Archive | March, 2017

Google open-sources extreme JPEG compression

18 Mar

I previously criticised JPEGmini, a commercial program that promised to reduce JPEG size by focusing on the way humans perceive colour. My repeated finding in using the program was that it was unable to provide better compression than GIMP’s JPEG export – and GIMP is free!

Now Google has fielded Guetzli, a new JPEG compression engine that Google describes as drawing on psychovisual research. So in that aspect, it doesn’t sound much different from JPEGmini. It is, however, open-sourced, and according to Google, promises 35% smaller files compared to the open source JPEG library libjpeg, which without much doubt must be the engine used by GIMP.


Original on the left, libjpeg, center, and Guetzli on the right. Google notes the paucity of blocky artefacts in the Guetzli output, but I would also note the loss in vibrance, a typical approach in noise reduction.

Guetzli, like other recent advances in imaging, is slow. So slow, in fact, that it sounds like its use case is currently limited to very frequently downloaded items like website banners, where spending a lot of time optimizing will considerably reduce traffic.

Alternatively, though, Google could put its weight behind FLIF, supporting it in Chrome/Chromium and thereby putting pressure on other browsers to also support it. FLIF promises to provide current-best lossless compression and is interlaceable – and open source.

Guetzli might give a smaller file than FLIF, but only with more lossy compression, and it sounds like it’s currently a lot slower (I have seen no figures comparing the two).

From photographers’ perspectives, Guetzli may have one further use case. Images with such highly optimised compression are unlikely to be very usable for further editing, so for showing off your work on the web while spoiling the fun for potential thieves, Guetzli or any higher-compression tool might be a good choice (but remember – Google can “guesstimate” the image back with RAISR).

Pentax KP vs. Nikon D500: white balance

16 Mar

Continuing my series on the Pentax KP, and possibly starting a sub-series comparing the Nikon D500 against it, today my attention was drawn to ephotozine’s Pentax KP sample photos, particularly the colour section:


Pentax KP (top) vs. Nikon D500 – ISO 200 (left) to ISO 819,200.

Particularly the ISO 819,200 sample from Nikon seems to be soaked in yellow, although the ISO 409,600 sample also seems affected. Here’s the 819,200 comparison, with two attempts to fix the Nikon’s white balance in post:

Screen Shot 2017-03-16 at 00.21.40

Pentax KP (left) vs. Nikon D500 OOC, Nikon D500 with my own special WB procedure, and finally Nikon D500 after “color->auto->white balance” from Gimp

If “fluorescent” white balance is used in the Pentax, it gets even further ahead of the Nikon – an unfair comparison perhaps, but it’s only a single step of configuration and straight out of camera:

Screen Shot 2017-03-16 at 00.05.09.png

With even more prodding, I eventually got the Nikon image to behave. I managed to keep noise levels on par, but keep in mind that it’s a fair amount of work, and you really have to know what you’re doing in Photoshop or Gimp to get this kind of result – remember the one button fix is the image on the far right, and it improves things, but doesn’t really “fix” the problem. Cutting to the chase, here’s that final result:

Screen Shot 2017-03-16 at 00.48.24

Even using the Pentax’ default white balance, it does impressively well, keeping in mind we had to massage the Nikon image for several minutes to get it into decent shape:

Screen Shot 2017-03-16 at 00.52.50

The bottom line is that in terms of colour, the Pentax produces reasonable JPEG output even at very high ISO, while the Nikon D500 takes considerable time in post-processing to achieve a competitive result. The Nikon is not usable as a JPEG camera at this high ISO and I would instead recommend, if using the D500 at all, to shoot raw and use a raw converter, in which case it’s the raw converter’s job to give you a reasonable-looking image (this will be the next part in this series, if time allows).

Pentax’ PLM and DC lenses explained

2 Mar

DC (“direct current”) is a kind of focus motor that has been used in Pentax lenses for some time. While it is quiet, it’s not entirely silent. Pentax’ most recent 55-300mm lens features a new type of motor branded as PLM. Here is what Pentax representatives had to say about it in an interview:

The PLM design can quickly activate and allow for faster focusing, but the lens element must be low weight due to limited power (torque).

The DC motor can generate high power (torque) with deceleration mechanisms, which is better for lenses with larger focusing elements. A DC motor can be driven at high speed, but there is an issue that a little sound is generated.

Generally, we use the what we feel is the best focusing mechanism for each specific lens design.

It would be reasonable to suspect that the 55-300mm’s new optical formula and narrower aperture were needed to allow the faster, silent motor to be used, although it should be noted that, like the recent 18-50mm kit and non-kit zoom lenses, the new 55-300mm lens is collapsible to a somewhat smaller size, with the difference between collapsed and uncollapsed size being more pronounced in the 18-50mm.

In the interview, the representatives went on to explain that they do not expect to see PLM in a large aperture lens any time soon, instead putting their money on researching other kinds of motors as well as algorithms to improve autofocus.