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FORUMS Post Processing, Marketing & Presenting Photos RAW, Post Processing & Printing 
Thread started 19 Nov 2016 (Saturday) 16:42
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LR Resolution

 
tzalman
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Post edited over 4 years ago by tzalman.
     
Nov 20, 2016 01:55 as a reply to  @ post 18189471 |  #16

JPGs have identical sizes and differ in only a few dozen bytes, perhaps bytes having to do with housekeeping like creation time.

Note that I wrote that the difference is not in image size but rather in the LR/CR sharpening applied at output (sharpening that Adobe outsourced to Pixel Genius, makers of the PhotoKit Sharpener plugin for PS) and frequently the difference is at pixel-peeper level.
Nevertheless, it is worthwhile to be aware that LR's Output Sharpening: Screen comes in six flavors; the Low, Standard, High settings are multiplied by two, ppi<150 and ppi>150


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BigAl007
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Nov 20, 2016 05:54 |  #17

Resolution is a required field in the EXIF standard, and as such you HAVE to have some value in the field for you to have a valid file. Staying away from LR specifics for a moment, if you are going to produce use specific files chosing the correct value for the tag can make a big difference to the user of the file. Having an appropriate value is still very important for images that will be used in DTP for example, where programs like InDesign will automatically use the tag to size the image on the page. Although sending a 3000×2000 pixel image for use in a magazine is usually fine, people are unlikely to be happy if you constantly tag it 72 PPI, and the software lays out a 41.67"×27.78" image on the page. They will want the image tagged 300 PPI so that the image is layed out at 10"×6.67", a much more reasonable size, considering the paper size of most magazines. When I both edited and published the matchday program for my local non-leauge football club, I would actually import all of the images I was supplied with into LR, just so that I could export them all apropriatly. It was much easier to do this extra step, and have consistent files to deal with in InDesign, than deal with each image individually as they were placed in the document. I have also dealt with some widely distributed UK magazines, and they still ask for images to be a certain physical size at usually 300 PPI, because that's all most of the people who you get to talk to know.

As to the difference in sharpening from LR, it's Sunday, and the weather isn't great so I feel an experiment coming on to see if there are pixel level differences to be seen at different settings.

Alan


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Archibald
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Nov 20, 2016 09:48 |  #18

Go for it, Alan. All is revealed in experiments.

It is a bit of a commentary on a program like LR when experienced users don't agree one on of its common features, and can't succinctly describe it!

Perhaps what that really says is that it doesn't matter much.


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Nov 20, 2016 12:00 |  #19

Ok so I ran some quick tests, and here are my results. Firstly I will describe how I measured the results of the sharpening applied, I did this by simply loading all of the exported files as layers in PS and setting the blend mode to difference. This then gives you a bitmap that shows the difference between each pair of layers a a colour. The brighter the colour the bigger the difference. Since we are actually dealing with very small values most of the time I also added a levels layer at the top of the stack just to brighten the result so that you can easily see what is going on. I added a 10 sampler points, which with the levels layer active lists both the actual pixel value, and the value after adjustment.

So with a method for analysing the results I ran the following exports from LR, and to be sure that there was no variation between instances I ran each export twice. I did my first export with no sharpening, so that I had a base to work from. I then exported with the resolution set to 100 PPI and 200 PPI and also ran Screen Low and Screen High as the sharpening. After assessing these I went back and added 72 and 300 PPI but only at Screen Low. There was zero difference between any of the pairs as you would expect, and contrary to the belief of some (including me) there was zero difference between any pixels when changing the resolution value. There was though measurable but small differences between high and low levels of sharpening. Compared with no sharpening Low gave the following stats, Mean: 0.93 SD 1.28, Median: 1 and I think maximum value was 29. None to High gave 1.66/2.22/1/51.

So I then repeated the test for printing, and I selected Glossy paper and again went with Low and High settings, although I only ran one export of each case, using the following PPI values: 72, 100, 149, 151, 240, 300. I later added 400, 600 and 1200 PPI. The results for this test were rather more interesting, with changes to the resolution having a significant effect on the sharpening. All of the output resolutions from 72 to 151 PPI all had exactly identical levels of sharpening. There were measurable differences between those and the next value, 240 PPI, and then also between 300, 400 and 600 PPI with each resolution getting a different level of sharpening. There was zero difference between 600 and 1200 PPI. So for the paper options there seems to be a band of values that result in sliding levels of sharpening.

Something that I hadn't considered was that the sharpening level went down as the resolution increased, for some unknown reason I had expected it to be the other way around, although at either level or any resolution the print sharpening was much higher than that for screen. That is assuming that the larger the difference between pixel values implies more sharpening, since it is a bigger change. I have saved the PSD files, so if anyone is interested in seeing the results ask and I'll put them up on Dropbox.

Alan


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Nov 20, 2016 15:20 |  #20

BigAl007 wrote in post #18189798 (external link)
Ok so I ran some quick tests, and here are my results. Firstly I will describe how I measured the results of the sharpening applied, I did this by simply loading all of the exported files as layers in PS and setting the blend mode to difference. This then gives you a bitmap that shows the difference between each pair of layers a a colour. The brighter the colour the bigger the difference. Since we are actually dealing with very small values most of the time I also added a levels layer at the top of the stack just to brighten the result so that you can easily see what is going on. I added a 10 sampler points, which with the levels layer active lists both the actual pixel value, and the value after adjustment.

So with a method for analysing the results I ran the following exports from LR, and to be sure that there was no variation between instances I ran each export twice. I did my first export with no sharpening, so that I had a base to work from. I then exported with the resolution set to 100 PPI and 200 PPI and also ran Screen Low and Screen High as the sharpening. After assessing these I went back and added 72 and 300 PPI but only at Screen Low. There was zero difference between any of the pairs as you would expect, and contrary to the belief of some (including me) there was zero difference between any pixels when changing the resolution value. There was though measurable but small differences between high and low levels of sharpening. Compared with no sharpening Low gave the following stats, Mean: 0.93 SD 1.28, Median: 1 and I think maximum value was 29. None to High gave 1.66/2.22/1/51.

So I then repeated the test for printing, and I selected Glossy paper and again went with Low and High settings, although I only ran one export of each case, using the following PPI values: 72, 100, 149, 151, 240, 300. I later added 400, 600 and 1200 PPI. The results for this test were rather more interesting, with changes to the resolution having a significant effect on the sharpening. All of the output resolutions from 72 to 151 PPI all had exactly identical levels of sharpening. There were measurable differences between those and the next value, 240 PPI, and then also between 300, 400 and 600 PPI with each resolution getting a different level of sharpening. There was zero difference between 600 and 1200 PPI. So for the paper options there seems to be a band of values that result in sliding levels of sharpening.

Something that I hadn't considered was that the sharpening level went down as the resolution increased, for some unknown reason I had expected it to be the other way around, although at either level or any resolution the print sharpening was much higher than that for screen. That is assuming that the larger the difference between pixel values implies more sharpening, since it is a bigger change. I have saved the PSD files, so if anyone is interested in seeing the results ask and I'll put them up on Dropbox.

Alan

Thanks, Alan. This agrees with my findings. To summarize:

Specifying different resolutions in ppi in LR when exporting makes no difference at all to the image when exporting for Screen.

Resolution does in general affect the image when exporting for Print. It changes how sharpening is implemented. However, there is no change between 600 and 1200 ppi, suggesting that the effect levels out at higher specified resolutions.


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BigAl007
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Post edited over 4 years ago by BigAl007.
     
Nov 20, 2016 18:46 |  #21

Archibald wrote in post #18189996 (external link)
Thanks, Alan. This agrees with my findings. To summarize:

Specifying different resolutions in ppi in LR when exporting makes no difference at all to the image when exporting for Screen.

Resolution does in general affect the image when exporting for Print. It changes how sharpening is implemented. However, there is no change between 600 and 1200 ppi, suggesting that the effect levels out at higher specified resolutions.

Not only does it reach a level at higher resolutions, but also at lower ones too. If I had to make a guess, without running additional tests, I would expect it to be at 600 PPI and above, and quite possibly at up to 240 PPI, since that also seems to be quite a common default setting for various cameras and software.

Alan

Oh I guess I should also have said the test was carried out using the latest LR CC 2017 release.


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