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1. Re: What algorithm is used by Export module when resizing a picture?
thedigitaldog Feb 26, 2013 10:19 AM (in response to Rafael Aviles)LR is a bit smarter than Photoshop and does all this for you automatically. It's an adaptive Bicubic interpolation. If you ask for a size up, LR knows this and if you ask for a sizing down, it knows this too and applies the appropriate algorithm automatically for you.
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2. Re: What algorithm is used by Export module when resizing a picture?
Rafael Aviles Feb 26, 2013 10:24 AM (in response to thedigitaldog)Thanks, Andrew, I thought that is what LR does. PS does a similar thing if you choose Bicubic Automatic in the Image Size panel. It knows to use "Bicubic Smoother" for a size up, and "Bicubic Smarter" for a size down. Are these the same algorithms used by LR? Or is "adaptive Bicubic", as you call it, a different algorithm? And my other question still remains - is there a way for me to choose which one is used, when the LR "smart" choice is not what I want?
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3. Re: What algorithm is used by Export module when resizing a picture?
thedigitaldog Feb 26, 2013 10:26 AM (in response to Rafael Aviles)It's not identical. For one, the processing TRC gamma in LR is quite different than in Photoshop which can vary. You cannot choose how you want LR to apply it's sizing algorithm.
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4. Re: What algorithm is used by Export module when resizing a picture?
Rafael Aviles Feb 26, 2013 11:03 AM (in response to thedigitaldog)Thank you, Andrew.
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5. Re: What algorithm is used by Export module when resizing a picture?
areohbee Feb 26, 2013 4:17 PM (in response to Rafael Aviles)Rafael Aviles wrote:
the Sharper algorithm results in over-sharpening (to my taste)
I've found the resizing in Lr to be very nicely done (not over-sharpened...) - both directions (bigger & smaller). Nevertheless, here are a few thoughts:
1. Make sure you have no output sharpening specified (sorry if this was obvious - I couldn't tell from your previous post if you were aware of it or not).
2. If still too sharp, maybe it's over-sharpened to begin with. i.e. consider sharpening more moderately in Lightroom, then *add* output sharpening if need be upon output.
3. If for some reason you just don't like the resize algorithm, you can wire up another one by way of post-process action, e.g. Lr/Mogrify, Photoshop droplet... Personally, I don't think any improvement can be had this way, but you might disagree (and that would be OK ).
Cheers,
Rob
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6. Re: What algorithm is used by Export module when resizing a picture?
Rafael Aviles Feb 26, 2013 4:40 PM (in response to areohbee)Rob, thank you very much for your suggestions.
1. Yes, I had already selected no output sharpening.
2. The pictures are not over-sharpened to begin with (at least to my eyes). The issue is that in my workflow I do a bit of selective (or creative) sharpening, beyond the capture sharpening, on the full size file as imported from the camera or the scanner. At this point, I can get prints from this file and everything is fine, I do not downsize for that. However, if I want to post the picture on a web site, or share it by email, I usually downsize it to manageable pixel dimensions (or required dimensions by the web site). This is where I thought the additional sharpening implemented by LR could lead to oversharpening.
3. I'm not sure I follow you here, but I agree that post-processing after LR has already sharpened the file during the downsizing would not lead to an improvement. Is that what you meant?
I should add that I have not done extensive testing with the LR Export module, so it may well be that, as you say, it does a nice job and it does not cause over-sharpening. I'll try it and see how it does. I was just asking the question because of my experience with Photoshop and the Bicubic Sharper choice when downsizing.
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7. Re: What algorithm is used by Export module when resizing a picture?
areohbee Feb 26, 2013 7:28 PM (in response to Rafael Aviles)Rafael Aviles wrote:
I'll try it and see how it does.
Good idea. Probably the rest is moot until then.
But in general, Lr's resizing algorithm is smooth as silk - if anything, a little soft, but there are output sharpening options for that case.
Try it! (re: #3 above: you can export at full-rez and pipe to a 3rd party resizer if desired, but perhaps we are jumping the gun here...).
Rob
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8. Re: What algorithm is used by Export module when resizing a picture?
Jeff Schewe Feb 26, 2013 9:28 PM (in response to thedigitaldog)Andrew Rodney wrote:
It's not identical. For one, the processing TRC gamma in LR is quite different than in Photoshop which can vary. You cannot choose how you want LR to apply it's sizing algorithm.
In addition to the points Andrew made, the other main difference with the LR resampling is that it's an adaptive interpolation between Bicubic and Bicubic Smoother for upsampling and Bicubic and Bicubic Sharper for downsamples. Depending on the amount of up/down sampling, LR interpolates between the 3 variants of Bicubic. That's something Photoshop can not do (yet). This is yet another vote for the LR interpolation.
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9. Re: What algorithm is used by Export module when resizing a picture?
Rafael Aviles Feb 27, 2013 6:52 AM (in response to Jeff Schewe)Jeff, thank you very much for the information, I really appreciate it.
Rob: I did a couple of side-by-side comparisons, downsizing the same pictures with Ps "Bicubic Sharper" and with Lr Export module. I do like the ones downsized by Lr better than the Ps ones. The Lr ones are very close to what I get with Ps "Bicubic Smoother" when downsizing these files. Again, my results are based on already sharpened large files (4288 px x 2848 px), downsized to 900 px x 600 px.




