Printing resolution and PPI - have I got it right?

Will James

Will James

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Will
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Hi,

I want to keep this short as I could write loads about this, so here goes:

A client has said he would like to buy one of my photos - he says he wants a full-res image and he will print it on 7x5" photo paper.

To provide him with the best quality, do I:

a) Resize the original image (3840 x 2065) to 7x5" in Photoshop, giving 549ppi,

OR

b) Resize the original image based on 300ppi in Photoshop, thus giving him a 12.8 x 6.9 inch image, of which he will have to resize to print on 7"x5", but he has an option of printing larger?



I've just read up lots on print resolution and ppi, and I think I understand correctly now.

To my understanding, the ppi is totally determined by the size of the image (in pixels) - so essentially there are two methods to size an image for printing:

1) If you want an image of a certain size, resize for that size (eg. 7"x5") and as long as the resulting ppi is more than 300ppi, and the printer can print a certain number of dots per inch, it should be an acceptable quality photo;

OR

2) If you want a certain ppi, plug the desired ppi figure into the software (e.g. Photoshop) and you will get a certain maximum size it can be printed size.....

I'm guessing the best and most common method is the former as people generally want a certain size and not ppi?

Please correct me if I'm wrong as I don't want to mess up with my first client :bonk:
 
remember that 7x5 is not a native aspect for 3:2 sensors and will come out a 7.5x5

if a client wants a 7x5 sell him a 7x5 - keeps the image safe in your hands you only need 2100x1500 pixels at 300dpi
 
Will
The ppi determines the site of the image relative to the number of pixels in that image.

For most purposes the ppi doesn't matter - It only matters when you come to send the print.

It is WRONG to assume that 300ppi is the figure you need to set to get a high quality print. You can send a print at 150ppi (getting 2x the size of print) and still get a perfectly acceptable high quality image from most labs (or home printers).

Plugging the ppi into photoshop therefore does not give a maximum size?

Here's an equation (written 3 ways) - This will allow you to find what you need.

Ps = Print Size
R = Resolution
Px = Pixels

Ps = Px/R
Px = PsxR
R = Px/Ps

So you have a 7x5 image that shows as 549 ppi in photoshop. All that is telling you is that the pixels are packed very tightly together. Look at the number of pixels you have

Px = Ps x R

549 x 7 = 3843
549 x 5 = 2745

That will provide a high quality 7x5 but will also provide a high quality 14x10 at 275ppi and an excellent high qualty image 24" x 17" at 160ppi (noty a standard size but shows that ppi ONLY controls the SIZE of the final print.

My recommendation is to resize for a client to 240ppi and a jpg compression that brigs the file size down to about 500kb. This will restrict the size the image can be printed at.

Sure the client can print at a lower ppi but the compression restricts the quality of the print more. THe image will look perfect at the size you send.

Cheers
Jim
 
POAH said:
remember that 7x5 is not a native aspect for 3:2 sensors and will come out a 7.5x5

if a client wants a 7x5 sell him a 7x5 - keeps the image safe in your hands you only need 2100x1500 pixels at 300dpi
Click to expand...

Thanks for the good advice :)

EOS_JD said:
Will
The ppi determines the site of the image relative to the number of pixels in that image.

For most purposes the ppi doesn't matter - It only matters when you come to send the print.

It is WRONG to assume that 300ppi is the figure you need to set to get a high quality print. You can send a print at 150ppi (getting 2x the size of print) and still get a perfectly acceptable high quality image from most labs (or home printers).

Plugging the ppi into photoshop therefore does not give a maximum size?

Here's an equation (written 3 ways) - This will allow you to find what you need.

Ps = Print Size
R = Resolution
Px = Pixels

Ps = Px/R
Px = PsxR
R = Px/Ps

So you have a 7x5 image that shows as 549 ppi in photoshop. All that is telling you is that the pixels are packed very tightly together. Look at the number of pixels you have

Px = Ps x R

549 x 7 = 3843
549 x 5 = 2745

That will provide a high quality 7x5 but will also provide a high quality 14x10 at 275ppi and an excellent high qualty image 24" x 17" at 160ppi (noty a standard size but shows that ppi ONLY controls the SIZE of the final print.

My recommendation is to resize for a client to 240ppi and a jpg compression that brigs the file size down to about 500kb. This will restrict the size the image can be printed at.

Sure the client can print at a lower ppi but the compression restricts the quality of the print more. THe image will look perfect at the size you send.

Cheers
Jim
Click to expand...

Hi Jim, thanks, that clears a lot up for me now - and thanks for taking the time out to provide a detailed response.
 
Hope you understood ok :)

There is a misconception that you need to provide 300ppi images. You don't.
 
Yes I understood it well - it was well explained (y)

The only thing I'm still thinking is how do I know how large I can print it for the client before the quality starts to degrade too much? I guess I'll have to get some test prints for myself first?
 
Well I've a 30" print at 150ppi and you wouldn't tell the difference from a 6x4!

Remember also that larger images are viewed from slightly further away and the eye resolves less detail the further away you are.

Like I say if you privided a high res image, it's likely it could be blown up pretty big without seeing any degradation by just adjusting the ppi.
 
There is a misconception that you need to provide 300ppi images. You don't.
Click to expand...

There are many people - often magazines (for historical reasons) where its on their spec sheets for adverts and editorial images - and some labs who don't have production software. It also is a waste of resources to supply an image that is oversize - if the client is producing 5x7 inch prints supply them with a jpeg file sized to 5x7 at 300 dpi - a bigger file won't give a better result - in fact often it will give an inferior result due to resampling - and it also give you a chance to sell them a bigger file for bigger prints!

Virtually all photographic printers - Fuji and Noritsu have a native resolution of 300ppi - so thats why 300dpi is specified. In the case of these printers each pixel is capable of all colours so the term is interchangable. If you were printing on an Epson I'd do it at 360ppi as it is their base resolution - as they work at 360, 720, 1440 or 2880 dpi
 
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David you seem to have switched dpi and ppi around :) Corrected

Fuji and Noritsu have a native resolution of 300dpi- so thats why 300ppi is specified

David
When the Epson printers output at 2880dpi their figure includes every dot from each of their print heads. The actual dpi is derived by dividing the resolution used by the number of inks - 2880/8 = 360dpi.

I've sent images at all sorts of resolution to the printer. Be it 140ppi, 150ppi, 180pi, 200ppi, 240ppi, 300ppi I really can't tell the difference!!

Perhaps with a magnifying glass you might but i rarely upsize my documents - althoug with a 5D2 I usually have enough to keep the resolution high.
 
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I keep getting my woking murds fuddled!
 
I pnow the kroblem
 
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