Resolution question regarding canvas/print?

TJ
Posted By
Tyler_Jameson
Sep 27, 2008
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851
Replies
15
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Closed
If I make the resolution of a photoshop document canvas 300 PPI (pixels per inch), will it still print out at the original dimensions I set the canvas to? I am asking because I tried a target canvas size of 594mm width by 841mm height on two separate photoshop documents, one at 300 PPI and the other at 72 PPI and it resulted in a huge size difference between the two documents targeted at the same image size. I want to know if they will print at 594mm x 841mm regardless of resolution.
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S
Silkrooster
Sep 27, 2008
For that to happen you will have to enable resampling. Think of the ppi as a multiplication factor. To have the image print at the same size at 300 ppi as it does with 72 ppi the number of pixels wide and high will have to be changed or resampled.
Therefore it is important that your image should start with the 300 ppi and resample down to 72 ppi and not the reverse. It is easier to remove pixels then it is to add non existing ones.
Hope this helps.
TJ
Tyler_Jameson
Sep 27, 2008
If I start a new ps file and the canvas is 500 x 500px at X PPI, will it print at 500 x 500px? X being the variable. It shouldnt matter what the PPI is right?

NOTE: It should print out the same size, but different PPI shows a huge difference on my computer. But I’m guessing the reason for that is because monitors can only output certain resolutions and use DPI instead, so they can’t possibly show you a high resolution of 300 pixels per inch. But all in all, a size 500 x 500px document, whether it is 72 or 300 PPI, should print out as 500 x 500px right?
F
Freeagent
Sep 27, 2008
Stop. Make a U-turn and go back…

Inside Photoshop, the image exists as pixels. That’s all that counts: A small image is few pixels, a big image is many pixels.

The concept of resolution has no meaning at this point.

OK, so far so good. Now you want to print out that image. This introduces a new variable: How big should those pixels appear on paper? In other words, how many pixels per inch? That’s a fair question, and one that you, the user, must provide the answer to.

But none of this affects the basic fact that the image is x by y pixels in size.

But here’s the catch: in an effort to simplify the workflow the PS engineers threw in a secondary function in the Image Size dialog. It’s called "Resample Image" and it’s an exploding device if you’re not fully aware of what it does. Keep it unchecked at all times, unless you’re braced for it…this little box will change the actual file size, destructively, not just the way it prints out.
F
Freeagent
Sep 27, 2008
A Feature Request that will never happen:

Separate the two. Remove "Resample Image" from the Image Size dialog, and put it under File as "File Size".
JW
John_Waller
Sep 27, 2008
If I start a new ps file and the canvas is 500 x 500px at X PPI, will it print at 500 x 500px? X being the variable. It shouldnt matter what the PPI is right?

Avoid confusing terms.

It won’t "print at 500 x 500px". It’ll "print 500×500 px @ a specified resolution to give an image of dimensions = w x h". The resolution will determine your document size and image quality.

The important factors are your original image size (pixel dimensions) and your target output (website, offset printing or something in between).

Pixels are your ingredients. Document size and resolution determines how you print those ingredients (image size & quality).

Uncheck "Resolution" in the Image Size dialogue and you can set whatever document size you wish.

Print quality will vary drastically though. Good @ 300 dpi. Poor @ 72 dpi.

But I’m guessing the reason for that is because monitors can only output certain resolutions and use DPI instead, so they can’t possibly show you a high resolution of 300 pixels per inch.

Monitors don’t care about DPI (or image resolution).
They only care about image dimensions measured in pixels since 1 image pixel = 1 screen pixel.
The same image looks the same @ 72 dpi or 300 dpi
See http://www.leannehoad.com.au/temp/dpi_test.htm

But all in all, a size 500 x 500px document, whether it is 72 or 300 PPI, should print out as 500 x 500px right?

500 x 500 px means you’ve got 250,000 pixels to print. No more, no less (without resampling). Resolution determines how many pixels are crammed into how much space i.e. document size and quality.

500 x 500px will print at different sizes subject to resolution. Low res = big print size, low quality unless it’s small enough that it doesn’t matter e.g. postage stamp size.
Hi res = smaller print size (more pixels per inch PPI), high quality

—
Regards

John Waller
TJ
Tyler_Jameson
Sep 27, 2008
Okay I’ll get straight to the point. I need to make a poster that is 594mm x 841mm and I want to do the resolution at 300 PPI. I notice the poster looks way bigger in photoshop when compared to a 72PPI version. Will this 300 PPI poster still print out at 594mm x 841mm?
F
Freeagent
Sep 27, 2008
Okay I’ll get straight to the point

Fair enough, it was just that you didn’t seem to fully grasp the basics of the image size dialog.

Short answer: If your image size dialog looks like this

< http://www.pixentral.com/show.php?picture=1QpooSglBc71vcxJln mywqQHBtR4JX>

then yes. Notice the rounding off errors as millimeters don’t go evenly up in pixels per inch.
TJ
Tyler_Jameson
Sep 27, 2008
You know what’s weird, when I make a picture 300 PPI and then make the canvas from the image the size it needs to be (594 x 841mm), it isn’t that huge.

But when I start a new file and it gives me options and I set the document to 300 PPI (not the image), and THEN put the 300 PPI image in the new project window the size of the canvas is way bigger.
F
Freeagent
Sep 27, 2008
This makes no sense. A canvas of 594 mm x 841 mm @ 300 ppi is the same no matter which way you make it. If it isn’t, you must be changing something along the way. How do you

make the canvas from the image

by the way? I assume you use "Canvas Size", as you should.

In any case – just to clear all doubt – make sure, absolutely sure, you don’t have "resample image" checked in the Image Size dialog.

BTW, if you paste an image in Photoshop, the original resolution of that image is irrelevant. It goes by pixel count to the canvas at it’s resolution.
F
Freeagent
Sep 27, 2008
Wait a minute. Just trying to figure out what you’re saying here…

it isn’t that huge.

Are you talking about screen size? If so, that simply doesn’t matter. Forget it.
JJ
John Joslin
Sep 27, 2008
Beat me to it! I was going to say look at the % magnification.
F
Freeagent
Sep 27, 2008
Beat me to it!

Well, now you know how that feels. Usually it’s been the other way round 😉
TJ
Tyler_Jameson
Sep 27, 2008
So how should I begin my poster. should i start a new document and set the canvas to 549 x 841mm and the PPI to 300, and THEN add the images?
DM
dave_milbut
Sep 27, 2008
if it’s not a big deal, it’s best to work at the right resolution from the start, imo.
JW
John_Waller
Sep 28, 2008
So how should I begin my poster. should i start a new document and set the canvas to 549 x 841mm and the PPI to 300, and THEN add the images?

Ideally, yes.

—
Regards

John Waller

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