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Help needed with sizing in p-shop

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  #1  
Old 11-22-2011, 09:52 PM
photogdude photogdude is offline
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Help needed with sizing in p-shop

it's kinda technical.

i need to print an 8x10 and 4x6 of some images at what the image is at a 100 Percent zoom level.

it has to be fairly accurate

whats the math to do that?

i can't post examples, cause of privacy, I'm hope i explained it ok

any help will be greatly appreciated.
thanks
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  #2  
Old 11-23-2011, 08:07 AM
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Chain Chain is offline
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Re: Help needed with sizing in p-shop

I'm not sure exactly what you are asking... It's rather vague. I will just make sure then to cover everything...

The zoom percentage you see on screen has nothing to do with print. When you view it at 100 % it simply means that one pixel in the image = one pixel on the screen. How big is would be in centimeter/inches depends on your monitor (use a ruler).

An image is made up of pixels (the small squares you see if you zoom in beyond 100%). And the size of an image is then naturally measured as pixels. For example 3000x2000px.
An image has no "true" physical print size.

When we print it we choose how big we want it. The bigger we want it printed, the bigger the pixels will be. Here we use the term "Pixels per inch" (PPI) to describe how many pixels we want squeezed into an inch (and thus how large they are). It is often also referred to using the less accurate term "DPI" (dots per inch).

300 ppi is considered high resolution and good for prints that should be studied up close; photos, magazines, etc.
A large poster might have a lot lower ppi, but the viewer is further away, so it's fine.
Lower ppi == lower quality (it will look blurry and/or pixellated).

A typical computer monitor might be around 100 ppi (varies a lot). That is why images need to be larger (more pixels) on print than on screen (if they are to be printed at 300 ppi and viewed at the same size).

So let's say the 3000 px wide image is to be printed at 300 ppi. Then then it will be 10 inches wide. You can do this calculation the other way as well: If you want an image to be 10 inches wide then it needs to be at least 3000 px if you want 300 ppi.

px/in=ppi.

Now, that was the theory. Over to Photoshop.


In Photoshop you manage/change the size of an image through Image > Image Size...
(Check "Constrain Proportions" to avoid stretching the image.)
Uncheck the "Resample image" checkbox. This prevents the pixels from changing (this will reduce quality, so you want to avoid it unless you really need it).
You can now change the print size by either changing the size in cm/inches or choosing the resolution (ppi) you want (Tip: this can be overridden from the Print window as well).

So, if you have an image in Photoshop, and you want it to be 8 inches wide when printing, just type in 8 inches in the "width" box. The heigth and ppi will change accordingly.

If the proportions of your image is wrong you'd want to crop it. Choose the crop tool from the tools panel. A good tip here is that if you know the size you want it to be, just fill it in the fields on the top bar. This will resize the image for you.

The ppi of your monitor:
If you want to know the resolution (ppi) of your monitor first find how many pixels wide your screen is (horizontal resolution). You can find this number under your display settings.
Mine is 1920 px wide. Then divide this by the width of the monitor's visible area (measure using a ruler – mine is ~19,2 inches).

So the formula is px/in=ppi.
That gives me 1920/19,2=100ppi.

(As this formula goes both ways I now know that a 300 px wide image is displayed 3 inches wide on my screen).
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File Type: png Screen shot 2011-11-23 at 15.10.12.png (28.1 KB, 5 views)

Last edited by Chain; 11-23-2011 at 08:12 AM.
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  #3  
Old 11-23-2011, 01:44 PM
photogdude photogdude is offline
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Re: Help needed with sizing in p-shop

thanks for your reply,
let me re-ask the question

lets say i print a 1"x1" print of a 1" ruler with little 2mm circles, now lets say i take that 1x1 and enlarge it to 20x20, so now in front of me i have a 20"x20" photo of a 1" ruler with 2mm circles, but of course the actual size of the circles are now 40mm. now i cut that 20x20 with a pair of scissors to 8x10. the size of the circles hasn't changed.

so now i basically have an 8x10 photo of a 2mm circle that has been magnified 20x

thats what i'm trying to do in photoshop.

hope that explains it better

thanks
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Old 11-23-2011, 04:38 PM
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Chain Chain is offline
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Re: Help needed with sizing in p-shop

Quote:
Originally Posted by photogdude View Post
thanks for your reply,
let me re-ask the question

lets say i print a 1"x1" print of a 1" ruler with little 2mm circles, now lets say i take that 1x1 and enlarge it to 20x20, so now in front of me i have a 20"x20" photo of a 1" ruler with 2mm circles, but of course the actual size of the circles are now 40mm. now i cut that 20x20 with a pair of scissors to 8x10. the size of the circles hasn't changed.

so now i basically have an 8x10 photo of a 2mm circle that has been magnified 20x

thats what i'm trying to do in photoshop.

hope that explains it better

thanks
So, you want to simply make it 20x the size? Then go to image size and type in the size you want (2000%). If it sais 1in change it to 20in. Keep in mind what i said in the previous post.

If you want to crop/cut away a specific amount (say remove the top half), you can use the crop tool as i said and fill in the values. You can also use image - canvas size...
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Old 11-23-2011, 04:42 PM
photogdude photogdude is offline
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Re: Help needed with sizing in p-shop

nope, i'm not communicating it properly, but thats ok, i think i figured out what i need to do

thanks
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