Getting the Right Print Size

[Nicks Pics]

I asked a printing service what type of file I should send in for printing. They told me to send jpeg at 300 dpi. I looked at my editing programs and couldn't find anywhere to set a dpi number for my images, only a ppi. I read some about it, including re-reading posts on CinC and what I am understanding you should do is to multiply the image dimensions by the dpi number. 8x10 x 300 = 2400x3000, so I should resize the image to 2400x3000 pixels, in this case it increases the size of the image. Is that the correct way to make a 8x10 picture capable of printing 300 dpi? Because I don't see anywhere on my software to set a dpi number; dpi is a printer setting, I think. I don't know if I actually can send the printing service a 300 dpi image.

If you have any quick confirmation or correction of how to do this that would be appreciated. Thank you

[Shadowman]

Lightroom allows you to set dpi.

[Nicks Pics]

Somehow I haven't found where in LR you can set dpi? I am using LR 4 if that makes any difference. BTW how does it make sense to set a dpi number in the image editor? Theoretically you could set an image to 300 dpi in the editor then send it to a printer that was not set to 300 dpi and it wouldn't print 300 dpi-or perhaps I'm confused about something. Thanks though.

[pnodrog]

In LR4 when you use the export function you get the options of setting pixel dimensions, whether you wish to enlarge images that are smaller than the pixel size chosen, dpi (ppi is not but is effective the same thing) and any or level of output sharpening required.



You can do it via the Print module but I only use that for an attached printer.

[Mike Buckley]

Notice the drop down menu in L. Paul's screenshot indicating "pixels." If LR4 behaves the same as LR5, you can change that menu to display the dimensions in inches or centimeters. However, the resolution in that dialog menu is provided only in pixels, not dots. That being the case, the physical dimensions in inches or centimeters do not change when changing the resolution. (I would argue that it should be impossible to display the dimensions in inches or centimeters when it's not possible to display dots per inch, but that's for another thread despite that that might be an understandable source of your confusion.)

In that sense L. Paul is correct that you can think of pixels per inch and dots per inch being one and the same but only if you are also willing to ignore the physical dimensions being displayed in that dialog menu. Instead, you would rely on the calculation that you already understand.

When software displays dots per inch, the display of physical dimensions of the print size should automatically change when you change the number of dots per inch. I've never used LR's print module. Hopefully it does that.

[Nicks Pics]

Thank you all for your responses. I know you can change the number of pixels per inch, but still I don't see anywhere to change dpi. So with the image dimensions (in inches) x desired dpi (say 300) what is this but making the pixels equate to what the dpi will be? I guess it is about the same?

[Mike Buckley]

I just now looked at the LR5 Print module and you're right that it displays only the ppi, not the dpi. As far as I'm concerned, that's just plain wrong. Even so, your solution is to "think" dpi even when the display indicates ppi.

Pixels will never be dots and dots will never be pixels, so just ignore that dots should be the unit that is displayed rather than pixels. LR is not the only software that displays those units inaccurately, causing unnecessary confusion in the process.

EDIT: Se Dave's email immediately below.

[davidedric]

Actually, guys, ppi is correct. It is the resolution of the image that Lightroom sends to the printer, nothing to do with the final print resolution. It's recommended that you send the image in the "native resolution" of the printer which for Canon is 300 ppi, so that the operating system doesn't muck around with it, and the printer drivers can convert that to what they need to print.

Agree it is confusing, but I am sure that is correct.

Dave

[Mike Buckley]

I think you're right, Dave, and I have edited my above post. I'm absolutely sure that you're right about it being confusing.

The following is from Adobe Lightroom CC Help:

"In the Print module, the Print Resolution setting specifies the pixels per inch (ppi) of the photo for the printer. Lightroom resamples the image data if needed, depending on the print resolution and the print dimensions. The default value of 240 ppi is satisfactory for most print jobs, in cluding high-end inkjet prints. Refer to your printer’s documentation to determine its optimal resolution."

In that context, it actually makes sense. You have cleared this up for me for the first time. Thanks!

[Nicks Pics]

Actually, guys, ppi is correct. It is the resolution of the image that Lightroom sends to the printer, nothing to do with the final print resolution. It's recommended that you send the image in the "native resolution" of the printer which for Canon is 300 ppi, so that the operating system doesn't muck around with it, and the printer drivers can convert that to what they need to print.

"In the Print module, the Print Resolution setting specifies the pixels per inch (ppi) of the photo for the printer. Lightroom resamples the image data if needed, depending on the print resolution and the print dimensions. The default value of 240 ppi is satisfactory for most print jobs, in cluding high-end inkjet prints. Refer to your printer’s documentation to determine its optimal resolution."

Thanks Mike and Dave for helping explain. I think that makes sense, as far as the software is concerned, and now I must apply that to how I should send my photo (s) to the printing service. My guess is that I should send in 300 ppi per the print service's recommendation that I should send photos in "300 dpi" supposing that they meant 300 ppi, because 300 ppi files work best with their printer. They can print it at 300 dpi, but I can't because I'm not running the printer

[davidedric]

Hi Nick,

Yes, that's how I understand it works. The only thing I would add is that a modern pro printer can print much finer than 300 dpi. A Canon Pro 100 can manage up to 4,800 dpi. The clever bit is how it interpolates from your image file to the higher print resolution.

Dave

[Inkanyezi]

Many people are confused about DPI and even professional printers sometimes state DPI, when they actually want the image size in PPI (Pixels Per Inch). My take on it is that printers often use a term "points" that is a quite different entity, relating to the size of characters in print, not the actual dots a printing system handles, neither the pixels of a raster image. So resisting to using "PPI" thinking about Points, they use the term DPI, messing up completely, as the printer dots are only very loosely related to our pixels. But we want to know how many pixels to send them, not the inches.

So they actually want Pixels Per Inch, although they state Dots Per Inch. Make your calculations based on the printed size in inches.

In the printer, each pixel will print with a multitude of dots, the minimum being about 25, in which case the pixels per inch will correspond to about five times as many dots, as the pixel is a square, but the inch is a length measure. However, the actual dots may often be many more, or sometimes less.

[Nicks Pics]

Hi folks, Thanks for your help in explaining!

Hi Inkanyezi

You also made a helpful post on another thread about print sizes, so thanks for sharing your advise.



My general conclusion at this point is that the printing service says and even states on their website to send files at 300 dpi, but really they should be saying 300 ppi, comparable to what Dave is saying here.

It's recommended that you send the image in the "native resolution" of the printer which for Canon is 300 ppi, so that the operating system doesn't muck around with it, and the printer drivers can convert that to what they need to print.

300 ppi is their printers' native resolution. As for dpi, I can disregard that for now because I''m not running the printer, and who knows what setting they are printing at. It could be 300 pixels per inch, 25 dots per pixel

In the printer, each pixel will print with a multitude of dots, the minimum being about 25, in which case the pixels per inch will correspond to about five times as many dots, as the pixel is a square, but the inch is a length measure. However, the actual dots may often be many more, or sometimes less.

or either more or less.

Anyway, I hope my print will look okay

[Mike Buckley]

Anyway, I hope my print will look okay

After going to all this trouble, just make sure you send the correct image.

[Nicks Pics]

After going to all this trouble, just make sure you send the correct image.

Well, sometimes it can be hard to figure out which edit version I wanted to use