In a previous post, I briefly discussed some of the specific concerns of working with footage from the Canon HV20. In this post, I will talk about these things in a little more depth, and with some example pictures to more fully demonstrate what I’m talking about.

Here is a full resolution frame-capture of a video stream shot with the HV20 (the image is a link to the full resolution image). All of the images posted here are compressed with jpeg 80% quality, and should have most of their original attributes preserved. Note that the pulldown has been removed with After Effects, and that this was originally a frame comprised of two interlaced fields. Note that this picture is HUGE (1920×1080), so if you have a regular sized monitor, expect to scroll around to look at it completely.

If you look closely at the image, you can discern fragments of interlacing artifacts left behind from the pulldown removal. This happens because the mpeg2 compression of the interlaced image results in fields that are imperfect with macroblocks and other imperfections. This confuses After Effects’ algorithms, leaving behind chunks of image that still have interlaced areas. Effectively this just looks like bits of the image have weird blocks of ‘liney’ areas. Below is a 4:1 crop of the above original frame, doubled in size.

You can notice these artifacts on the edge of the finger. In After Effects, there are plugins to process a frame to remove interlacing artifacts. With one of those applied, the image looks a little cleaner.

There are still noticeable artifacts from the mpeg2 compression. You can make out macroblocking and chroma abnormalities on the thumb and surrounding areas. If you were to look at the individual color channels, this would be more noticeable. Usually the compression artifacts are worse in the blue channel. There is a plugin that comes with the Magic Bullet Suite called the “Deartifactor” that takes a whack at removing compression artifacts such at as these.

Deartifacted:

Non-Deartifacted – Blue Channel Only:

Deartifacted – Blue Channel Only:

Sometimes it is hard to see what the deartifactor is doing in areas of detail. Here is another comparison in another less detailed area of the image.

Non-Deartifacted – Blue Channel Only:

Deartifacted – Blue Channel Only:

There is also a filter in After Effects called Remove Grain that was once sold as Grain Surgery by Visual Infinity, but is now included for free with After Effects. This plugin is quite amazingly good at removing grain while preserving detail in the image. While the compression artifacting is not quite grain, it does do a fair amount to improve the apparent image clarity, and while it does soften the image some, it can be adjusted for good results.

Remove Grain filter applied:

Here is the final processed image, in full resolution.

Most likely the effective qualitative differences in the image when viewed full-resolution are relatively minor. However, when you get into things like doing dramatic color correction or other processing, or attempting to extract a matte from an image using color keying, it is absolutely essential to have the best quality image that you can to work with. Of course it is not really a great idea to try to use HDV for something requiring excellent chroma key matte extraction, but for 800 dollars, this camera produces some amazing images, and you would be hard pressed to find a better solution for less than several thousand. There is also the possibility of capturing 4:2:2 uncompressed video before the MPEG2 compression stage from the HDMI output of this camera, if you have a Black Magic Intensity card, or an equivalent HDMI capture device, which could theoretically be plugged into a laptop. There has been some experimentation in this area, but little noticeable benefit is likely to be achieved.

As free alternatives for the post-processing of HDV, there is a plethora of possibility with AviSynth and various other freeware windows applications. There is quite a bit of activity around the area of using AviSynth for post-processing of HV20 footage.
The Farnsworth plus Sillyman Process
Automated 24p pulldown workflow using DGIndex and VirtualDubMod
Morgan MJPEG2000 as an alternative HD Intermediate Codec
AVISynth and VDub Templates / Code

To end this post, here are some other full-frame image-captures from the HV20, with no processing applied to them other than pulldown removal and deinterlacing.

An indoor image recorded in low light, showing the characteristic of the camera in high-gain mode, which can be avoided if operated properly.

An outdoor image from the camera on a relatively bright day.

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Among the constant plethora of activities in the area of technical matters, (that I sometimes seem to use as a form of procrastination from ‘real’ work), I have been doing some interesting things.

I have been going through the manual and tutorials on Nuke, and am quite struck by its differences from After Effects. Nuke is less friendly in the construction of the user interface, and yet very powerful. Like many compositing applications, it features a node-based interface. A node-based interface is basically a different way of combining different elements into a final image. An image or moving image is loaded in, and then multiple nodes are linked together in a stream, each applying some process to the image. This combination of nodes forms a ’script’, which is much the same as a project in After Effects. After Effects features a layer-based interface, where different elements are stacked on top of each other in layers, and the layers are arranged in time. This is what I am used to, but a node-based interface is beginning to make sense for some more complex projects using many image elements.

I have also been working through some more advanced tutorials on texturing and modeling in Maya, attempting to build on what I learned this summer, and gain the knowledge I will need to actually create some of the crazy things I have in mind for this project.

Close to the end of Week 06, I received a new HD video camera, the Canon HV20. Purchased from Newegg.com for $799, it is capable of shooting 1080p24 in the HDV format. I will be using this to acquire textures and live action image elements for my project at a high enough resolution to successfully work at 1080p24 for the final output. Of course with a new acquisition format, there is a great deal of testing and learning to do in order to become comfortable with a post-production workflow.

Because the HV20 is capable of recording in 23.976 progressive frames per second, and the HDV format specification calls for interlaced 29.97 frames per second material, the HV20 has to do some processing to record its beautiful progressive data to an HDV tape. Similar to the Panasonic DVX100, which records 23.976 progressive fps standard definition material in a 29.97 interlaced fps video stream by applying a pulldown to the footage, the HV20 records a 1080p24 stream of video, but packaged in a 1080i30 video stream in order to conform to the HDV standard. The fact that editing system support for the HV20’s footage is somewhat spotty that a process of removing the pulldown outputting to an intermediate codec is a necessary step. Adding additional complication is the image quality of the HDV format itself. Since the format uses mpeg2 compression, there is a relatively significant amount of image artifacting compared to DV. A step that many experimenters with this camera have been using to improve this situation is to add an artifact-removal step to the process. This way, the original footage from the camera can be processed from it’s original mpeg2 format, having its pulldown removed to achieve progressive frames at 23.976 fps, having compression artifacts filtered to improve the image quality, and then outputting the footage to a relatively lossless intermediate codec for editing and post production work (such as mjpeg2000, apple intermediate, pro res 422, or uncompressed). Of course with the adoption of HD intermediate codecs, more difficulties arise with storage space because of the extremely large size of uncompressed HD video, playback issues because of the extremely large data throughput needed to play uncompressed HD video (and the relatively limited transfer rates of hard drives), and so forth. For a large documentary, it would likely make the most sense to edit the footage in the acquired format of HDV and trust your editing system to deal with mid-GOP cutting recompression issues in an intelligent fashion. For this type of project however, because it is more animation and effects oriented, it makes more sense to have uncompressed files to work with… or at least I think it does.

On the bright side, the images from this camera look simply amazing, and I am very excited to incorporate this technology into my project, and figure out what will be the least painful method of working with the footage. Of course my primary goal is to make a good work of media, not to get caught up in the technology to the exclusion of all else, but I don’t think I am falling off of that cliff quite entirely yet.

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