Screenshot Quality



2006 DVD

2010 DVD

The most difficult pictures to take with the camera have always been screenshots. Screen images are a very important part of BeebMaster and I am very rarely happy with the images produced by the camera. The results are variable in the extreme and some of the pictures I have had to settle for have been downright poor.

I had tried ways of recording the output from the BBC micro, originally onto video recorder, to capture images to use as screenshots. I never got this to work. Using the UHF output on the Beeb produced a very unsatisfactory picture, the composite video output was black-and-white only, and using an RGB-to-SCART lead would not work either. For technical reasons which were beyond me, a video recorder or DVD recorder didn't seem to be able to pick up the RGB signal produced by the BBC when it's fed in via SCART.

In November 2006, I started using a DVD recorder to capture screenshots from BBC micros using the Composite Video output. Although by default it is monochrome, it is very easy to add colour to the Comp Video signal, which has allowed me to produce high quality screenshots using this method.

There's much more on how to turn the monochrome Composite Video into full colour here.

The general procedure was to connect up the Beeb in question to the DVD recorder video the Composite Video. I use the recorder's High Quality Setting, which can fit about an hour of recording on a DVD. I initially used two re-writable DVDs alternately for doing the recordings, although this has now expanded to four. These are erased and re-used once I have finished with them, although I keep the captured video files.

For each picture I want to capture, I usually record for about three seconds, pause, set up the next picture, and record again. For "live action" activity, such as a utility or game running, I would normally run the sequence two or three times and record it each time to get the best chance of capturing everything I need.

Once the recording is done, I copy raw video files from the DVD onto my PC and then wipe the DVD for re-use.

Before using Ubuntu, I used to have to trawl my way through the video, pressing pause every time I wanted a screenshot, using the save screenshot function, typing in a file name, checking the saved file was the frame I wanted and not the one before or the one after, and then carrying on to the next picture.

Linux has a very handy function called "ffmpeg" which can be used from the command terminal. It is for converting video files between different formats, but also allows a video file to be converted to jpg, in other words, extracting the frames from the video. It will extract every single frame, which becomes rather unwieldy, but also allows extraction of frames at a specific time interval, so I use it to create frames at intervals of 1.5 seconds, which is ample for what I need.

The end result is a set of images which I can then look through and choose the ones I want to use on my website. From this point on, the method is the same as for making the picture sets from digital camera photographs. The frames are extracted at a size of 768x572 for the 2006 DVD recorder, so I leave them at this size. There is no need to crop or rescale them, so I use Phatch to suffix them and take the quality to 70%, and then to make the preview size images.

Sometimes it isn't convenient to connect the DVD recorder to the actual machine I want to capture, for reasons of space. To see what's going on, I have to have a monitor connected to the DVD recorder and there isn't always room to put the recorder and monitor right as close to the machine being captured as the lengths of cable and availability of sockets will allow.

It can also be a bit of a fiddly job to try to fit the little colour composite capacitor to a machine that doesn't have it already, especially if it's one of my machines in a permanent installation and not just a demonstration setup.

Luckily, that's where my Econet comes in, because I can use the *VIEW command to view the station I need to capture on a machine located some distance away with the colour modification applied and enough space to connect everything together and record the VIEWed screen.

Using this method in 2009, I was able to obtain masses of screenshots from my Master Compacts, in colour, even though the Compact doesn't support the colour addition to its composite video signal. I even wrote my own version of *VIEW, which updated in real-time. This was quite a programming achievement for me, because it had to take into account hardware scrolling, mode changes, and logical colour palette definitions!

In December 2009, I was able to record my Acorn Atoms using a composite video lead which came with the first of my Atoms. Unfortunately, the picture was extremely unstable on the DVD recorder, constantly rolling vertically around the screen. I had first tried this in September 2009 but had given up after being unable to stabilise the picture. I tried again in December 2009, thinking I might be able to record sufficient material to extract frames at the moment the picture lined up into the correct position. The result was a little bit hit-and-miss but generally it worked. To prevent myself going dizzy whilst doing all this, I also had the Atom connected up to a TV set via the RF output so I could at least see what I was doing!

In summer 2010, I replaced my cheapo DVD recorder with a much better JVC one. The new one understands RGB, which means I can now record onto DVD using a BBC RGB-to-SCART lead. This has allowed me to make even better quality Beeb screenshots than I could achieve with the composite video output. It has also meant for the first time I could record the screen output of some of my later 32-bit Acorns which don't have a composite socket, such as my A5000 and A7000.

The biggest benefit of all has been that I can now record proper screenshots of the Domesday System, which was not possible previously as the BBC micro RGB overlay always got lost in the recording.

The method of making the DVD recording into a picture set is much the same as with my first DVD recorder, but the frame size on the JVC one is 720x576. Also the ffmpeg command has been superseded by avconv which requires very slightly different parameters but is basically the same. Since January 2016, I've not reduced the JPEG quality when suffixing the images in Phatch. File size isn't so much of a priority now, and producing screen images with minimal JPEG compression artefacts is more important, although it will be a few years before these new, higher quality images filter through!

FFmpeg seems to have made a reappearance in Ubuntu, so I'm now back to that, and I'm using Converseen instead of Phatch with effect from Ubuntu 18.04.

Unfortunately, the JVC DVD recorder has been on the blink over the last couple of years. It seems to eat DVDs now, occasionally breaking down in the middle of a recording, rendering the disc unreadable and losing everything recorded so far. I am on the lookout for a new DVD recorder, or even HDD recorder, but it looks to be getting difficult to get hold of kit which can accept SCART input.

In February 2011, I was given the suggestion that I might be able to record a more stable Atom picture using a PC TV tuner card. In fact, my PC has a TV card because I made it part of the specification when the machine was built for me in August 2003. I think I had the idea at the time that I might be able to use it to view pages from Teletext at a time before I had much experience of using Acorn Teletext Adapters.

The Tuner card has a composite input, so I could use the Atom composite video socket. It took a bit of doing and I had to use an unusual video setting - PAL 60 - to get the picture, but once this was tweaked, I could use VLC to display a live Atom picture and take screenshots whenever required.

You can see more about my two DVD recorders by clicking on the picture links above.




Updated 1st January 2019