Alley in Pisa, Italy

by Lars Kotthoff

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I am doing various export tests to get nice looking thumbnails for my photoapps. My thumbs are 120 x 80. So far the output sharpening from Lightroom looks the best, (sharpen for Screen, High) only problem is the filesize… I can't get them under 25KB. My ideal filesize would be 10-12KB. When I set the "Limit File Size To" to these numbers LR just does not care and goes again over 25KB. Using a low quality number (like 40) and again 25KB very badly compressed.

Photoshop's "Save for the Web" gives me the desired filesizes, but I can't get the sharpening good looking like LightRooms. In photoshop I resize to 120 x 80 (bicubic sharpener) and do > unsharp mask, amount 50%, Radius 1.0, Threshold 0 Obviously using these defaults is not the best way to go. I think I remember something about smart sharpening or high pass sharpening?

So I wanted to know what are the best sharpening techniques in PS to get great looking thumbnails? Cheers

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2  
One thing about compression is that it tends to remove fine details while good sharpness requires, so you are fighting one with the other :) –  Itai Nov 15 '10 at 16:08

3 Answers 3

I find LR's output sharpening better than any techniques and settings I tried from PS:

  • various unsharp mask settings (including the 2 mentioned here)
  • sharpen > fade sharpen
  • high pass sharpening
  • Photokit's Output Sharpening

Nothing beats my LR output sharpening with "Sharpen for Screen High"

I have found out how to get them small.

  • Update LR to 3.2, this will improve LR's "Limit File Size To".
    I used 20KB as target.
  • The last thing was quite a surprise for me.
    In LR I selected "Minimize Metadata" about the same as PS' > save for web > oprimized setting. LR seems to minimize.. not so minimal.
    So I had a look with Exiftool and there was still a bunch of metadata. When I deleted all metadata with Exiftool I shaved of 10KB!
    Off course by doing this command you will deleted also your ICC profile, copyrights etc, but you can also delete or add anything you want. A command line I use (and converted into an service on OSX, so it's accessible from finder's context menu) is:

_

/* delete all exit data except for the ICC Profile, add copyright, overwrite the original */
exiftool -all= --icc_profile:all -copyright='your copyright, name, website ect. here' -overwrite_original newfile.jpg

All images resized from 3000x2000 to 120x80 in Photoshop > Save for the Web, quality 75, optimized

No Sharpening: (12KB)

Unsharp Mask, amount 300%, radius 0.2, threshold 0 (16KB)

Sharpen > Fade 50% (16KB)

Highpass technique (16KB)

and finally LR + exiftool (8KB)
LR, limit file size: 20KB, sharpen for screen High

Look at the blue stripe above the waterline, the greens, the diagonal lines running up the mast.

Just for reference I have a higher res of the example.

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There are many sharpening techniques (google high pass filter, octave sharpening) as well as specialist tools, e.g.smart sharpen, and third party plugins e.g. SharpenerPro

Most of these are overkill for thumbnails. I find unsharp mask does the job. When downsizing an image you end up with a lot of fine detail so you can use a very small radius and get good results. This also minimises "halo" effects which is a good thing when your images are small.

The settings I use are radius 0.2, strength 300, threshold 0

There's always a sharpness/filesize tradeoff with JPEG files as storing higher frequencies requires more space. You can reduce the strength value to reduce the filesize. Alternatively you can mask the thumbnail so the centre is sharper than the edges (assuming most of the important detail is toward the edges).

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I just did some more tests and I don't see any difference with amount 50%, Radius 1.0, Threshold 0 and amount 300, Radius 0.2, Threshold 0. I pixelpeeped also smart sharpen and another one that does > sharpen > fade sharpen 50%, but al these do not look as good as LR's output, they all tend to bump up the blacks. –  FFish Nov 15 '10 at 18:17
    
I don't have Lightroom but if you could post a couple of the Lightroom thumbs along with the original images I could have a go a replicating what LR does in Photoshop. –  Matt Grum Nov 17 '10 at 10:23
    
posted! also a link to a large photo on Flickr. Looking forward to your output. Thanks Matt. –  FFish Nov 18 '10 at 8:41

I create the images for my website (guffa.com) in Photoshop. My thumbnails are 100 x 67 and most of them are between 4 and 6 kB.

I resize them using bicubic, then use unsharp mask with settings:

  • amount: 50%
  • radius: 0.5
  • threshold: 2

Then I save them using Save For Web as JPEG with quality setting 60.

The radius is based on an average screen resolution of 100 PPI.

Some examples:
Trees Factory Cobble stones Bridge

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