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
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!
Here is a quick summary of the 5 most common green screen mistakes and some tips on how to avoid or fix them
1. Shadows on the Green Screen
The Problem
If your subject is too close to the green screen or the light from the front is too strong, a dark shadow might be cast onto your green screen.
This can cause unpleasant artefacts when you finally try to apply the chroma key. Because the dark areas on the green screen are too close in colour to the dark areas of your subject it may be hard to key them out cleanly.
On the right side it’s hard to tell where the arm ends and the shadow on the green scren begins.
The Solution
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 behind your subject that are aimed at the green screen to brighten up the dark areas.
2. Unevenly lit Green Screen
The Problem
This problem is very similar to the previous one. While the green screen is now better lit, the lighting is very uneven, creating dark and bright areas in the background.
Again, this can make the application of the chroma key difficult without clipping away parts of your subject. Here is an image of what the unmodified screen matte looks like.
The Solution
Sometimes you can rectify the solution in post by carefully controlling the ‘deposit black’ and ‘deposit white’ parameters in your Keylight Effect (if in After Effects). Other compositing software chroma key effects will have similar options, so try this first
To prevent getting into this situation to begin wtih, try to add lights aimed at your green screen to even out the lighting before you shoot.
3. Motion blur in front of Green Screen
The Problem
If you shoot at a slow shutter angle, you may end up with motion blur in front of the green screen.
This is something that is really hard to fix in post production since the areas where the motion blur occurred will be blended together with the green screen. It can be hard or even impossible to set up a clean chroma key without losing parts of your subject.
The Solution
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 impose a certain hypersensitive onto your footage, you can add the motion blur back in post production – AFTER you applied the green screen
4. Clipping out of the Green Screen
The Problem
You shot in front of your green screen and the subject was out of the screen for just a short moment. Not a problem, right? Fix it in post?
This can be very annoying to fix as you will have to manually rotoscope out all the elements that left the green screen.
The Solution
While the rotobrush tool in After Effects may help make the job easier, I strongly recommend reshooting the footage if you can
5. No backlight
The Problem
This is not really a problem, more a tip on how to make your subject stand out a little cleaner against the green screen. This will make application of the chroma key a lot easier and it will help give the actor or object a bit more shape by lighting them smartly
If you just shoot your subject against a green screen with light from the front, the outline of the subject is not very well defined.
The Solution
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 am getting more and more addicted to creating more elaborate visual effects
One thing I have always wanted to do since watching Freddie W’s Fire Hands video is to make my own video of me creating fire with my hands.
Now I didn’t just want to copy their idea and to be honest, I almost get the feeling the fire in Freddie’s video is real rather than a VFX, and so I came up with my own little video idea.
What do you do when the lights go out but you have no matches to light your candle? Use your hands!
VFX – Making Fire With Your Hands
I am planning on putting up a small video tutorial for this fire effect as well
Or at least cover how to make proper fire/candle/gun lighting effects and composite them more onto your footage – I seem to find too many videos where the ‘lighting’ is just a mask stuck over the footage using additive lighting.
Man vs Wild parody filmed in the Dandenong Ranges, Australia
November 16th, 2011
I have always been a big fan of Man vs Wild with Bear Grylls.
People may argue about how much of the show is ‘real’ and get all upset that OMG he dared to have an actual safety rope while crossing a 200m deep gorge on an old power line. But honestly, I don’t care
Bear Grylls is such an inspiring and positive character, it’s hard not to like him and feel motivated when watching him climb, swim, crawl and eat his way through some of the toughest terrain on this planet.
For me, I have always loved adventure but had gotten a bit stuck in work and everyday routine. It was watching Man vs Wild that reignited my desire to be out in the wilderness, go climbing and exploring and enjoy the beauty this world has to offer
In honour of Bear Grylls, I always wanted to make a Man vs Wild spoof video – not with mocking, evil intent, but instead as a hommage to his undefeatable spirit and his endless enthusiasm for the wild
A few weeks ago, I went on a hike with my friend Alex and decided it was time to shoot the footage needed to make my Man vs Not So Wild video!
I hope you will enjoy it
Man vs Not So Wild – Man vs Wild Parody
The video was shot up in the Dandenong Ranges just east of Melbourne, Australia.
We shot most of the footage just off the main hiking tracks with the camera aimed into the rainforest to give a feeling of actually being surrounded by it. Before I got to sound editing, I wasn’t too sure the illusion would work as there were plenty of moments when you could hear cars, people talking and even a helicopter flying by
Lots of things went wrong during the shooting and just for the fun of it I made a small outtakes video. If you want to see a bit behind the scenes footage and have a bit of a laugh at the stupid stuff we did (or tried to do) during the shooting of the actual video, here is the outtakes reel:
After a lot of awkward talking into a camera, I finally managed to finish my video tutorial on shutter angle! If you are not sure what shutter angle is and how it can help you make your DSLR video look more like film, please watch my latest SurfacedStudio tutorial
Shutter Angle Tutorial Video
In addition to the video I have written up the following tutorial to go into a few more details on shutter angle and why it is so important.
Common mistakes when shooting video with your DSLR
Have you ever taken a video with your DSLR and it ended up looking more like some cheap home made clip rather than high quality film? While there are a lot of steps taken in post-processing to make the footage look sleek and polished, one simple principle you can utilise right now to improve the quality of your videos is shutter angle.
When you take video with your DSLR in automatic mode two bad things will happen:
The brightness will constantly change as the camera tries to keep your film at ‘default’ brightness. This causes the video to look very ‘home made’
The brightness is adjusted by constantly changing the shutter speed of your camera. This behaviour is called a ‘rolling shutter’
To understand why a rolling shutter is a bad thing we need to discuss the effect shutter speed has on your video.
The effect of shutter speed on your video
The shutter speed of your camera controls how much motion blur you will see in every single frame of video footage. Unless the amount of motion blur in the video is similar to the amount we see in our every day lives, the footage will not feel natural to us. Our brain will perceive the differences and distance us from what is happening on screen
Have a look at these two images:
The falling ball in the left image has a lot more motion blur because the photo was taken with a slower shutter speed of 1/30s. The falling ball on the right side has a lot less motion blur because the shutter speed was faster at 1/100s. While this example is a photo, the effect of shutter speed on video is the same! The amount of motion blur in every single frame is controlled by your shutter speed.
A rolling shutter is bad for video because the constant change in shutter speed changes the amount of motion blur from frame to frame, creating a very inconsistent feel
Most of the time, we are used to seeing a certain amount of motion blur with our naked eye – just try to swipe your hand in front of your face and you see what I mean. Sometimes we have ‘blurry vision’ and all movement around us seems to leave more streaks than normally. Other times we receive an adrenaline rush and suddenly everything we see and hear appears were sharp and rich in details.
By using a specific (fixed) shutter speed we can give our film a certain amount of motion blur, depending on what effect we are after:
By using a slow shutter speed, every frame of video will have more motion blur than we naturally see and thus the footage will appear blurry and smooth
By using a ‘normal’ shutter speed (I will discuss this below), every frame of video will have an amount of motion blur that approximates what we see every day with our eyes. This shutter speed is most frequently used in most motion pictures
By using a fast shutter speed, every frame of video will have very little motion blur and the footage will look as if we were experiencing an adrenaline rush
Why is it called Shutter Angle?
In analog motion picture cameras the shutter is a spinning disc called a rotary disc shutter. The film is being pulled through the camera one frame at a time and the shutter rotates in front of the film to control how long each frame is exposed.
This shutter rotates at the same speed as the framerate. For 24fps, the shutter rotates 24 times a second. For 30fps, the shutter rotates 30 times a second. The shutter disc has a certain angle cut out of it and every time the cut out moves over the frame, light can reach the frame and expose it. How long each frame is exposed is determined by the angle of this cut out.
And it is this angle that is referred to as the shutter angle
At 24fps, the shutter rotates 24 times a second, each rotation taking 1/24s.
At 180° shutter angle, the shutter is basically cut in half and each frame is exposed for half the time it takes the shutter disc to do one full rotation. One full rotation takes 1/24s, so each frame is exposed for exactly half of that time, which is 1/48s.
At 30fps, the shutter rotates 30times a second, each rotation taking 1/30s.
At 180° shutter angle, each frame is exposed for half the time it takes the shutter disc to do one full rotation. One full rotation takes 1/30s, so each frame is exposed for exactly half of that time, which is 1/60s.
It is important to notice that the shutter angle describes the shutter speed in relation to the framerate. When you keep the same shutter angle but you change the frame rate, you need to adjust your shutter speed accordingly
Why 180° makes your video look like film
Typically, motion pictures are filmed at a 180° shutter angle. Lately, 90° is used a fair bit in war or horror movies to make the footage more intense and give the viewer an adrenaline rush feeling, bust most of the films you will see in the cinema use 180° because it has the motion blur that most closely approximates the motion blur we see with the naked eye.
So if you want your DSLR video to look more like film do two things:
Set your camera to manual mode during recording. You might have to manually adjust the ISO setting or the aperture to make sure your image has the correct brightness. Yes this is more work, but believe me, it’s worth it
Set your shutter angle to 180°: if you’re shooting at 24fps, use 1/50s shutter speed (1/48s would be more exact, but most cameras don’t have that option so 1/50s will do ). If you are shooting at 30fps use 1/60s.
Finally, here is a table summarising the framerate, shutter angle and effect most commonly used in motion pictures
FPS
Shutter Angle
Shutter Speed
Effect
24 fps
240°
1/36s
Every frame has a lot of motion blur resulting in slightly streaked, very smooth footage. Almost ‘drunk’ effect
30 fps
240°
1/45s
24 fps
180°
1/48s
‘Natural’ amount of motion blur. Most often used in motion pictures so use this setting to make your DSLR footage look like film
30 fps
180°
1/60s
24 fps
90°
1/96s
Very little to no motion blur resulting in a very ‘intense’ feel of your footage. Often used in war or horror movies to emphasize details
30 fps
90°
1/120s
I hope this tutorial was helpful to you and if you have any questions, please let me know and I will try my best to answer them and update this tutorial
The unification to SurfacedStudio is finally complete
October 15th, 2011
Welcome to SurfacedStudio!
I am very excited to have completed the migration from surfacedmusic to SurfacedStudio
The reason for the migration was mainly to get away from the ‘music’ part of my website. Not that I am going to stop writing music, far from it. I just love so many different creative activities and wanted to have one location where I could keep and share all of them.
Recently I have gotten more and more interested in video production and special effects. I have always been an avid photographer and as a software developer by profession I love developing video games and random small tools to make my life easier. I still love to write, compose, record and mix music, but I also want to have a place to talk about and share anything else that interests me – that place is going to be SurfacedStudio
Here is my latest video project that I did with Fables In Fashion. It’s a dark action video clip in Underworld style. I composed the music for it and added the special effects
New music videos are finally being uploaded onto YouTube
June 19th, 2011
I have finally managed to get my (properly styled) YouTube channel online and have started uploading the first videos
I already have a few musical drafts online that I want to eventually develop into full songs. Since I have only recently gotten my hands on a shiny new Nikon D7000 (which can also take awesome full HD movies), the current videos are sporting a simple image and text only.
The plan is to keep uploading smaller fragments regularly while working on full length songs. For the full length songs I want to create actual music videos as well – how long this process will take I am not sure yet, we shall see.
I am currently working on a song called ‘Rise Up’ which will be my first attempt at a full music + video project
There are lots of other ideas floating through my head now on what I want to put onto YouTube
I have already picked one of those ideas and want to properly film, cut and polish it – and of course I will be making the music for it too! Hopefully I will get to film all the material I need this coming weekend!
Besides getting more into video recording (and special effects – thank you After Effects!), I have mainly been working on a proper recording plan.
I have been pretty badly stuck with my music lately, ending up with hundreds of fragments and no complete songs. Trying to bust through that block, I have laid out a strict plan to follow for the next few months.
My plan schedules the release of 5 currently unfinished songs, properly composed, recorded, mixed and mastered by October. I might end up making a small video diary for the process – hopefully recording some useful information on how to get out of a rut along the way
For now, here are a few of the song drafts I have already online.
For more videos, please visit my YouTube channel.
Any feedback or suggestions are always welcome
