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### AuthorTopic: print vs LR resolution  (Read 16368 times)

#### alifatemi

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##### print vs LR resolution
« on: December 17, 2013, 12:42:03 am »

what is the relation/difference between printer resolution, say 28800 DPI and in LR, say, 360 PPI? How can you calculate for a given size of a  print, what amount of PPI and DPI should be chosen for having the best possible fine art print? I have read Jeff Schewe Digital Print, but either I could not understand or he misses to elaborate the matter; In page 129 of his book, comparing iPhone with P65 print resolution, he says the iPhone resolution is not sufficient to print 18.7x24.9 because resolution comes down to 132PPI; okay but what is the calculation Jeff? How do you find out? in LR, when you change the print size in Print module and print resolution tab is unchecked, resolution of print changes while you change the print size and it shown on the upper left side of the picture; what is the formula? how LR calculate that? when you check the resolution tab in LR and changing the print size, how should I find out what resolution should I chose for a given print size for best quality?
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#### ErikKaffehr

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##### Re: print vs LR resolution
« Reply #1 on: December 17, 2013, 01:01:03 am »

Hi,

Printer resolution is in dots. Printers use just a few colours, so each colour is built by many small dots. So DPI is not related to PPI.

At close viewing distance, the resolution of the human eye is close to 360 PPI, for normal vision. So 360 pixels are excellent for normal prints. No mistake, 180 PPI are quite enough for excellent prints, too. Below 180 PPI you start to see some detoriation in mage quality.

There is something called Vernier acuity, the eye can detect discontinous lines, even if the displacement is lower than normally resolved. So for images with lines, or well defined edges 720 PPI may be helpful.

Best regards
Erik

what is the relation/difference between printer resolution, say 28800 DPI and in LR, say, 360 PPI? How can you calculate for a given size of a  print, what amount of PPI and DPI should be chosen for having the best possible fine art print? I have read Jeff Schewe Digital Print, but either I could not understand or he misses to elaborate the matter; In page 129 of his book, comparing iPhone with P65 print resolution, he says the iPhone resolution is not sufficient to print 18.7x24.9 because resolution comes down to 132PPI; okay but what is the calculation Jeff? How do you find out? in LR, when you change the print size in Print module and print resolution tab is unchecked, resolution of print changes while you change the print size and it shown on the upper left side of the picture; what is the formula? how LR calculate that? when you check the resolution tab in LR and changing the print size, how should I find out what resolution should I chose for a given print size for best quality?
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Erik Kaffehr

#### Slobodan Blagojevic

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##### Re: print vs LR resolution
« Reply #2 on: December 17, 2013, 01:06:15 am »

Formula: file size (pixels) / paper size (inches) = print resolution (pixel per inch or PPI)

#### alifatemi

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##### Re: print vs LR resolution
« Reply #3 on: December 17, 2013, 01:15:38 am »

thanks Slobodan but give me an example; file size of RAW or tiff or doesn't matter?
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#### ErikKaffehr

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##### Re: print vs LR resolution
« Reply #4 on: December 17, 2013, 01:24:21 am »

Hi,

Slobodan says file size in pixels.

Say that the image is 6000x4000 and you print A2 (23x16"). PPI would be 6000/23 = 260, that would make an excellent print.

It would be best to resize the image to 360 PPI (Epson) or 300 PPI (Canon) before sending to the printer, as Lightroom or Photoshop have better interpolation than printer drivers. Also, the image needs some sharpening before printing and that kind of sharpening (output sharpening) is best done in LR. Or you can use a program like QImage that handles resizing and so.

Best regards
Erik

thanks Slobodan but give me an example; file size of RAW or tiff or doesn't matter?
« Last Edit: December 17, 2013, 01:28:16 am by ErikKaffehr »
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Erik Kaffehr

#### hugowolf

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##### Re: print vs LR resolution
« Reply #5 on: December 17, 2013, 01:26:40 am »

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#### Schewe

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##### Re: print vs LR resolution
« Reply #6 on: December 17, 2013, 01:57:34 am »

How do you find out? in LR, when you change the print size in Print module and print resolution tab is unchecked, resolution of print changes while you change the print size and it shown on the upper left side of the picture; what is the formula? how LR calculate that? when you check the resolution tab in LR and changing the print size, how should I find out what resolution should I chose for a given print size for best quality?

To determine the output resolution of a print, divide the native resolution of the image by the dimension chosen for a print. If the image has a native resolution of 21MP (like the 1DsMIII) which is 5616 x 3744 pixels and you wanted a 10 x 6.6 print, the resolution in terms of pixels per inch would be 561.6 PPI. You can also divide the native resolution by the desired output print resolution and determine the print size. That same 21MP capture would work out to 18.72 x 12.48 inches at 300 PPI or 15.6 x 10.4 inches at 360 or 31.2 x 20.8 at 180 PPI.

In terms of the resolution you "need" for a print, that depends on viewing distance because human vision resolution is dependent on the viewing distance. The close you hold a print to your eyes, the more resolution that your eyes can resolve. There's a chart on page 129 that tells you the eye's resolvable resolution. A couple of examples: viewing distance of 8 inches would require 428 PPI in PPI resolution. From 18 inches you would need 191 PPI.

From an article I did for Digital Photo Pro magazine called The Right Resolution I wrote about what Bruce Fraser wrote about human vision acuity:

Resolution And The Eye
My good friend and colleague, the late Bruce Fraser, wrote about human visual acuity in his Real World Image Sharpening book (which I've taken over as coauthor for him). In the book, Bruce indicated that "the generally accepted definition of normal (20/20) visual acuity is the ability to resolve a spatial pattern whose features are separated by one minute of arc, or 1⁄60 of a degree." Unfortunately, that doesn't translate to printer-output resolution very easily. It involves trigonometry and calculations, which I hate. Fortunately, Bruce already did the math as shown in the table below.

Viewing Distance (in inches)                 Resolution the eye can resolve (DPI)
8"                                                    428
10"                                                  355
12"                                                  286
18"                                                  191
24"                                                  143

As you can see, the closer the distance, the more resolution the eye can see when expressed as dots per inch (dpi). The normal viewing distance of a print is typically between 1.5 and 2 times the diagonal of a print. So a 3.5x5-inch print normally would be viewed from between 10 and 12 inches away, and the eye could resolve between 355 dpi and 286 dpi.

In terms of determining the usable range of output resolution, Bruce thought that depending on print size, you needed at least 180 PPI to a max of 480 PPI. However, I've found that depending on the printer, you can tell the difference up to about 720 PPI (assuming Epson, or 600 PPI for Canon or HP). This type of resolution is really only useful for small printsâ€“which is handy because you'll have higher output resolution when making small sized prints.

The output resolution requirement is, of course, impacted by the size, printer, media and how well the original image was captured, and how the image and print was sharpened. Textured media is far more forgiving while glossy media requires as much resolution as you can give it.

In terms of the difference between image resolution and printer resolution, the output resolution of printers refers to droplets/inch. So, at 2880 the Epson printers put 2880 droplets of ink/inch. In terms of dots/inch, that's a different measurementâ€“printers report their resolution to the print pipeline as dots/inch (DPI) which is a different measurement unit...Epson printer report 360 DPI which Canon HP report 300 DPI. There are driver modes that can change the reported resolution; Finest Detail makes Epson printers report 720 DPI while Canon & HP can be set to report 600 DPI.

Confused yet? Go back and reread the section in the book...
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#### alifatemi

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##### Re: print vs LR resolution
« Reply #7 on: December 17, 2013, 04:18:04 am »

Thanks a lot Jeff! not confused any more but just assume that I have D800 with native resolution of 7360 so I can print as big as 20" with 360 PPI but what if I like to print the same file on 40" paper with same 360PPI? Is it possible at all?
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#### bjanes

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##### Re: print vs LR resolution
« Reply #8 on: December 17, 2013, 08:02:03 am »

Thanks a lot Jeff! not confused any more but just assume that I have D800 with native resolution of 7360 so I can print as big as 20" with 360 PPI but what if I like to print the same file on 40" paper with same 360PPI? Is it possible at all?

You could try a specialized upresing algorithm such as Perfect Resize or PhotozoomPro. While these algorithms can not create image detail, they can fake it up to a limit. You can search this forum for opinions. One thread is here.

Bill
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#### hjulenissen

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##### Re: print vs LR resolution
« Reply #9 on: December 17, 2013, 08:12:19 am »

I think that worrying about DPI and PPI just might have made sense back when pixel grids were the main limiting factor.

For current pixel densities, I believe that this is no longer the case (if your D800 images are sharp right down to the sensel grid or close to it, then you probably don't need to worry about ppi).

-h
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#### hjulenissen

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##### Re: print vs LR resolution
« Reply #10 on: December 17, 2013, 08:14:45 am »

There is something called Vernier acuity, the eye can detect discontinous lines, even if the displacement is lower than normally resolved. So for images with lines, or well defined edges 720 PPI may be helpful.
I have seen this point raised a few times. I have never seen it discussed related to "proper" (re)sampling.

If your camera has "proper" pre-filtering, and your printer/display apply the equivalent of proper post-filtering, then a thin-ish line can be displaced by subpixel amounts. Of course, the sampling systems (and resampling) of imaging leaves a lot to be desired, but it is not simple point-samplers, either.

-h
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#### Bart_van_der_Wolf

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##### Re: print vs LR resolution
« Reply #11 on: December 17, 2013, 08:43:00 am »

I have seen this point raised a few times. I have never seen it discussed related to "proper" (re)sampling.

If your camera has "proper" pre-filtering, and your printer/display apply the equivalent of proper post-filtering, then a thin-ish line can be displaced by subpixel amounts. Of course, the sampling systems (and resampling) of imaging leaves a lot to be desired, but it is not simple point-samplers, either.

Hi,

Proper resampling will require subsequent (deconvolution) sharpening to remove some of the resampling blur. The required PSF can be approximated by resampling a slanted edge and analyzing the result.

Cheers,
Bart
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#### hjulenissen

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##### Re: print vs LR resolution
« Reply #12 on: December 17, 2013, 09:24:49 am »

Hi,

Proper resampling will require subsequent (deconvolution) sharpening to remove some of the resampling blur. The required PSF can be approximated by resampling a slanted edge and analyzing the result.

Cheers,
Bart
Not sure if you are saying that Vernier acuity can be used for estimating thresholds of visible distortion or not?

My point is that subpixel movement is possible in "properly filtered" systems. Claiming that vernier acuity of some n-th fraction of a degree warrants a pixel density of the same order should be accompanied by some further insight/data/arguments.

Given (primitive) sequences
A:[0 0 0 0.9 0.1 0 0 0]
B:[0 0 0 0.1 0.9 0 0 0]

There can be little doubt that the "blip" is moved to the left in sequence A by a subpixel amount compared to sequence B. (its weight is also unchanged, but its detailed shape is different). As far as I understand Vernier acuity, such simple movement of the blip centrum may (or may) not satisfy our capability of Vernier distinction.

-h
« Last Edit: December 17, 2013, 09:29:04 am by hjulenissen »
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#### Slobodan Blagojevic

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##### Re: print vs LR resolution
« Reply #13 on: December 17, 2013, 09:33:47 am »

Are you guys serious!?

#### Jason DiMichele

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##### Re: print vs LR resolution
« Reply #14 on: December 17, 2013, 09:58:05 am »

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#### Bart_van_der_Wolf

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##### Re: print vs LR resolution
« Reply #15 on: December 17, 2013, 10:00:48 am »

Not sure if you are saying that Vernier acuity can be used for estimating thresholds of visible distortion or not?

Vernier acuity exceeds normal (20/20) visual acuity. It depends on the subject/micro-contrast how significant Vernier acuity is for the output, but up-sampling will lower the PPI limit of 20/20 vision, so it's best to properly sharpen after up-sampling to keep as much intact as possible.

Upsampling algorithms like Photozoom's S-Spline Max, will add resolution and that may help even more.

Cheers,
Bart
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#### hjulenissen

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##### Re: print vs LR resolution
« Reply #16 on: December 17, 2013, 10:15:10 am »

Vernier acuity exceeds normal (20/20) visual acuity. It depends on the subject/micro-contrast how significant Vernier acuity is for the output, but up-sampling will lower the PPI limit of 20/20 vision, so it's best to properly sharpen after up-sampling to keep as much intact as possible.

Upsampling algorithms like Photozoom's S-Spline Max, will add resolution and that may help even more.
If one is to reproduce figures like the one below, using a camera and display/printer, I think that proper (linear) filtering is more important than fancy nonlinear processing. Yes, the end-to-end filtering will cause blurring, but the whole point of Vernier seems to be that the width and exact shape of the line does not matter as much as its placement. So a certain amount of blurring should be visually transparent (at some scale, say on the order of 1 minute of arc or some fraction of that. What matters (wrgt Vernier) is that the weight of the line can be recorded and recreated accurately.

This is the opposite of the current trend of OLPF-less cameras: when you sample without prefiltering, you (usually) loose accurate information about subpixel placement, but you gain pixel-pixel contrast.

-h
« Last Edit: December 17, 2013, 10:17:28 am by hjulenissen »
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#### Slobodan Blagojevic

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##### Re: print vs LR resolution
« Reply #17 on: December 17, 2013, 10:51:06 am »

Oh, I see, you ARE serious.

A guy stops to asks for directions to the nearest gas station, and you engage in a post-doctoral dissertation on the properties of space rocket fuel!?

#### Bart_van_der_Wolf

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##### Re: print vs LR resolution
« Reply #18 on: December 17, 2013, 11:42:05 am »

Oh, I see, you ARE serious.

A guy stops to asks for directions to the nearest gas station, and you engage in a post-doctoral dissertation on the properties of space rocket fuel!?

C'mon Slobodan,

A guy asks question about print resolution. What do you expect, that we start posting off-topic way too small images about tonality, like this:

Cheers,
Bart
« Last Edit: December 17, 2013, 12:41:07 pm by BartvanderWolf »
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#### Bart_van_der_Wolf

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##### Re: print vs LR resolution
« Reply #19 on: December 17, 2013, 11:51:26 am »

What matters (wrgt Vernier) is that the weight of the line can be recorded and recreated accurately.

Yes, and with adequate contrast. But that leads to stating the obvious, that nothing beats real resolution, and that lacking that we need proper re-sampling, and proper sharpening.

Cheers,
Bart
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