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Author Topic: How do I determine which DPI to use when export in LR?  (Read 4205 times)

DFM

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Re: How do I determine which DPI to use when export in LR?
« Reply #15 on: June 27, 2013, 06:12:59 AM »
PPI (Pixels Per Inch, which are different from Dots Per Inch) will decide the number of pixels in the exported image only if you set the Image Sizing measurement unit to inches or cm instead of pixels. If you stick to the default of pixels, it has no effect whatsoever. The only reason for showing physical units on that dialog is to help you do the math.

PPI is a tag in the JPEG header which tells third-party software how to calculate the "100%" physical size of the image, for example when placing it into another document or starting the page setup for a printout with "use actual size" selected. It doesn't affect image quality, sharpening, etc. in any way. In the attached 100% crop of some laser engraving, the left side was exported at 1200PPI and the right side at 12PPI (print sharpening enabled).

When printing from any pixel-based format, the image size (in pixels) and the scaling factor (in percent) are all that matter. If you export a 1000x1000 pixel JPEG file at 300PPI, and another one at 30PPI, then use 'fit to page' when printing, the result will be identical. However, drop them into a Word file and the second one will be zoomed like crazy.

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Re: How do I determine which DPI to use when export in LR?
« Reply #15 on: June 27, 2013, 06:12:59 AM »

docholliday

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Re: How do I determine which DPI to use when export in LR?
« Reply #16 on: June 27, 2013, 06:54:30 AM »
On my 44" printer, I always try to aim for at least 300dpi (Canon/HP) or 360dpi (Epson) for "optimal" quality prints.

jeff schewes says for the new epsons 720 DPI is the best setting.
if you have the pixels to reach this without upscaling.

there is a whole LL video about this, worth watching.


Quote
The export CAN make a difference - 300 vs 400 dpi is how many dots per inch. If exported too low (try printing an exported RAW 96dpi 8x10 and then a 400dpi 8x10 from the same file), the output software/driver/engine will have to interpolate to make up the extra pixels needed and the pixels will virtually be "larger". This will reduce the perceptual gradation smoothness. But, there is a point where it is overkill.

correct me if im wrong but setting the DPI in LR will not RESAMPLE the image?!
so it doesn´t matter.

you can set PIXEL to 1920 pixels and change the DPI to whatever you want... LR will still export a 1920 pixel image. so it doesn´t really matter. you can still set the DPI when you actually going to  PRINT the image.

i don´t know for sure because i only print from photoshop and i never use the DPI setting in LR´s export dialog.
but it should not resample the image i think. that´s what the PIXEL option is for.

LR won't resample the image, but the printing app will a 1900px image at 100dpi will be 19" at native res. at 200dpi, it'll be 950px. If you set the 200dpi and still want 19", it'll have to interpolate an extra 950px into the image to make it work (or print the existing pixels at twice their size).

So, yes, it does matter.

With the Epson printers - it depends on what the NATIVE resolution of the print engine is. If it's a 720x360 engine, then 360 would be the default. If it's a 720x720 engine (or 1440x720), it'd be 720dpi. I've printed stuff as low as 100dpi on a 60" print and looked great displayed. Nobody who viewed it knew how low the resolution was. Of course, it was mounted in a gallery where the viewers couldn't get closer than about 15' from it (over a balcony on the other side wall).

Pi

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Re: How do I determine which DPI to use when export in LR?
« Reply #17 on: June 27, 2013, 07:27:47 AM »
PPI (Pixels Per Inch, which are different from Dots Per Inch) will decide the number of pixels in the exported image only if you set the Image Sizing measurement unit to inches or cm instead of pixels. If you stick to the default of pixels, it has no effect whatsoever. The only reason for showing physical units on that dialog is to help you do the math.

PPI is a tag in the JPEG header which tells third-party software how to calculate the "100%" physical size of the image, for example when placing it into another document or starting the page setup for a printout with "use actual size" selected. It doesn't affect image quality, sharpening, etc. in any way. In the attached 100% crop of some laser engraving, the left side was exported at 1200PPI and the right side at 12PPI (print sharpening enabled).

When printing from any pixel-based format, the image size (in pixels) and the scaling factor (in percent) are all that matter. If you export a 1000x1000 pixel JPEG file at 300PPI, and another one at 30PPI, then use 'fit to page' when printing, the result will be identical. However, drop them into a Word file and the second one will be zoomed like crazy.

+1
Bottom line, ignore the DPI. It has very specific applications, and you will likely not need to worry about them.

Malte_P

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Re: How do I determine which DPI to use when export in LR?
« Reply #18 on: June 27, 2013, 07:54:13 AM »
On my 44" printer, I always try to aim for at least 300dpi (Canon/HP) or 360dpi (Epson) for "optimal" quality prints.

jeff schewes says for the new epsons 720 DPI is the best setting.
if you have the pixels to reach this without upscaling.

there is a whole LL video about this, worth watching.


Quote
The export CAN make a difference - 300 vs 400 dpi is how many dots per inch. If exported too low (try printing an exported RAW 96dpi 8x10 and then a 400dpi 8x10 from the same file), the output software/driver/engine will have to interpolate to make up the extra pixels needed and the pixels will virtually be "larger". This will reduce the perceptual gradation smoothness. But, there is a point where it is overkill.

correct me if im wrong but setting the DPI in LR will not RESAMPLE the image?!
so it doesn´t matter.

you can set PIXEL to 1920 pixels and change the DPI to whatever you want... LR will still export a 1920 pixel image. so it doesn´t really matter. you can still set the DPI when you actually going to  PRINT the image.
i don´t know for sure because i only print from photoshop and i never use the DPI setting in LR´s export dialog.
but it should not resample the image i think. that´s what the PIXEL option is for.

LR won't resample the image, but the printing app will a 1900px image at 100dpi will be 19" at native res. at 200dpi, it'll be 950px. If you set the 200dpi and still want 19", it'll have to interpolate an extra 950px into the image to make it work (or print the existing pixels at twice their size).

So, yes, it does matter.

it doesn´t matter what DPI you set in LR as long as you make the correct settings in the app you print with. it´s not an irreversible setting that alters the quality (like resampling)... that´s what i mean.

Quote

Quote
jeff schewes says for the new epsons 720 DPI is the best setting.

With the Epson printers - it depends on what the NATIVE resolution of the print engine is. If it's a 720x360 engine, then 360 would be the default.

yes and the new espons should have 720DPI.


« Last Edit: June 27, 2013, 07:59:46 AM by Malte_P »

CarlTN

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Re: How do I determine which DPI to use when export in LR?
« Reply #19 on: June 29, 2013, 03:18:15 AM »
This is an interesting thread full of great info.

I must disagree that you can never print anything larger than the native resolution at say 300 dpi.  I have had a 20x30 inch print done from a mere 15MP camera, which I scaled using only CS5 (I have since bought the Perfect photo suite 7, which works even better for enlargements).  The resolution of the final jpeg I sent to the printer, was a 20x30 inch image at 300 dpi.  You can get less than 1 foot from the print and it looks sharp.  Of course the image was maximally sharp to begin with.  But just because the native resolution of the camera was far lower than this, does not mean the print is not sharp...let alone not even useful.  The client must have been happy with it, because it is hanging in the lobby.

barfbaggs

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Re: How do I determine which DPI to use when export in LR?
« Reply #20 on: July 03, 2013, 05:55:08 PM »
I spent 20 years in commercial printing and prepress, and can tell you that the general rule is that an image printed at 100% size should have a dpi of twice what the line screen is that your printer will be using. The printer you select will generally ask you to select the line screen (ls), or provide you with what their standard is. Most standard magazines are printed at 133ls, 150ls and 175ls, so for an image printed at those line screens, you would optimally need 266dpi, 300dpi, and 350dpi respectivley. Higher end publications are generally printed at 200ls to 300ls, with those requiring dpi's of 400 and 600 respectively. All of our proofing on large format Epsons is processed using those same files with the same settings. To sum it up, use a dpi of twice the line screen to print at 100%. 10% less than double will likely be unnoticeable, and anything more than double does not hurt but may add slightly to file processing times.

Pi

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Re: How do I determine which DPI to use when export in LR?
« Reply #21 on: July 03, 2013, 10:24:53 PM »
I believe that many posts miss the OP's point. DPI in LR just writes a flag in the EXIF, and it is not used as a basis for resizing the image. For most practical purposes, that flag is completely irrelevant.

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Re: How do I determine which DPI to use when export in LR?
« Reply #21 on: July 03, 2013, 10:24:53 PM »

duydaniel

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Re: How do I determine which DPI to use when export in LR?
« Reply #22 on: July 07, 2013, 06:38:46 PM »
I believe that many posts miss the OP's point. DPI in LR just writes a flag in the EXIF, and it is not used as a basis for resizing the image. For most practical purposes, that flag is completely irrelevant.

I have learned quite a lot!!!
Thank you guys

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Re: How do I determine which DPI to use when export in LR?
« Reply #22 on: July 07, 2013, 06:38:46 PM »