Resize for print PPI

[Clonetrooper]

Just a quick check as it's been years since I printed and I'm sure I asked this the last time but cannot find the thread. I'm about to send a few files to DSCL that I want 15x10 inches. They state:

All images should be supplied as sRGB or with our own profiles as JPEG files at 300 dpi and sized to the correct output size required.

Now am I correct, on export I just change the below to Width to 3600 (240x15) and height 2400 (240x10) or am I best to just upload the file and let them scale when I select a 15x10 image?

Why do they even mention DPI as I can't alter that, if I remember correctly that's on their hardware?

Thanks for any help

 

[Kodiak Qc]

•


To make it easier for you,

w= 15
h= 10

If you want a vertical frame, swap the values.

pixels= select "inches"
resolution= up to 300 ppi.

 

[PhilH04]

•


To make it easier for you,

w= 15
h= 10

If you want a vertical frame, swap the values.

pixels= select "inches"
resolution= up to 300 ppi.

Even easier assuming your image is the correct proportions i.e 3 : 2, instead of "Width & Height" select "Long Edge" you will only have one box to fill in now, change the units to Inches and enter 15. Change the ppi to 300 and away you go.... will be good for either portrait or landscape format.

ppi and dpi are often wrongly used interchangeably even when they are supposedly experts, it should indeed read ppi. (it drives me nutty BTW)

 

[Clonetrooper]

Thanks so I need to change that Resolution box to 300, if I didn't and still selected 15x10 would it impact the quality that much?

Thanks again for the replies

 

[Kodiak Qc]

…so I need to change that Resolution box to 300?

No, you don't have to.

It all depends on the viewing distance to the print.
The closer = the higher. A magazine is meant to
be read rather close so the resolution needs to be
250 to 300ppi. On a wall, at a distance of say 8', 98
to 150 ppi is ok for the same size.

 

[gerry s]

If they have asked for 300 why not just do it

 

[Kodiak Qc]

If they have asked for 300 why not just do it

They know that not all their clients are savvy so
they prescribe the easier solution… do it as they
want but I wished to help you understand the dif-
ferences.

 

[Harlequin565]

Thanks so I need to change that Resolution box to 300, if I didn't and still selected 15x10 would it impact the quality that much?

15x10 at 300 ppi is 4500 x 3000 pixels. The quality of a 15x10 without specifying ppi would depend on the original image size (or your camera sensor size if you haven't cropped it).

e.g. My (X-T2) sensor is 6000x4000 so a 15x10 print would print "natively" at 400ppi which would be more than enough. If I tick the box to state 300 dpi, the Lightroom will downsize the image (slightly)

However if you had a Canon 350D which has a 3456x2304 sensor, the print would "natively" be about 230ppi - still probably "good enough". If you were to tick the 300ppi box, this time Lightroom would enlarge the image (slightly)

I suspect DSCL state 300ppi to stop complaints of "it's pixelated, gimme my money back!" and it's easier to broad brush tell people "you need 300ppi" than it is to explain resolution and viewing distance to people who don't care/aren't interested.

 

[PhilH04]

The reason for 300ppi has good grounding in sending a resolution to the printer driver that will require the least amount of maths and rounding by said driver. When resized or resampled by the driver the algorithm used is probably not the best.

The reasoning is to send 300/600ppi to the driver for Canon printers and 360/720ppi for Epson.

When using lightroom for printing via the print module the resizing/resampling algorithms are adaptive and the print sharpening amount is taken into account too, there is a recommendation to only enlarge/uprez.

DSCL (I can't say for definite as I do all my own printing) probably use a system that benefits from a native 300ppi input (it could be Durst Lamba or Fuji Frontier). Feeding it with a correctly sized image at a lower ppi probably won't hurt, the driver will just have to work a bit harder for its living.

Something else I should perhaps have mentioned earlier is that the print module in LR is great for preparing and outputting files for external printing you have full control over layout, size, required colour space and you can simply output to a JPEG at the required ppi.