Downsampling for print

[Livin The Dream]

Is it really detrimental to downsample a full-sized image to 300dpi for a standard sized print (10x8). Apart from a smaller file, I can’t see any detriment to IQ. Or is best practice to just change image size and not resample, even for small prints?

 

[PhilH04]

Downsampling from what? It is often regarded as good practice to send 300ppi (not dpi please) to Canon printers or 360ppi to Epson, if using a lab they will specify a ppi value. If using Software such as Lightroom you can specify the output ppi in the print module (I believe you can in PS too...

 

[Harlequin565]

"Most" eyes can't resolve better than 300 dpi at about 12 inches distant, so unless you have people with 20/20 vision scrutinising your images from 4" away (the closest an eye can focus) no one is going to be able to see any issue with downsizing. Some fine art printers will do 720dpi. I've tested both at home and my (old and knackered) eyes can't tell the difference.

tl;dr - no. It isn't detrimental. Mostly.

 

[Livin The Dream]

Downsampling from what? It is often regarded as good practice to send 300ppi (not dpi please) to Canon printers or 360ppi to Epson, if using a lab they will specify a ppi value. If using Software such as Lightroom you can specify the output ppi in the print module (I believe you can in PS too...

It’s dpi for printing, surely. Pixels per inch is monitor resolution ie. the amount of pixel density, or have I missed something completely?

Just looked at Loxley and they specify 300ppi, now I’m confused.

 

[PhilH04]

It’s dpi for printing, surely. Pixels per inch is monitor resolution ie. the amount of pixel density, or have I missed something completely?

Just looked at Loxley and they specify 300ppi, now I’m confused.

It is confusing and the two terms (though wrongly) have become interchangeable these days... It gets complicated, yes dpi is the term used when printing but refers to dots per inch on the paper (it is more complicated). For display on a monitor or for posting on the internet ppi really has no meaning, it is only the pixel dimensions of the image that count, ppi does however have an influence on your final print size. An image will print larger at 150ppi than it will at 300ppi (no resampling). Loxley will specify 300ppi as their printers and RIPs work best with the input at that resolution... Gosh I hope I am making sense....

 

[Livin The Dream]

It is confusing and the two terms (though wrongly) have become interchangeable these days... It gets complicated, yes dpi is the term used when printing but refers to dots per inch on the paper (it is more complicated). For display on a monitor or for posting on the internet ppi really has no meaning, it is only the pixel dimensions of the image that count, ppi does however have an influence on your final print size. An image will print larger at 150ppi than it will at 300ppi (no resampling). Loxley will specify 300ppi as their printers and RIPs work best with the input at that resolution... Gosh I hope I am making sense....

Kinda. I think the confusion, and partly going back to my original question of reduction, is that printers tend to specify 300. I understand the viewing distance theory, but when exporting an image to send to an external printers assume there’s no need to resample, just change dimensions and doesn’t matter if the ppi is higher than 300?

If you resample to 300ppi with bicubic sharper then you’ve reduced the image quality, yet still within the tolerance of what would be noticeable under normal viewing distances, yes?

 

[Harlequin565]

Yes.

At 8x10 sizes you'd have to be Clark Kent to notice the difference.

 

[riddell]

Is it really detrimental to downsample a full-sized image to 300dpi for a standard sized print (10x8). Apart from a smaller file, I can’t see any detriment to IQ. Or is best practice to just change image size and not resample, even for small prints?

No, its not detrimental. It is largely just for file size. Most printers want 300DPI, and those printers are dealing with hundreds if not thousands of images a day. Even a 10% reduction in file makes a huge difference in a short amount of time.

 

[PhilH04]

Not sure what ppi your original images are... printers will normally specify you send them an images at 300ppi as it saves the print driver/RIP from any awkward maths.

 

[Livin The Dream]

Not sure what ppi your original images are... printers will normally specify you send them an images at 300ppi as it saves the print driver/RIP from any awkward maths.

I think the penny has dropped... As long as you resize to the print size you want, it doesn't matter how the pixels are interpolated.

 

[PhilH04]

Yes... having prints prepared by say, Loxley, at 10in x 8in simply send them a file 3000 x 2400 pixels @ 300ppi Personally I do avoid Bicubic Sharper, I find it a bit aggressive, but that is just me. (The crop tool in PS is good for preparing image to size etc.)

 

[StewartR]

I think the penny has dropped... As long as you resize to the print size you want, it doesn't matter how the pixels are interpolated.

I'm not sure whether the penny has dropped in the right place.

Let's suppose you want a 12x8" print, and the printer works at 300 PPI. That 300 is a physical hardware thing. So to make your print, the printer is going to print 3600 x 2400 pixels. It has no choice, it can't do anything else.

So the question is, where does it get those 3600 x 2400 pixels?

If you resize your image to 3600 x 2400 before you send it to the printer, it will simply print exactly what you send it. I think there are obvious advantages to that. You can inspect the file before you send it, you can check that the re-sizing (whether enlarging or shrinking) hasn't had any unwelcome side-effects such as softening or over-sharpening or moiré.

But if you send a file that isn't 3600 x 2400, what actually gets printed? You simply don't know. The printer will have to resize the file to 3600 x 2400 before printing, and you hope it won't have any unpleasant side-effects, but you won't know for sure until you see the print.....

 

[HuntingMartians]

My understanding is DPI is the resolution of the printing ink.

So a 100x100 pixel file printed at 10 PPI would be 10 inches by 10 inches. The DPI is down to the printer and that is how much ink is paid down per inch.

PPI determines printed image size, DPI determines printed ink resolution. That's my understanding.

 

[PhilH04]

My understanding is DPI is the resolution of the printing ink.

So a 100x100 pixel file printed at 10 PPI would be 10 inches by 10 inches. The DPI is down to the printer and that is how much ink is paid down per inch.

PPI determines printed image size, DPI determines printed ink resolution. That's my understanding.

Yes.. and if output to the printer at 100ppi it would print 1in square.

 

[HuntingMartians]

Yes.. and if output to the printer at 100ppi it would print 1in square.

What?

 

[PhilH04]

What?

100 pixel x 100 pixel file output to the printer at 10ppi will print 10 inches x 10 inches.
100 pixel x 100 pixel file output to the printer at 100ppi will print 1 inch x 1 inch.

Edit- I can see where some confusion may arise, had a different head on...
100 x 100 pixels at 10ppi will print 10in x 10in.
100 x 100 pixels at 100ppi will print 1in x 1in.

Hope that makes sense.

 

[StewartR]

100 x 100 pixels at 10ppi will print 10in x 10in.
100 x 100 pixels at 100ppi will print 1in x 1in.

Hope that makes sense.

I'm afraid it doesn't, at least not to me. The key issue I think you're overlooking is that printers can't choose whether to print at 10 PPI or 100 PPI or whatever. The resolution is a hardware thing and as mentioned above it's usually around 300 PPI.

So if you want a 10in x 10in print, the image that is printed has to be 3000 x 3000 pixels. If your image is only 100 x 100 pixels, you're effectively telling the printer to scale it up somehow in order to print 3000 x 3000.

My point is that it's better to handle the scaling yourself, so you send a 3000 x 3000 pixel image to the printer instead of a 100 x 100 pixel image, because that way you know exactly what the effect of the scaling is and you know exactly what you're going to get.

 

[PhilH04]

I'm afraid it doesn't, at least not to me. The key issue I think you're overlooking is that printers can't choose whether to print at 10 PPI or 100 PPI or whatever. The resolution is a hardware thing and as mentioned above it's usually around 300 PPI.

No.... that is DPI not PPI, it is generally accepted that you 'feed' the printer a file at a resolution that is a multiple of its DPI resolution, for Canon Printers that would be 300PPI for Epson it is 360PPI, the printer is not printing at 10PPI or 100PPI, a printer does not print pixels it prints dots.

If your image is 100 x 100 pixels and is at 10PPI it will print at 10in x 10in. if the file is at 100PPI it will print at 1in square.

PPI has no relevance when talking about display on screen, however it does have an effect on the print size.

It does make sense to size your image for printing at the final size at the PPI required by the lab simply because it saves their drivers/RIPs from doing complicated maths.

Try it in Photoshop.

Create a file at 100 x 100 pixels at 10PPI you will see that it will print 10inches square
Create another 100 x 100 pixel file this time at 100PPI and you will see that it will print at 1inch square.

PPI is not a hardware thing, DPI on the other hand is but is unrelated to to print size.

 

[HuntingMartians]

100 pixel x 100 pixel file output to the printer at 10ppi will print 10 inches x 10 inches.
100 pixel x 100 pixel file output to the printer at 100ppi will print 1 inch x 1 inch.

Edit- I can see where some confusion may arise, had a different head on...
100 x 100 pixels at 10ppi will print 10in x 10in.
100 x 100 pixels at 100ppi will print 1in x 1in.

Hope that makes sense.

The only confusion is repeating what I said but changed by a factor of 10. Just didn't understand the need.

 

[HuntingMartians]

I'm afraid it doesn't, at least not to me. The key issue I think you're overlooking is that printers can't choose whether to print at 10 PPI or 100 PPI or whatever. The resolution is a hardware thing and as mentioned above it's usually around 300 PPI.

So if you want a 10in x 10in print, the image that is printed has to be 3000 x 3000 pixels. If your image is only 100 x 100 pixels, you're effectively telling the printer to scale it up somehow in order to print 3000 x 3000.

My point is that it's better to handle the scaling yourself, so you send a 3000 x 3000 pixel image to the printer instead of a 100 x 100 pixel image, because that way you know exactly what the effect of the scaling is and you know exactly what you're going to get.

If you take a 1000 pixel width image and print at 10 inches wide this is printing at 100 pixels per inch irrespective of dpi. DPI is just how much ink is laid down. So you could print at 300 DPI and technically print at 100 ppi.

 

[PhilH04]

The only confusion is repeating what I said but changed by a factor of 10. Just didn't understand the need.

Apologies, I was simply confirming what you said in your post...
"PPI determines printed image size, DPI determines printed ink resolution."
I fail to see how any offence could be taken here. Seems it was though so once again my apologies.

 

[HuntingMartians]

I'm afraid it doesn't, at least not to me. The key issue I think you're overlooking is that printers can't choose whether to print at 10 PPI or 100 PPI or whatever. The resolution is a hardware thing and as mentioned above it's usually around 300 PPI.

So if you want a 10in x 10in print, the image that is printed has to be 3000 x 3000 pixels. If your image is only 100 x 100 pixels, you're effectively telling the printer to scale it up somehow in order to print 3000 x 3000.

My point is that it's better to handle the scaling yourself, so you send a 3000 x 3000 pixel image to the printer instead of a 100 x 100 pixel image, because that way you know exactly what the effect of the scaling is and you know exactly what you're going to get.

PPI determines print size basically.

DPI determines how much ink to put down for the image.