Author Topic: Interpolation/JPEG options used for Web Page Wizard thumbnails vs. batch mode  (Read 2607 times)

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I'm trying to figure out what specific interpolation options, JPEG compression parameters, etc. are used by the Web Page Wizard (Alt+F9) to generate thumbnails. What I'd like to be able to do is set up Batch Process to produce the same images, but so far the specific way Web Page Wizard creates them under the hood eludes me.

This is what I'm setting in the Web Page Wizard - that's all I *can* set as far as JPEG options go. No way to select downsampling interpolation or anything, only size and quality:

This is what I'm using for batch mode:

Source image is a TIFF.

The files end up having the same size in pixels, same basic metadata (quality, resolution, JPEG sampling factor, colorspace, whatever else ImageMagick's "idenfity -verbose" spews out), but they're not the same size in bytes and the resulting image is different, visibly so in some cases. Now, I tried changing interpolation and sub-sampling for batch mode, but it doesn't look like I'm getting the same result anyhow.

Now, you're probably asking "why would anyone want to be that particular about this?" and the answer is, the results we've been getting from the Web Page Wizard's thumbnail generation are so good and reliable for the specific types of images we handle that it's still in use over here long after server-side software became capable of generating its own thumbnails and we stopped actually using the generated webpages themselves - however, this approach is becoming increasingly unwieldy and impractical, for a multitude of reasons you can probably guess yourself. Thus, I've been trying to re-create the Web Page Wizard results in Batch Mode, under the assumption that this is what's actually being used under the hood.

The next step would be to either use Python scripting to integrate that batch flow with an automatic upload to a server - or to use the known set of batch mode options to further re-create the result with ImageMagick, which can be then integrated into server-side software and finally get automatic thumbnails that are not crap within the online store itself.

So, what's the exact magic behind Web Page Wizard's thumbnails? Anyone?

Daan van Rooijen

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I don't know the secret recipe either, but the regular thumbnail settings (under Options | Preferences) allow you to choose sharpening and contrast enhancement, so maybe those come into play here as well.

Have you tried if Thumbnail | Export to JPG gives you images of a similar quality?

The Viewer/Editor has an auto-enhancement function in its Image menu that's cryptically named Xe847. One thing that it does is turn anything blueish into a sunny sky blue. Once you know that, it's easy to tell which images have been treated with it. Another possibility could be Histogram stretching.

If you could post a few representative sample images that show the original and web-thumbnailed images for comparison (at the same size), maybe those will offer further clues as to what's happening under the hood.
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