I recently reviewed the rather excellent Sonnet QIO I/O device that allows you to very quickly ingest material from SxS cards, P2 cards as well as SD cards to your computer. Along with the QIO I was sent a Sonnet SDHC to SxS card adapter to take a look at. Now I’m going to lay my cards on the table here and say that I strongly believe that if your going to shoot with an XDCAM EX camera you should be using SxS cards in order to get the best possible reliability. However as we all know SxS cards are expensive, although a lot cheaper now than they used to be, I remember paying £600 for an 8Gb card only 4 years ago!
So ever since the launch of the XDCAM EX cameras, users including me have been trying to find alternative recording solutions. I found that it was possible to use an off-the-shelf SD card to express card adapter (the original Kensington Adapter) to record standard frame rates on class 6 SD cards in the EX cameras. However the SDHC cards stick out of the end of the generic adapters so you can’t close the doors that cover the card slots in the cameras. Following that initial discovery various companies have brought out flush fitting adapters that allow the use of SDHC cards. Then about two years ago Sony openly admitted it was possible to use an adapter in the cameras and released their own adapters (MEAD-SD01 and MEAD-MS01) as well as making some firmware changes that made using adapters more reliable. The key point to consider when using an SxS adapter and SD cards is that the media, the SD cards, are consumer media. They are produced in vast quantities and the quality can be quite variable. They are not made to the same standards as SxS cards. So I choose to shoot on SxS whenever possible and I’ve never had a single failure or unexplained footage loss. BUT I do carry a couple of adapters and some SD cards in my camera kit for emergencies. You never know when you might run out of media or find yourself in a situation where you have to hand over you media to a third party at the end of a shoot. SDHC cards are cheap and readily available. You can buy an SDHC card just about anywhere. I’d rather switch to SDHC cards than try to do a panic off-load to a backup device mid-shoot, that’s a recipe for disaster!
Anyway… on to the Sonnet SDHC to SxS adapter. It feels as well built as any other adapter on the market. It is mostly metal with plastic end pieces that are made from a nice high quality plastic. I have other adapters that use a very brittle plastic and these can break quite easily, but this one appears to be well made. The SDHC card slots into a sprung loaded slot in the end of the adapter making a reassuringly positive sounding click when it’s latched in place. Once inserted the SDHC card is slightly recessed into the adapter. This is good as it helps prevent the SDHC card from being released from the adapter as you put the adapter into the camera. It means that as you push the adapter into the camera you are pushing on the end of the adapter and not on the SDHC card like some other adapters I have used. To remove the SDHC card you simply push it quite firmly, further into the adapter until you hear another click and it then pops out far enough to be pulled out. This is certainly one of the better made adapters that I have come across.
To test the adapter I used some Transcend class 6 SDHC cards as well as some Integral Ultima Pro class 10 SDHC cards. I used the adapter in my PMW-F3 with firmware version 1.10 as some user have reported problems with other adapters and this firmware revision. I was able to completely fill the cards shooting using S&Q motion at 50fps or 60fps using long and short clips with lots of motion. This is I believe the toughest test for these adapters as the recording bit rate is close to 70Mb/s. I had no issues at all with either type of SDHC card and there was very little delay between finishing a recording and being able to start the next, a good indicator of the cards high performance. I also tested recording very long clips to ensure that there would be no issues when the camera breaks the recording into 4Gb chunks. Again, no problem.
So if you are going to use SDHC cards and an SxS adapter I would suggest you consider the Sonnet SxS adapter. It’s certainly cheaper than the Sony adapter. Sonnet are a large business with a wide range of products and a global distributor and dealer network, so you should have no problem finding a local supplier.
This a recurring question that I get asked about time and time again. The main problem being that the SD pictures, shot with an HD camera look soft. So why is this and what can be done about it?
Well there are several issues to look at. First there is camera optimisation. Sadly what works for HD doesn’t always work well for SD. Secondly there is the downconversion process. If your shooting HD and simply outputting SD using the cameras built in downconverter than you really don’t have many options but if your using a software downconverter you may be able to improve the results your getting.
Starting with the camera, what can you do? Well first off let me say that a camera optimised for HD will always be a compromise when it comes to SD. As the native resolution of HD cameras increases then the problem of getting good looking SD actually gets worse. The problem is that a good high resolution camera will normally only have a very small amount of artificial sharpening via the detail or aperture circuits, because in HD it will look nice and sharp anyway. SD cameras and the SD TV system with it’s inherently low resolution and soft pictures has always relied very heavily on detail enhancement to try and make the pictures appear sharper than they really are. When you take the minimal additional sharpening of an HD camera and downconvert it to SD it all but disappears, the end result is a soft looking picture. There is no easy fix for this, you can either add additional extra thick detail correction edges to the HD pictures, which risks spoiling the HD image or you can add additional detail correction in post production. On a Sony camera the thickness of the detail correction edges is controlled using the “frequency” setting. Setting this to a negative number will thicken up the detail edges, very often you need to go all the way to -99 to get an appreciable difference. As an alternative you can add extra sharpening or detail correction in post, after the downconversion process. This is the way I would go whenever possible as I don’t want to compromise my HD pictures for the sake of the SD images.
The second issue is the quality of the downconversion. A simple rescale from HD to SD rarely works well as it can create a lot of aliasing. Aliasing is the result of taking too much detail and trying to record or represent it with too few pixels. See this article for more on aliasing. Imagine a diagonal line running through your image.
If you sample it at a high resolution, with your HD camera then the line looks reasonably good as you can see in the diagram to the left.
If you then take that HD captured edge and simply scale it down to SD, you quarter the number of samples and the end result is a jagged, stepped line. Not pretty. In addition, if the line moves through the image it will flicker and “buzz”. This is far from ideal.
A better approach is to blur the HD image before down converting using a 4 pixel (or similar) blur, or to use a downconversion programme that will include smoothing during the conversion. The final image shows the kind of improvement that can be gained by softening the image before down conversion. The blur around the edges of the line soften it and make it appear less jagged. This will result in a much more pleasing SD image. Next you then add in some detail correction to restore the apparent sharpness of the image and viola! A decent looking SD image from an HD source. In compressor to get a good downconversion you need to activate the advanced scale tools and use the “better” or “best” scaling options.
Ever since the release of the XDCAM EX cameras users have been having problems getting good looking SD pictures out of downconverted HD.?Why is this and what can be done about it? This is an issue that effects all high resolution HD cameras and is not unique to the EX’s. There are two key issues. The first is the way basic software converters handle fields in interlace material and the second is the amount of information in an HD image that must in effect be discarded to get a SD image.?At first glance you would think that starting off with lots of picture detail would be a good thing, but in this case it’s not. Let’s see if I can explain.?Imagine that you have something in you HD picture that over 4 pixels goes from light to dark, in Hd you get a gradual transition from light to dark and all looks good. Now what happens when you take those 4 pixels and convert them to SD. The 4 pixels become just 2 and instead of a stepped change from light to dark the picture now goes instantly from a light pixel to a dark pixel. If these pixels were the edge of a moving object, as it moved the pixels would be switching instantly from on to off and unless the object moved at exactly one pixel per frame you will get a flickering effect. Clearly our nice gradual transition from light to dark has been lost and if there is any motion we may now be seeing flickering edges. Niether of these look good.
Take a look at these images:
As you can see the down converted SD is very blocky and there is some strange patterning (aliasing) going on amongst the bricks of the houses in the background. This does not look good and if there was motion the brickwork would shimmer and flicker.
So what can be done?
Well the best way to improve the SD down conversion is to soften the HD image before it is down converted to prevent this single pixel light to dark switch from happening. You need to end up with an SD image where you go from full light to full dark over at least 3 pixels to prevent flicker (Twitter).
How much you will need to soften you HD by will depend on how sharp it is to start with. Simply turning down the cameras detail settings can be a big help, but even then the best results are often obtained by applying some kind of blur filter in post production. In FCP I find the flicker filter works quite well. As you can see from the frame grab below the difference in the quality of the downconvert is quite striking.
I have also found that another problem is that the detail settings on an HD camera are not optimised for SD. The detail correction edges created in HD are very thin and when these are down converted to SD they all but disappear and can cause further aliasing. The solution is to make the detail correction edges thicker (on an EX turn detail frequency down to -60 to -99) but this then looks ugly in HD. The bottom line is that a camera optimised for HD works best in HD and SD will be a compromise.
Camera setup, reviews, tutorials and information for pro camcorder users from Alister Chapman.