One photo in Lightroom exporting extremely pixelated despite high file size

[eabrahams]

Version: LR Classic 12.0

Mac: Ventura 13.0

Today I did a photoshoot. I imported the photos to Lightroom, edited one, took it into Photoshop and followed my normal process, including adding 3 overlay layers. Please assume I know what I'm doing in both programs and this follows a VERY NORMAL routine for me. 

I saved the photo and returned to Lightroom, where the photo looks as expected. I might attach a screenshot.

I then exported the photo using an export preset that I use daily. The preset settings have not changed. 

The photos usually export at 2048 px on the long side, with the file size limited to 2mb, resulting in them usually being about 1mb once exported.

Upon checking this one particular photo, it has exported at extreme potato quality. It's got huge square pixels. I'll attach it. It is also 6mb in size.

Here's what I've done to troubleshoot:

• Merge/stamp all layers in PS, save and export again. No change.
• Rasterise overlay layers, save, export again, no change.
• Export without file size limitation: great quality, 11mb. I can't be exporting my photos this large. FB will kill me. 
• Export the RAW file to jpeg from LR (without PS edits): looks fine.
• Export a photo from LR from a different photoshoot day using the same export preset: everything normal and expected.
• Export the same photo as above with all layers from the cursed photo using the export preset: everything normal and as expected.
• Export a different photo from today's photoshoot WITH ALL LAYERS including the original image layers as smart objects on top, using the export preset: everything fine and normal.

I have thoroughly checked the export preset settings. They are the same as they always are.

I have tested with two different photos; one from 3 days ago, one from today. I have tested those differnt photos with all the layers and adjustment layers from the cursed photo, so the .tif file size is the same as the cursed photo, the pixels are the same, everything is the same..

So what I'm wondering is why I have one cursed photo? Maybe I'll have more in the future, which will be extremely frustrating because I have to then export it some other way, or have a massive file size, or just copy all the layers on top of another photo and save it back to LR and export it that way 😑

[Rob_Cullen]

I cannot see any blockiness in the "Cursed photo exported" on my screen at 90%

[eabrahams]

That's because that file is "cursed photo exported without limitation". 

take a look at "cursed photo 1"

[SeanMcCormack]

I can see the blockiness in the preview vs the unlimited version. I imagine what's happening is the amount of graduation in the photo means that JPG compression isnt as efficient as with areas of continous tone. Forcing it to a lower size is creating artefacts as it simply needs to use more space than you're allowing. Is it odd that it needs this? A bit. But if it needs to be that large a file in this days of fast internet and cheap storage, why worry? It could also be a result of how Lightroom chooses to remove the required space. It may in fact just be doing a terrible job of it. Experiment with forcing your average photos into 500kb.. if they look as bad, you know it's ineffeciency in the compression being applied. 

[Jao vdL]

Agree with Sean, these are jpeg compression artefacts caused by it being forced into very low quality mode but there is a secondary effect here. You can learn more about the effect of jpeg compression here: http://regex.info/blog/lightroom-goodies/jpeg-quality 

I experimented a bit with your file using the unconstrained image and reexporting from that at 2048 pixels and every image comes out bigger than 5 MB even at quality setting 10% which is incredibly low. I then selected to export with only copyright for the metadata and it immediately was only a few 100kB and as fine quality. What is happening here is that you have a gigantic chunk of metadata embedded in your image somehow and the size limiting algorithm is getting tripped up by the many megabytes of random embedded metadata that it is writing into the jpeg output. I took a look at the metadata and there is a gigantic block of crazy random xmp metadata in there of type photoshop:DocumentAncestors. Which is crazy. In fact Photoshop won't even display the metadata on this file as it is too large. So yeah export this one file using the copyright only setting. Something happened to this file that generated all this random metadata and I have no clue (probably a bug in photoshop) what that was but this is the cause of your problem and also explains why it only affects this one image.

[eabrahams]

Thank you for your thorough investigation. I know about image compression but there was no explanation for why this was occurring just for this one specific photo... except for this metadata that you found. Because the .tif file sizes were the same, there was no way to explain what was going on. 

Appreciate your help. Hopefully it's just a weird bug in PS. I'll export without metadata on this image.