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Forum: Digital Processing, Software, and Printing 11-27-2016, 09:31 PM  
LR - best export practices for web/social media
Posted By southlander
Replies: 13
Views: 1,401
Several matters are at play here.


The best display quality of an image intended for viewing via an Internet browsing session is one that is exported at the resolution that it will subsequently be displayed at in the browser window of your 'average viewer', and with output sharpening being applied at this final resolution ie it will ideally be rendered 1:1 pixel for pixel to avoid on the fly rescaling and quality losses that come from that.


So the first problem is what resolution with the average viewer see the image. And sadly you have already lost control of this:


(1) users use various devices with different screen resolutions Think cheap low res phones through to high end screens hooked to pcs or iMacs. So a viewer's browser will be rendering the photo at different resolutions to address display differences.


(2) the user may set their browser to a zoom level other than 100% again introducing rescaling quality losses.


(3) as the OP notes, Facebook, Google Photos and all make their own decisions regarding what resolution they send the image down to the browser and this can be dynamic so no set 'rules' can be assumed. It is also getting harder to control the resolution of images stored in these sort of apps that are embedded in pages elsewhere eg this forum due to unfriendly revisions to the embedding code for some of these sites (I'm looking at you Google!).


You do have a bit more control if you host your own photo blog as you will come to know the standard image sizes blogs like Wordpress like to use. Provided your resolution selection suits your chosen blog theme and the resultant standard page is no more than the width of the lowest likely common deminator of screen resolutions for your viewing community, you have some reasonable chance of getting the photo rendered pixel for pixel provided the user is not zooming at other than 100%.


If your viewers use device apps rather than browsers to view your photos eg Facebook, Instagram phone apps, you'll need to do you own research on what size images they like to deal with. But unfortunately one size fits all may be elusive.


If the viewer can click through on an image to bring up the image at original resolution, then unless you want the user to be scrolling about to view the image, limit the original to the resolution of the average display you expect users to have, agian whatever that may be!


So , with the above in mind, the next decisions are technical.


(1) sharpen the final image you will be uploading to the net. If using LR's export function, you have two main sharpening options should you export at other than original image size: screen or printing, and amount. Print sharpening is the more aggressive of the two as printing needs a sharper file to start with. Then low, medium or high amounts of sharpening is available under either the screen or printing option. Output sharpening is needed as the process of down-resolving your images for the net re-introduces edge blur as the rescaling tries to align what might have been sharp edges in the full res image to a lot fewer pixels. The Export output sharpening option seeks to address this. If you don't like the export module's sharpening, export without output sharpening, then re-import the lower res file to LR (or other software), manually sharpen to taste, then re-export with unchanged resolution and again output sharpening off. This is more work that I can be bothered with, so my files are typically exported with output sharpening set to screen/medium. For some reason, the print module of LR (which I used for a while to add borders for my net destined photos) in my view renders a noticably poorer image IMO and I now avoid it and just use the Export function.

(2) Export image quality. There is no need to max out the quality setting on the LR export function. LR's export quality settings are a bit weird and do not align at all with the Jpeg quality parameter you can see in file EXIF data. This article summarises it very well: Jeffrey Friedl's Blog An Analysis of Lightroom JPEG Export Quality Settings Basically, a LR Export quality setting of 70 produces perfectly good rendering for most circumstances and with reasonable file size. At this quality setting, the JPEG quality parameter in the EXIF data reports in the 90-95 range which is pretty good. Pushing the LR quaility setting much past 70 just produces an explosion in file size for very little practical gain for online viewing. I might go to a high quality setting for a file intended for a large print but that is another topic.


So what do I do?


For images intended for my blog, I export 1200 pixels on the long edge as I have made the assumption for better or worse that viewers will be at home and probably have a screen at least 1380 pixels wide so the browser won't be down scaling a 1200 pixel image, and I have selected a theme and removed margins so I know the Wordpress page will be a bit over 1200 pixels wide and will fit the image. Wordpress doesn't default render at this resolution but a BB code tweak fixes that.


For this forum I export at 1240 pixels or whatever the forum photo albums maximum size is, so preventing the forum photo uploader re-rendering the photos to a different resolution.


For my personal use, my home editing screen and my phone I have both standardised on 2560 pixles width so I export personal viewing images at that resolution. These images are uploaded to Google Photos and downloaded and stored locally at 2560 pixel resolution to the phone and also an Ipad using a couple of third party apps. Ok, for the Ipad this isn't 1:1 but the iPad rescales 2560 pixels to 2048 pixles with good results.


The common factor through the above: output sharpening set to screen/medium (high is also mostly ok) and jpeg quality is set to 70.


Edit: Oh, and as others have commented, always use sRBG for images intended for the Internet. Many devices and apps are not colour space aware and simply assume sRBG. Anything else will not be correctly rendered.


Simple topic really, isn't it? Gotta love the 'net!
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