort of know what DPI is... 72 for screen, 300 for print and 20-30 dpi for billboard... Cool.

Now my output renders at a standard of 72dpi, cool...

How do I find out what resolution I need to render to print things at certain sizes (let's say 42 inches) at 300 dpi? Is there any recommended calculator on the web that you guys use? What is the appropriate way to do this in PS?

I can make a test document at however many inches by however many inches at 300 dpi, but how do I accurately translate that to 72 dpi to find appropriate pixel resolution? I hate print, she's a harsh mistress.

Thanks for the help guys, this is confusing for me right now as I do not deal with print at all (until now).

- Portfolio-

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10/6/2015 1:25:13 AM (last edit: 10/6/2015 1:25:13 AM)
show user profile  Nik Clark
42 inches @ 300 dpi

42 * 300 = 12600 pixels

DPI doesn't really mean anything except in a physical print.

If you create a 42 inch by 42 inch Photostop document at 300 dpi, choosing Image Size you will see how many pixels your document is. the 42 x42 inch document would be 12600 x 12600 when set to 300 dpi.

Just work out the pixels you need and use that.

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read 530 times
10/6/2015 1:50:03 AM (last edit: 10/6/2015 1:51:15 AM)
show user profile  S. Silard
DPI = Dots Per Inch, thus it's equal to Pixel Per Inch. Pretty obvious...

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read 523 times
10/6/2015 2:00:46 AM (last edit: 10/6/2015 2:00:46 AM)
show user profile  9krausec
Thanks for the help guys. I think I have it figured out (hopefully)

- Portfolio-

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10/6/2015 2:44:27 AM (last edit: 10/6/2015 2:44:27 AM)
show user profile  9krausec
Okay, so this is what I've gathered from this thread and banging my head against the wall for a while..

A pixel is a pixel (thanks RedStar for that advice). A pixel is a pixel as in not the pixels on your screen, but pixels that make up an image.

So if I have a 6000 x 6000 pixel image (so PPI in this instance referring to the pixel count that the image is made up of), it doesn't matter if the digital image is 300 dpi (ppi) or 72 dpi (ppi), it's still 6000 x 6000 pixels... The DPI is how many pixels get printed per that inch.

If I render something out the default dpi (ppi) stored in that image is 72. That can be changed to 300 in PS. My pixel count should not change, just how it's going to be printed.

Sound about right? I know this is probably very basic for some of you, but I've only ever had to worry about stuff viewed on screen. I'm familiar with 72 dpi (ppi) and resolution (1920x1080 and so forth) along with frame rate.. Film stuff. Not print stuff.

- Portfolio-

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10/6/2015 3:05:12 PM (last edit: 10/6/2015 3:05:12 PM)
show user profile  STRAT
pretty bob on.

yes, dpi/ppi is a physical thing. you can have a 3000x3000 pixel image at both 300 dpi or 72 dpi.

generally, your pixel render size at render time should be determined by what your image will be ultimately used for. if its for print then calculate the physical size in inches by 300. this is the print standard. if it's for poster size, establish from the printing guys what printing facilities they use. if its for web then 2-3k renders are generally fine. again, same for all the different tv ressys.

dont worry over it mate.


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10/6/2015 4:08:26 PM (last edit: 10/6/2015 4:11:16 PM)
show user profile  9krausec
Thanks Strat. The application is going to be for magazine, billboards and banners. I'm thinking 6k should be plenty.

- Portfolio-

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10/6/2015 4:12:48 PM (last edit: 10/6/2015 4:12:48 PM)
show user profile  STRAT
for up to A3 print 6000 pixels is fine. more than needed. for banners and posters i'd ask the fine size needed (physical size). if we're unsure we'll generally render about 9K pixels. but this is usually overkill. you'll fine 6000 is generally fine for that too


read 459 times
10/6/2015 4:15:58 PM (last edit: 10/6/2015 4:16:25 PM)
show user profile  chillywilson
No no!

If you take a 72dpi of HD into PS and you need 300, with resample image on, your pixel count will go up to 8000x4500, not your inches.

The loss of quality will happen.

For print start with the inches and the dpi that you need, that will tell you how many pixels is need for a render or image.

Like Nik was saying 42 inches is 12600 across, 42 inches at 72 dpi is 3024 across.

Render your image at 12600
Open in photoshop turn off all the resize then change your dpi to 300.

You'll notice that you inches will go from 175 inches down to 42.

{eidt: I was writing this when the others came in.}

read 455 times
10/6/2015 4:30:31 PM (last edit: 10/6/2015 4:31:46 PM)
show user profile  STRAT

golden rule always - render to size at the offset. NEVER size up in post. Never. Sizing down is ok, but never up. just changing up the DPI value in post isnt the correct method at all. but I'm sure you know this already.


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10/6/2015 4:44:15 PM (last edit: 10/6/2015 4:44:15 PM)
show user profile  9krausec
@Chillywilson - Alright. Does the explanation which I described above hold true if resample image is off? That's what I was figuring when I wrote that. Resampling the image will affect the image quality which I'm not looking to do. Thanks for the reply.

- Portfolio-

read 439 times
10/6/2015 4:45:35 PM (last edit: 10/6/2015 4:45:35 PM)
show user profile  chillywilson
Yes resampling up always losses quality, sampling down will not.

When I'm in a pinch and a client wants a size up without waiting for a render, I go from 72 to 150 to 250 and send hoping that will be ok.

I never go from 72-300 but resize in steps if necessary.
Also use Bicubic Smoother in the resample image drop down.

But again only if I really need to scale up, most people will wait a day for the render.
read 435 times
10/6/2015 4:50:12 PM (last edit: 10/6/2015 4:50:12 PM)
show user profile  9krausec
Alright. So I'm going to beat this dead horse (thank you for your patience). Are the below fundamentals correct? The top instructions are given for billboard printing.

The second image shows the document setup to the appropriate specifications. The bottom image shows the document dimensions changed to reflect the actual bulletin size (14' x 48').

The DPI changes to 12.674. So would it be correct to infer that the billboard itself will be printed along the lines of 12-13 dpi? Sorry again for the continual chatter on this. I just want to make sure absolutely that I'm getting this straight.

- Portfolio-

read 423 times
10/6/2015 7:23:30 PM (last edit: 10/6/2015 7:23:30 PM)
show user profile  9krausec
Just called the billboard company, haha. Got it all figured out. The logic was correct. End of thread (hopefully).


- Portfolio-

read 418 times
10/6/2015 8:06:29 PM (last edit: 10/6/2015 8:06:29 PM)
show user profile  chillywilson
Damn it I was just about to make your thing for you.

When I was making movie billboards different factors when into because of difference in printers.

Usually the printer will give you the formula some bill companies say 1 foot equals 1200pixels at 12 dpi.

Others will they want 6 in x 4 in at 240dpi.

read 415 times
10/6/2015 8:11:58 PM (last edit: 10/6/2015 8:11:58 PM)
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