To Quadruple and Beyond – OSSC Pushed to the Limit

Another month, another fantastic set of new features for the Open Source Scan Converter! New firmwares for the miracle little device are appearing at a frantic pace, giving enthusiasts plenty to get excited about. As we probably all know by now, the OSSC is a line doubler device. Rather than working on a frame at a time, the OSSC processes a single scanline at a time, meaning there’s no frame buffer and no input lag. Line doublers were more common near the start of the switch-over from CRTs to fixed resolution displays, but development of them was stopped due to a frame-buffer design being much more suited for quality deinterlacing of interlaced content. Until now, we’ve never really discovered just what would be possible with a next generation line doubler. Not so long ago we wrote about the OSSCs world first line tripling mode, but what if we could go even further than that?

Line Quadruple

If your display can handle it, line quadruple looks super sharp.

The next logical step is, of course, line quadrupling. If we can double or triple the lines, why not quadruple them? 320 x 4 = 1280 and 240 x 4 = 960. 1280 x 960 happens to be a standard PC resolution, so it looks like we’re in business. Line quadruple mode (or Line4x mode for short) was introduced in firmware version 0.76 and is now out of beta and ready for the mainstream.

As you might expect, line quadruple mode gives a wonderful sharp picture on compatible displays and is ideally suited to pixel art. Scanlines look good too, much improved from those seen while the firmware was in beta and they give the image a much more natural look. Just like line triple mode, the 1280 x 960 signal the OSSC generates in line quadruple is somewhat off-spec, meaning many monitors and especially TVs will flat out reject it. As for secondary video processors, we found the DVDO Edge Green would accept the signal and produced a great image, but the more desirable VP50 Pro would not. Capture cards may struggle with compatibility too. The Startech PEXHDCAP managed to capture just a quarter of the screen before rejecting the rest of the image, hence the small sample we were able to collect for the picture above.

Line Quintuple

The next logical step is, of course, to multiply the line by five, let’s do the maths (or math, if you’re American); 320 x 5 = 1600 and 240 x 5 = 1200. Now of course we have a problem, 1600 x 1200 does not even fit in a 1920 x 1080 image that most modern TVs use.

Line quintupling on a 1600 x 1200 display is quite something.

Of course, there are displays that have a fixed resolution of 1600 x 1200. Before the world went widescreen, a number of PC monitors were made in this resolution. If you own one of these monitors, you can use line5x mode in 1600×1200 output mode directly, resulting in a breathtakingly sharp image that fills your monitors screen completely without having to crop the image. Again, the OSSC doesn’t put out a standard 1600×1200 signal by any stretch, but computer monitors, especially older monitors tend to be more tolerant of these deviations from spec.

We had no problems displaying the line5x signal on our Samsung SyncMaster 204B, a 1600×1200 panel from back in 2006. Sadly, panels this old tend to be rather dated when compared to modern displays and no displays are made in this resolution any more, but if you did want to use a panel like this for retro gaming, there’s really no better way.

Overscan advantages

Anyone familiar with using CRTs will probably be familiar with the term “overscan”. The tendency for CRT displays to crop parts of the image at the edge of the screen. Good quality CRTs suffered from this less, but cheaper models often did it more. Because of this, few games or TV broadcasts used the edges of the image for anything of critical importance, anticipating that peoples televisions might not even display this part of the image. This bit of display history means that we could simply throw away these parts of the image, just like the old CRTs often did, and just display the inner part of the image instead. That’s exactly the approach Marqs took when developing the 1080p line5x mode.

1080p on the OSSC is now a reality

Line quintupling on the Megadrive

Ladies and gentlemen, the picture here shows real 1080p output from the OSSC, something that was thought to be impossible at one time. The game shown is the awesome Japanese shooter “Undeadline” on the Sega Megadrive. As you can see, although parts of the image are cropped, the life, score and special weapons displays are still fully visible.

Again, due to the signal being somewhat off spec, we weren’t able to use line5x mode directly on our TVs. It is however, fully compatible with both the DVDO Edge, the DVDO VP50 and the VP50 Pro. In order to get a stable image at the correct aspect ratio with our 50 Pro, we had to tweak the advanced timings on the OSSC. We found the following values worked best:-

H. Samplerate 2057

H. Backporch 255

Closeup of Line5x mode. This is a digicam shot, none of our capture hardware is compatible with this mode.

Using high quality cables fully rated for 1080p is also a must for this mode. If your HDMI cable is not up to snuff, you may simply get a “No signal” message regardless of your display. Furthermore, in our tests we found that some HDMI splitters may reject this signal, even ones normally rated for 1080p use.

Given its compatibility limitations and the fact that part of the image has to be cropped, the OSSC is still hardy a replacement for a full scaling solution like an XRGB Mini or a DVDO+OSSC combo, but then as we’ve repeated ad-nausium in the past, the OSSC was never designed to replace scalers like these. What you do get is a unique, input lag free presentation in 1080p that’s suitable for many retro game titles. That’s something you can’t get anywhere else.

The future.. OMG, Line Sextuple?!

Will there be a line sextuple mode on the OSSC? Unfortunately not, we’re now at the limits of the current hardware. To go into 4K resolutions would unfortunately require more powerful hardware. Will a more powerful OSSC arrive one day?, it’s certainly possible. For now, we can expect the rate of new firmware updates to slow down a little as the device is now close to feature complete, at least as far as Marqs imagined it.

That’s not to say the OSSC is finished as far as new features are concerned. Being open source means that skilled programmers around the world can add new features to the device. One such programmer has taken the initiative and added a custom firmware that brings scaling filters to the hardware. Filters like Scale2x aim to smooth out pixel art, making it look like more natural, hand drawn or painted imagery. It’s not for everyone and tends to work better in some games than others (particularly cartoon-like games such as Yoshi’s Island can often look very pleasing when run through these filters). If you want to experiment with this firmware, it’s available now, see this post on our forums for more information.

Who’d have thought this one little box would do so much for upscaling and converting of legacy video formats? For retro gaming enthusiasts, the OSSC is an essential part of your AV toolbox, if you’ve not got hold of one yet, be sure to put your name on our waiting list as soon as possible.


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