Progressive vs Interlaced And Why Your Video May Appear Distorted
February 12th, 2012
When it comes to LCD screens, video cameras and DSLRs, everyone would have come across the most common terms for video modes like 1080p, 1080i, 720p, 720i, etc… but many people don’t actually know what the ‘p’ and the ‘i’ stand for.
They stand for pregressive and interlaced respectively.
Another important thing that, as a film maker, you should know is pixel aspect ratio. Sometimes when you export your video, it may appear stretched or squashed because your pixel aspect ratio is incorrect.
Hopefully this week’s video will be able to clarify these things
Progressive vs Interlaced Video Mode
All film consists of a sequence of images that is (usually) played back at at least 24 frames per second. In digital video, each frame is a grid of pixels and with each new frame, the pixels on your display are updated with new colour values. However, depending on what video mode you are using, not all pixels may be updated with each new frame.
This is where progressive and interlaced video differ.
In progressive video, all pixels on your screen are updated with each new frame. This ensures smooth animation, but requires more data to be stored (and thus bigger file sizes) for each frame of video.
In interlaced video, each frame only updated every other row of pixels, alternating between the odd and the even rows. This means that it takes 2 frames for all pixels on your screen to be updated and, because less data needs to be saved for every frame, leads to smaller file sizes.
However, it does lead to very ugly video artefacts, especially around the border of moving objects
If an object is moving through the frame very fast, it will be at very different positions in consecutive frames. However, because interlaced video only stores every other row of pixels, when played back, strong horizontal lines can be seen where the object has moved.
I highly recommend to avoid interlaced video wherever possible. It is not always easy to de-interlace your video and it will save you a lot of headache to ensure your camera/display supports progressive video
Pixel Aspect Ratio
On your computer screen, all pixels are square. However, when it comes to video cameras, film and broadcasting standards, not all pixels are created equal. Sometimes pixels are more wide than they are tall. The relationship between the width and the height of the pixel is referred to as the pixel aspect ratio
Why should you care about pixel aspect ratio?
If you are a film maker or have recorded some video with a DSLR camera or a camcorder you may have encountered the problem of you video appearing stretched or squashed when you load it into your post production software or display it on a tv screen.
The most common reason for video to appear stretched or squashed is that the pixel aspect ratio used during displaying the video does not match the pixel aspect ratio that was used to record the video.
Assume you have a video recorded with a pixel aspect ratio of 1.333 (many camcorders record at 1440×1080 with a pixel aspect ratio of 1.333).
Your video comes out of the camera like this:
Now if you display this video on a display or in your post production software using a square pixel aspect ratio (1), then the video will appear squashed:
Conversely, if you recorded a video at a square pixel aspect ratio, your video would come out of your camera like this:
If you displayed this video using a pixel aspect ratio of 1.333, the footage would actually appear stretched.
If your video appears stretched or squashed, check that your pixel aspect ratio setting matches the pixel aspect ratio of the camera you used to record your footage
It is almost Valentine’s Day and, well, what is more romantic than a bunch of trash bins proclaiming their eternal love for the garbage man in a song?
Happy Valentine’s Day!
There were two parts to creating this Valentine’s Day music video:
Composing the barber shop style love song
Filming and syncing the trash bin lids to the voices
Composing the Valentine’s Day love song
I have never tried to compose an a-capella piece, but once I had the melody line and the chords down it was actually not too difficult
I ended up having the bass and the baritone (leftmost 2 trash bins) sing over the base notes from the chords while only the tenor carried the melody notes.
To add a bit of variation and make it sound a little more interesting, the bass and baritone only follow the main vocals half the verse and then break out into longer, more background style vocals. This also helps make the chorus line stand out cleanly against them
During the chorus I added a choir group containing a bass, a tenor and one soprano voice (sung I head voice).
I have to admit that I ended up using a fair bit of auto tune as I’m not a terribly great singer and the tenor voice of Willis is pitch shifted up by 4 semitones because I could not sing high enough But I am pretty happy with the results and the feel of this Valentine’s Day song.
Shooting and syncing the trash bins
Once I had the music for the Valentine’s Day song, I had to combine it with the footage.
I attached a fishing line to each of the bins separately and filmed the lid moving up and down once. In post production I had to edit out some of the parts whe the fishing line, because it was sometimes clearly visible in the direct sunlight.
The stage of synchronizing the lid movements with the audio is probably where I spent the most time.
I placed the footage in After Effects, duplicated the trash bins with the cloning effect and enabled time remapping on them. With the music added, I then matched up the opening of the lids with the volume of the individual voices. For this, I used a little trick.
I used Motion Sketch to record my mouse movement on a Null object and linked the time positon of the trash bin to the x coordinate of the Null. When the Null was on the left side of the screen, the lid would be closed, if it was on the right side of the screen, the lid would be fully opened. I then played back the track and, with my mouse, recorded the lid movement to match up with the audio.
I repeated this for all trash bins
Finally, I added some colorisation and a little bit of story around the Valentine’s Day love song to wrap it all a little better
Common green screen mistakes and how to avoid them
January 18th, 2012
I love using my green screen for visual effects. If used properly, it allows for a vast number of cool effects to be created with relative ease However, if you are not careful during filming you could end up with a number of problems in post production that will hinder if not completely block the visual effect you had in mind.
To not let all my failed attempts go to waste, I decided to create a video tutorial on the most common green mistakes and how you can avoid them!
1. Shadows on the Green Screen
Position your subject a little bit at a distance to the green screen to reduce the shadows.
Try to avoid a single hard light on your subject which will cause strong shadows.
Add lights aimed at the green screen to brighten up the dark areas.
2. Unevenly lit Green Screen
Move or add lights to ensure the most even lighting you can get for your green screen.
3. Motion blur in front of Green Screen
Try to have your subject move slowly to avoid motion blur to begin with
If you need fast movement, use a higher shutter speed (a smaller shutter angle) to avoid motion blur. Because this will cause your footage to look a certain way, you can add blur back in post production – AFTER you applied the green screen
4. Clipping out of the Green Screen
Doesn’t happen to you, right?
It’s easier than you think and because it’s usually just by a little bit, everyone thinks “eh, no big deal”! But it’ll really annoy you in post production. I recommend reshooting the footage!
5. No backlight
Add a light between the green screen and your subject but aim it towards the camera at the back of your subject. This will create a nice highlight outline around your subject and give it shape and make it stand out nicely against the background
I hope these tips will be helpful when you’re doing your next green screen shoot! I certainly learnt them the hard way hehe
I love creating short films and visual effects, but admittedly it always takes me forever to get the next project completed. Since I somehow enjoy teaching people new things, I have decided to start creating visual effect tutorial videos on my SurfacedStudio YouTube channel as well
I don’t consider myself an expert and I often learn tons of new things myself when I’m creating these tutorials, but today I have a very simple visual effect tutorial for all of you: how to create a clone!
Visual Effect 101 – How To Make A Clone
Tips & Tricks
It’s easy to create clones of yourself as long as you do not overlap or interact with yourself, but what if you want to? What if you want to hand a package from one clone to the next or have an army of them come up and gather around a table where there is not enough space for all of them to stand side by side? In this case, you have to be a bit smarter about your visual effect!
Overlapping with yourself
Green screening will allow you to (fairly) easily overlap yourself with your clones without having to manually rotoscope them. By using a green screen you end up with footage of your clone on a transparent background and it will be easy to place them in the scene. Incidentally, my next YouTube tutorial will be on green screening hehe
Interacting with yourself
This is a tricky one and you will most likely need another person for this. Let’s say you want to hand a package from one clone to the other. As clone 1, act out the scene until the moment you pass on the package. Have someone else take the package from you and pretend to be your clone. Then, have that person pretend to be clone 1 while you act out the part of clone 2, who is receiving the package.
The difficult part will be to ensure the package is in the same position/angle when you hand it over to your clone so you can cut together the footage without any obvious cuts. It is tricky but can be done, I have often seen CG employed as well to ‘smooth’ over the moment of interaction.
Either way, I hope you have fun with the cloning visual effect! There is a lot of great things you can do with it and you sometimes never know whether something will work until you try it!
Ever since filming The Doppelgänger together with Fables In Fashion, I’ve had an idea to create another action video that ties in with the story line and provides a little bit more of a conclusion
I must have spent about 3 weeks purely doing post production on this short film as virtually every scene contains some sort of visual effect. It was a bit daunting, but also great fun and a great learning experience to delve into compositing 3d rendered elements with real footage and I can’t wait to do more elaborate visual effects in future video projects.
I am quite happy with the results and hope you will enjoy this short film
At War With Your TV – VFX Short Film
I am always happy to receive any feedback for my video projects, so feel free to leave some in the comments below. If I get around to it, I might go over a few of the visual effects and talk about how they were created in some tutorial videos
