Talk of VMware’s Horizon View 7.3 release prompted me to take a closer look at the latest offering of their display remoting protocol, Blast. I’ve used earlier versions of Blast and found it to be very resource-hungry, especially when it comes to network bandwidth. Granted, if you spend most of your time on a LAN, bandwidth is probably not your main concern, but the thing that really stood out to me was image quality: after 15 minutes or so, I had to stop using the desktop because my head started to hurt!

It’s clear that Blast was and is still largely based on the well-established and popular H.264 codec. As video codecs go, H.264 is hard to beat. That’s why Citrix uses it for video content, as well. But as an everyday desktop remoting protocol, it really falls short of the most basic tenet of desktop remoting: image quality.

To illustrate this point, I’ve put together a simple coloured spreadsheet in Excel and compared — using out-of-the-box settings on a LAN — how HDX and Blast look vs. local:

You’d be hard-pressed to see any difference between Local and HDX. Blast, on the other hand, is very different. Here’s a close-up showing some key differences between HDX and Blast:

OK, I’ll be the first to admit that some of the colour combinations in the spreadsheet wouldn’t be my first choices, but even the highly contrasted text exhibits “ghosting” artefacts which, after a while, make it exceedingly tiring on the eyes.

Dig a little deeper with an image editor (get in touch if you want to find out how I did this), and it’s possible to exaggerate the actual pixel-level differences:

Here, black means the pixel is unchanged. You know when I said that you’d be hard-pressed to see any differences between Local and HDX? That’s because there aren’t any! By default, HDX is pixel perfect *where it matters*. Blast, on the other hand, changes almost every pixel to some approximation of its original colour.

So, putting quality aside for a moment, what about the bandwidth cost? Remember, many of our customers are on pay-per-byte schemes. Surely the pixel-perfectness of HDX comes at a cost? The raw, uncompressed byte size of that particular strip of spreadsheet is roughly 300KB. Blast gets this down to 70KB, and stays around there each time the image is shown at a later point.

HDX? 22KB. And the best part? The clever stuff in HDX means that it’s virtually free on subsequent appearances.  🙂

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