WebP and SVG

Using WebP coded images inside SVG containers works. I haven’t found any automatic way to do it, but it is easy enough manually and results in very efficiently coded images that work well on the internets. The manual process is to Base64 encode the WebP image and then open the .svg file in a text editor and replace the

xlink:href="data:image/png;base64, ..."

with

xlink:href="data:image/webp;base64,..."

(“…” means the appropriate data, obviously).

Back in about 2010 Google released the spec for WebP, an image compression format that provides a roughly 2-4x coding efficiency over the venerable JPEG (vintage 1974), derived from the VP8 CODEC they bought from ON2. VP8 is a contemporary of and technical equivalent to H.264 and was developed during a rush of innovation to replace the aging MPEG-II standard that included Theora and Dirac. Both VP8 and H.264 CODECs are encumbered by patents, but Google granted an irrevocable license to all patents, making it “open,” while H.264s patents compel licensing from MPEG-LA. One would think this would tend to make VP8 (and the WEBM container) a global standard, but Apple refused to give Google the win and there’s still no native support in Apple products.

A small aside on video and still coding techniques.

All modern “lossy” (throwing some data away like .mp3, as opposed to “lossless” meaning the original can be reconstructed exactly, as in .flac) CODECs are founded on either Discrete Cosine Transform (DCT) or Wavelet (DWT) encoding of “blocks” of image data. There are far more detailed write ups online that explain the process in detail, but the basic concept is to divide an image into small tiles of data then apply a mathematical function that converts that data into a form which sorts the information from least human-perceptible to most human-perceptible and sets some threshold for throwing away the least important data while leaving the bits that are most important to human perception.

Wavelets are promising, but never really took off, as in JPEG2000 and Dirac (which was developed by the BBC). It is a fairly safe bet that any video or still image you see is DCT coded thanks to Nasir Ahmed, T. Natarajan and K. R. Rao. The differences between 1993’s MPEG-1 and 2013’s H.265 are largely around how the data that is perceptually important is encoded in each still (intra-frame coding) and some very important innovations in inter-frame coding that aren’t relevant to still images.

It is the application of these clever intra-frame perceptual data compression techniques that is most relevant to the coding efficiency difference between JPEG and WebP.

Back to the good stuff…

Way back in 2010 Google experimented with the VP8 intra-coding techniques to develop WebP, a still image CODEC that had to have two core features:

• better coding efficiency than JPEG,
• ability to handle transparency like .png or .tiff.

This could be the one standard image coding technique to rule them all – from icons to gigapixel images, all the necessary features and many times better coding efficiency than the rest. Who wouldn’t love that?

Apple.

Of course it was Apple. Can’t let Google have the win. But, finally, with Safari 14 (June 22, 2020 – a decade late!) iOS users can finally see WebP images and websites don’t need crazy auto-detect 1974 tech substitution tricks. Good job Apple!

It may not be a coincidence that Apple has just released their own still image format based on the intra-frame coding magic of H.265, .heif and maybe they thought it might be a good idea to suddenly pretend to be an open player rather than a walled-garden-screw-you lest iOS insta-users wall themselves off from the 90% of the world that isn’t willing to pay double to pose with a fashionable icon in their hands. Not surprisingly, .heic, based on H.265 developments is meaningfully more efficient than WebP based on VP8/H.264 era techniques, but as it took WebP 10 years to become a usable web standard, I wouldn’t count on .heic having universal support soon.

Oh well. In the mean time, VP8 gave way to VP9 then to VP10, which has now AV1, arguably a generation ahead of HEVC/H.265. There’s no hardware decode (yet, as of end of 2020) but all the big players are behind it, so I expect 2021 devices will and GPU decode will come in 2021. By then, expect VVC (H.266) to be replacing HEVC (H.265) with a ~35% coding efficiency improvement.

Along with AV1’s intra/inter-frame coding advance, the intra-frame techniques are useful for a still format called AVIF, basically AVIF is to AV1 (“VP11”) what WEBP is to VP8 and HEIF is to HEVC. So far (Dec 2020) only Chrome and Opera support AVIF images.

Then, of course, there’s JPEG XL on the way. For now, the most broadly supported post-JPEG image codec is WEBP.

SVG support in browsers is a much older thing – Apple embraced it early (SVG was not developed by Google so….) and basically everything but IE has full support (IE… the tool you use to download a real browser). So if we have SVG and WebP, why not both together?

Oddly I can’t find support for this in any of the tools I use, but as noted at the open, it is pretty easy. The workflow I use is to:

• generate a graphic in GIMP or Photoshop or whatever and save as .png or .jpg as appropriate to the image content with little compression (high image quality)
• Combine that with graphics in Inkscape.
• If the graphics include type, convert the type to SVG paths to avoid font availability problems or having to download a font file before rendering the text or having it render randomly.
• Save the file (as .svg, the native format of Inkscape)
• Convert the image file to WebP with a reasonable tool like Nomacs or Ifranview.
• Base64 encode the image file, either with base64 # base64 infile.webp > outfile.webp.b64 or with this convenient site
• If you use the command line option the prefix to the data is “data:image/webp;base64,“
• Replace the … on the appropriate xlink:href="...." with the new data using a text editor like Atom (RIP).
• Drop the file on a browser page to see if it works.

WordPress blocks .svg uploads without a plugin, so you need one

The picture is 101.9kB and tolerates zoom quite well. (give it a try, click and zoom on the image).