Thanks for A very enjoyable and informative read. It seems that I am the only one who uses a different export method. I leave the LR quality setting at 100 but choose a “limit file size to x”. Typically this will change my 10MB NEF images to 512K (or 2048 if I think someone will want to print up to 5×7) Is there a flaw in my method?

Ian

Assuming that you always choose the proper ‘x’ for the output-pixel size you select, it seems fine except that exports will take longer as Lightroom iterates over the qualities until it finds one that fits. At least, I assume that’s how it would work. —Jeffrey

The only thing I can think of that would account for that 150k is just an inordinate amount of Lightroom/ACR specific metadata. I guess I always just assumed if it wasn’t filled in/adjusted, it didn’t get written to the metadata. But looking at the normal export without everything stripped in your exif viewer there was a massive amount of data, and the majority of it was blank.

I’m still curious where the extra 18k came from with just removing the Lightroom metadata, though. The file was 57k, so if the thumbnail was 18k and the profile 3k, that still leaves about 13-15k unaccounted for over the Save for Web (or now metadata wrangled) 22k export.

There’s quite a bit of difference between the quality levels, and those of save-for-web and Lightroom don’t correspond, so that could easily explain the difference. Try save-for-web at 10% higher quality, and perhaps it’ll match up with Lightroom. —Jeffrey

From your exif viewer, it looks like Save for Web strips the exif data, which appears to be taking up 18k in the export from Lightroom (although I thought “Minimize Metadata” was supposed to strip that? The data itself is gone, but the exif viewer is showing a block for exif that is encoded in 18k)

EXIF — this group of metadata is encoded in 18,773 bytes (18.3k)
Compression JPEG (old-style)
Resolution 72 pixels/inch
Thumbnail Length 18,613

That doesn’t appear on the Save for Web version.

The rest appears to be coming from the embedded thumbnail that’s 18k, and not present in the Save for Web version. That seems kind of pointless to embed a jpeg thumbnail…in a jpeg. I don’t see anything in Lightroom’s export dialog to disable that thumbnail embedding… Looks like I need to check out your Metadata Wrangler plug-in

… Yep! That did it. Got it down to 22k out of Lightroom by basically stripping all metadata except the ICC profile and copyright/creator info. Once again, you are a life saver, and a genius

I’m curious what was taking up so much space. If the thumbnail was taking 18k (the thumbnail is part of the Exif data, which is why it’s there even when “Minimize Metadata” is enabled) and the profile 3k, what’s accounting for the 150k that got stripped? Something doesn’t sound right. —Jeffrey

This appears to be a bug when you export small image dimensions, causing the file size to explode.

As Jeffrey mentions, this is almost certainly image metadata that is accounting for most of the file size. Embedding an ICC profile means the entire profile itself is added to the JPEG itself. I’ve seen print profiles exceeding a megabyte in size, which means every JPEG will have over 1024K added to it, even if it is a 1×1 image. Tagging an image with the output profile only embeds the name of the profile, with the assumption whoever you are sending it to already has the profile on their system.

Another culprit is an embedded thumbnail. Those can be hundreds of kilobytes in size, or larger. It makes sense if you are sending a print-ready, 24-megapixel image. A small 200K preview image is just fine for viewing. But if your image is only 50K to begin with, it doesn’t make sense to include a preview at all! I don’t think Lightroom is doing this, so I also think the problem is caused by an embedded profile.

FYI, Lightroom scales the size of the embedded thumbnail. I don’t know whether it ever actually omits it, but the thumbnail size seems to be based on some percent of the image size, so a tiny image gets an even tinier thumbnail. —Jeffrey

One example I exported an image at 250px on the long edge, 60 quality, standard screen sharpening. This produced an image 250px x 167px that came out to 210k. Needless to say I was kind of shocked to see that, particularly because it’s such a small pixel dimension image, there are fewer than 42,000 actual pixels, so that’s almost 5 bytes per pixel which seems quite high to me. Curious what a quality of 100 would produce, I exported it again and it only climbed to 250k file size… not the vast difference I was expecting.

Next, using “Edit In” in Lightroom, I brought the NEF into Photoshop and used “Save for Web and Devices” with the default Jpeg High settings (60 quality), and having it resize to 250px wide.

I don’t know what kind of secret sauce it’s using, but going through Save for Web produced a file size of 20k. And after some pixel peeping (what little can be done with a 250×167 image) the two images look identical to me.

For grins, I went back to Lightroom, and tried to enable the “Limit File Size To” option, to limit it to 20k, and see if that might switch to something more like the Save for Web compression mojo. It mocked me with an error saying it couldn’t produce an output that small.

So I wanted to see what size Lightroom would produce an uncompressed 8bit TIFF. If my math is correct, the calculation should be w*h*total bit depth/8, or 250*167*24/8 = 125,250… however the TIFF Lightroom produced is 353k. WTF Lightroom?!

This appears to be a bug when you export small image dimensions, causing the file size to explode. Exporting the same image at 800 on the long edge, but otherwise the same 60 quality, standard screen sharpening produced an image that was 800×536 and 289k. With 428,800 pixels that makes it about 2/3byte per pixel. That’s two thirds, not 2-3. Much more in line with what I would expect from just slightly over mid-range quality level.

I tried one last test, 250 long edge, standard screen sharpening, quality 0. The resulting file size is 201k, but visually it looks a bit like an impressionist painting.

… this is me tossing my hands up in frustration.

I never noticed this problem before because on my site and Flickr or Picasa, I always export much larger images (960px on my website, and 1024-1200px to photo sites).

Makes me wish there was an easy way to batch Save for Web. When I’ve got a gallery of ~100 client images I need to export, I like being able to do so in Lightroom and get up and get some coffee or whatever. Batching Save for Web either produces one file, as it uses the last file name provided and thus overwrites the image over and over again until it gets to the last image in the batch, or you have to babysit the save dialog to provide a new file name for each image. Ugh!

I haven’t delved into droplets yet, though I found a tutorial that’s suggesting droplets are the way to go for batch Save for Web. Must try this out! If it works, I guess I wouldn’t mind exporting thumbnails and other small images from Lightroom at 100 quality, then dropping them on a Photoshop droplet to batch Save for Web at 50-60 quality.

Besides the image there’s also image metadata, and that always includes an embedded color profile. Are you by chance exporting with a huge custom color profile?
Perhaps check out the 250px version for hints in my exif viewer, or email a copy and I’ll take a look. —Jeffrey

—
eok

Ps.: in the Uber Challenging image, I see that the quality decreases from (47..53) to (54..61). I don’t know if the images may be inverted or if it’s a trick of the gradient and the JPEG algorithm.

If I recall correctly, there’s a time when the algorithm shifts modes, and that’s likely where it’s happening, in a way that does not compliment that image. —Jeffrey

Thanks for all your great stuff.
-Clifford