Lightroom JPG export - resizing algorithm different than preview image in Develop mode?

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It looks like the Lightroom JPG export functionality uses a different resizing algorithm than the one used to preview the image in Develop. After doing some testing using photoshop to resize the image instead (I exported the full resolution image from LR), I found that resizing using the "bicubic" algorithm matches the exported resized LR image, while using the "bilinear" algorithm matches the image in the Develop preview screen. Of course as you make all your adjustments in Develop, you would want the exported image to be a perfect match to what you worked on.
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LPChiasson

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Posted 6 years ago

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jdv, Champion

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" Of course as you make all your adjustments in Develop, you would want the exported image to be a perfect match to what you worked on."

This does not follow. There is no way a rendition will ever match perfectly. Making renditions is exporting for certain uses, be it print or display in whatever context. The develop module is intended to be a reasonably true representation of the data for the display you are using.

It is not given that you will be making renditions to match your display. Generally, you make renditions for specific uses.
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Dorin Nicolaescu-Musteață, Champion

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But what's the real problem?

Can you show any examples where resampling algorithms result in suboptimal output?
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LPChiasson

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Sorry forgot to mention, intended for display, not print. In this case I would expect the exported jpeg to be an exact (or almost) match to what I see on screen. I know that LR does color management right, so that's not the problem. I read a lot on color profile problems that people had, and my problem didn't seem to be the same.

So when I export a photo in LR and downsize it (for example 6000x4000 down to 1200x800), the end result has noise added to it (especially in highly processed photos) and the contrast and color are off a bit (compared to what I see in the Develop preview window.)

When I export that same photo without downsizing it, and then bring it into PS and resize it using the "bilinear" algorithm, it makes a perfect match to what I see in Develop. On the other hand, if I choose the "bicubic" algorithm in PS to resize, it matches perfectly LR's resized exported photo.

Does anyone know what's the algorithm that LR uses to resize?

I'll try to make a few examples to show this.
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Dorin Nicolaescu-Musteață, Champion

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