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Getting good SD from an HD camera.
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.
Ultimate Documentary Production workshop. (3D as well if enough interest)
I’m planning on running a Documentary production workshop and 3D workshop based on a Storm Chasing trip to the USA from the 4th to the 12th of June. The trip would be an excellent chance to really put your documentary skills in to practice and learn more about your cameras and workflow shooting a short film about the violent weather that hits Tornado Alley every spring. We can even shoot in 3D if that’s what people are interested in. I can provide a PMW-F3, lens kit and EX1R, but hopefully you would bring your own cameras and I can teach you how to get the most out of them. depending on the weather each day there would be a classroom session or practical on location session covering everything from sound and interview techniques, to camera setup and shooting tips. Will will do a lot of timelapse, make use of cache record (if you have it) and work in some very challenging lighting situations. Each member of the group will be given different roles to play as part of the “crew” each day so that they may gain a better understanding of the difficulties of each role. At the same time the idea is that each person will also create their own personal short film about our storm chasing adventure. With luck we should see incredible thunderstorms, giant hail and maybe even a tornado or two (I’ve been storm chasing for 12 years, it’s my speciality). The cost for this comprehensive and very exciting workshop will be $1800 USD per person for a place on the course. In addition to that each student will be responsible for their overnight accommodation. Typically we will stay in hotels/motels that cost approx $100 USD per night, so you should budget for approx $800 for accommodation bringing the total to $2600. We will depart from Denver, Colorado so you will have make your own travel arrangements to/from Denver. This will be a real educational adventure. The previous trips I have run to Norway for the Northern lights, Arizona for lightning and Tornado Chasing have been great successes with many people returning for more. We will spend a lot of time on the road, visiting many parts of the Mid-West. It will be fun and you should come away with improved video skills, a great short film, and amazing stories of adventure and excitement. Please use the contact form if your interested. Places are limited.
Look how small the Gemini is!
Just obtained a picture of a pre-production Convergent Design Gemini mounted on a Panasonic AF101. It really shows just how compact this device is. The LCD is 800×400 resolution and a very bright 800 nits, which is nearly twice as bright as an iphone or ipad! You have to remember that this is not just a monitor but also a 4:4:4 10 bit, uncompressed recorder! With a street price of less than $6k this will be the perfect match for the Sony PMW-F3.
Lens Tests at F3 Dubai Workshop.
Off to the airport to fly home in a minute, but I thought I would jot down some notes about the various lenses we were able to look at during the F3 workshop I ran here in Dubai. We had a set of the Sony PL primes, a Zeiss CP2, some Zeiss ZF.2 stills lenses, a Nikon 50mm and a Tokina 28-70mm ATX pro zoom. The stills lenses were all attached to the F3 using an MTF to Nikon adapter.
It was hard to see any difference between the Sony primes and the CP2, this was kind of expected. When comapring the PL’s to the Tokina zoom, the zoom was a little soft wide open at f2.6. Stopped down half a stop and it looked much better, but it needed to go down to f4 before it came close to matching the PL’s. Even then the PL’s had the edge, but then this is comparing a zoom to a prime. I would certainly have no hesitation over using the Tokina at f4 or more closed. The Nikon 50mm pancake, f1.8 was surprisingly good. Even wide open it produced a respectable image, stopped down to f2.8 it was a very close match to the PL’s. The Zeiss ZF.2’s were the budget stars of the show as even wide open these produced sharp, clean images with very similar bokeh and flare performance to the primes, very impressive performance.
Of course ergonomically the PL’s were better. Bigger focus rings, bigger iris rings and better focus scales. The CP2 impressed with it’s near 360 degrees rotation of the focus ring with very clear and accurate witness marks and wide distance spacing even approaching infinity. If I could afford a set of CP2’s that’s what I would buy, but I can’t. The Sony PL’s are good lenses, they don’t quite have the build quality of the CP2’s but they do represent excellent value for the money. If your budget won’t stretch to PL glass then the Zeiss ZF.2’s are about as close as you’ll get to a PL lens, but do watch out for the amount of telescoping when you focus the longer focal length ones. That can make using a matte box very tricky. I know my Nikon 50mm and Tokina 28mm primes work well. The Tokina 28-70 while not as sharp as the primes will still make a good all-round lens. All I need now is to get a nice 85mm and 135mm and I’ll be happy. Maybe a couple of ZF’s.
Sony FS-100 Super 35mm NXCAM Camcorder Announced.
Well the rumours have been circulating for some time and prototypes have been seen at various trade shows, but the full details have been sparse to say the least. Well here it is, it’s called the FS-100 and it’s a quite radical design from the Sony Shinegawa factory. The Super 35mm NXCAM shares the same sensor as the new PMW-F3, so the images will be excellent, but the design of the camera body itself could not be more different. If you don’t like it… well you can blame me and several other DoP’s that were invited to attend brainstorming sessions with the Sony engineers. In the photo below you can see the white board from one of those sessions and you can see where we (me and the other DoP’s) discussed ideas like a modular design with removable handles and how we hold handycam cameras.
The end result is this rather quirky but in my opinion, really quite clever and versatile design. The top viewfinder allows you to use the camera cradled in your hands in front of you, either using just the LCD panel or the monocular viewfinder. When your doing interviews you can twist it so that it is visible from either side of the camera, excellent for those interviews where you are both camera operator and interviewer. It allows you to alternate the sight lines from left to right of the camera for more varied interviews. It’s also useful for shooting in cramped locations such as in the front of a car as you can hold the camera sideways in front of you to shoot… I mean film…. the driver and still see what your getting.
Unlike most traditional camcorders the camera can be stripped down to just the sensor/recorder body. You can remove the top handle, mic holder and hand grip. In addition it has a multitude of tripod mounting holes on the top, bottom and even one side. On the base of the camera there are 6x 1/4″ threaded holes and wait for it… 2x 3/8″ holes. Hooray!! On the top there are a further 3x 1/4″ holes and there is even one on the side, revealed when you detach the removable hand grip. This is going to be fantastic for use on cars as a 35mm minicam or crash-cam. It will make getting all those different car chase angles so easy as a few small suction mounts will allow you to mount the stripped down camera just about anywhere. I can see the FS-100 becoming a “must-have” B camera to compliment my F3. The 1/4″ thread on the side of the camera means you can mount it on it’s side for portrait style shooting for digital signage or to get the maximum resolution when shooting people for chroma key.
While the camera does come with a detachable handgrip, there is no zoom rocker like the F3. That’s because the camera is primarily aimed at those using DSLR lenses which don’t have servo zooms, although PL mount adapters are available. The front end of the camera has Sony’s E mount for interchangeable lenses. It will come with the rather nice (if a little slow) 18-200mm f3.5-f6.3 optically stabilised zoom lens and the auto focus and auto iris do work! As well as Sony’s own G series lenses for the NEX cameras you can get adapters for Sony A mount and most other lenses. Do consider that if you are planning on using heavy PL lenses that the E mount is not designed for such high loads, so an additional lens support system should be used.
On the input and output front the FS-100 has most of the connectors you would expect to find on an NXCAM camcorder, with one notable exception… HDSDi. There is no HDSDi, but don’t panic! The camera does have HDMI and the quality available from HDMI is every bit as good as HDSDi. No word as to whether it’s 8 bit or 10 bit though. Sony are well aware that the one thing missing from HDMI is normally timecode, but even that has been addressed and it will be possible to export timecode in the HDMI stream, although at the moment we need to wait for the HDMI recorders to update them to accept timecode via HDMI. There are 2 XLR connectors for audio in. One on the right side and one on the rear, there is also the usual mini-D component out and RCA/Phono audio and composite video outputs.
When you start to delve into the cameras frame rates and recording modes things get really interesting as the FS100 will record full 1920×1080 at 60P and 50P. Even the F3 can’t do this internally (you can output 50/60P to an external recorder). As well as all the usual frame rates like 23.98, 60/50i, 30/25P you can also shoot full resolution slo-mo at up to 60fps using S&Q motion. It’s not quite as flexible as the F3 as you will find that you only have a choice of frame rates (for example 1,2,3,6,12,25,50fps) and won’t have the ability to dial in any frame rate you want, but all frame rates will be full 1920×1080. As with the other NXCAM camcorders all these lovely modes will be recorded on to SD cards or Memory Sticks using the AVC HD codec (mpeg 4), in addition you can add the Sony FMU128 (128Gb Flash Memory Unit) for dual recording giving peace of mind with one off events.
Once your footage is on your cards the cleverness of this camera continues as you don’t need a laptop to backup your data. Simply plug in a USB drive or even a Blu-ray burner), direct to the cameras USB port and you can backup direct from the camera to the drive. Your footage will contain GPS data about when and where you shot it, which for me will be a great bonus with my severe weather footage as I can never remember exactly where I was during a storm chase!
All in all this is looking like one hell of a camcorder. The street price is estimated to be below $6000 USD, so you do have to ask the question.. why buy an F3 when this is half the price? In my view they are two quite different cameras for different applications. The F3 has the ability to output full 10 bit 4:4:4 for extremely high quality recording possibilities. It also has built in ND filters and will have S-Log and 3D dual camera control. For multi-camera shoots the F3 has Genlock and timecode in/out. There will also be some nice servo zooms for the F3 some time later this year or early next year. The F3 is a camera that would not at all be out of place as a B camera on a big budget production. The FS-100 will I’m sure also find a place on big budget productions, perhaps as a crash-cam or mini cam. But overall I think it will be most at home on more run and gun style shoots where auto iris and maybe even autofocus are beneficial. I really do think that the FS100 will replace many of the DSLR’s out there currently being used for video as a lot of thought has gone in to the ergonomics.
These are very interesting times. It’s now possible to shoot a movie, with quality good enough for mainstream theatrical release on cameras costing little more than a high end home video camcorder of just a few years ago. I doubt most cinema goers would realise that a camera like the F3 or FS100 was used, especially if it’s recorded to a NanoFlash, KiPro or even the new Convergent Design Gemini. However we must not forget that content is king, not the technology that makes it possible.
PMW-F3 and Stills Glass, some observations.
I have been using my F3 with a range of stills lenses via the MTF F3 to Nikon adapter. Overall everything works very well and I am pleased with the quality of the images I have been getting. However the use of stills glass is not as easy as using dedicated PL lenses. The main issue for me is iris control. With a PL mount lens you have a nice big iris ring so you know exactly where your exposure is. With some of my stills lenses I do have a traditional iris ring and with these lenses all is good. But as so many DSLR’s these days have electronic iris control many of the lenses I have don’t have an iris control ring. Mike Tapa’s adapter can control the iris of a Nikon DSLR lens by moving the blade that controls the shutter on the rear of the lens, but there are no markings or any way way of knowing what the iris is set to. This makes judging when to use more ND or where you are regarding DoF impossible to judge other than via a monitor. You can’t tell whether you are operating the lens at it’s optimum settings. In addition many of the Nikon DX lenses don’t have calibrated focus scales, so again it all comes down to guess work and the monitor.
With well designed stills glass things work well. My older Tokina 28-70 AT-X pro works very well with an accurate focus scale and proper iris control. My Nikon 50mm f1.8 manual lens and Tokina 28mm f2.8 lens also work nicely, but the Nikon DX lenses I have are far from ideal. I’m considering getting a set of Zeiss ZF.2 stills lenses as these appear to be very good lenses. I really need a prime in the 85mm range for interviews and portrait type shots.
The focal lengths I use the most are: 28mm, 50mm and 70mm. I would use a bit longer if I had the right lens. I don’t use the 18mm very often except for panoramas and landscapes.
So…. PL would be nice, but at the moment my budget won’t stretch to that. The Sony kit lenses are certainly great value for the money, but really 35mm isn’t wide enough so I would have to add a wider lens anyway. Stills glass can produce great results, but is not quite so user friendly.
Convergent Design Gemini 4:4:4 Recorder and Monitor… Yum Yum!
Well here it is. I’ve known about this rather amazing device for some time, but have been under NDA. I see this as the perfect companion for Sony’s PMW-F3 and with a street price of around $6,000 it’s a bit of a bargain. It is both a 4:4:4 uncompressed recorder and a rather handy monitor (it will do 3D recording and monitoring too), all in a single unit that is no bigger than most high end HD monitors. It records to readily available, cost effective SSD’s and can even make dual recordings to both drives giving an instant backup. It records uncompressed, so you get the absolute best quality possible. If you need an alternative codec then you simply transcode to your chosen codec when you ingest the material in to the edit system. When will it be available? Well CD are hoping to start shipping at the end of July, but that may slip a little, still it should not be too long to wait. Here are some of the headlines from CD’s press kit:
“Gemini enables videographers and cinematographers to capture at the ultimate video quality, in a small, low-power, lightweight package, at a very affordable price. Gemini features a built-in high-brightness 5.0” 800×480 24-bit LCD touch-screen for monitor and playback, and introduces an industry first – the ability to simultaneously record to two removable solid-state drives – creating instant backups; an invaluable insurance against lost footage, as well as, opening new workflow options.
Building on, but not replacing, the highly successful nanoFlash, Gemini records 10-bit uncompressed 4:4:4 / 4:2:2 video in most popular HD/2K/3G formats, including 1080p24 and 1080p50/60, with up to 16-channels of embedded audio and timecode. Gemini has slots for two removable 1.8” solid-state drives (SSDs), enabling recording in either parallel mode (instant backup), or spanning mode (longer record times). Sporting a lightweight milled aluminum case, Gemini is about the same size and weight as the popular SmallHD DP6 monitor, but includes Recording, Playback, Image Processing, Dual HD/3G SDI I/Os, HDMI-Out and consumer level audio I/O; while consuming only 8 to 15 watts of power.
Gemini features S-Log support, with user programmable viewing LUTs, which can be enabled selectively for either HD-SDI output. Flexible recording options, include simultaneously recording native S-Log video to one SSD (for on-line), and the same footage with burned-in LUTs to the second SSD (for faster creation of off-line proxies and/or H.264 video for mobile devices/internet).
A 3D/Stereo (extra-cost) option will also be available, enabling dual-stream recording and playback in a single Gemini unit; creating the world’s smallest, lowest-power, 3D recorder available anywhere. Gemini will record independent left/right channel files, while providing full synchronized playback of two streams as well as side-by-side, 50/50 composite, or anaglyph combinations. Gemini can uniquely output 3D in multiple formats simultaneously (ie side-by-side and 50/50 composite), to aid in camera alignment and monitoring.”
SxSW – South by Southwest.
What a great show in a great town. I really like Austin, Texas. Its a fun town with lots of great music, even better during the SxSW music and film festival. I’m here in the Manfrotto booth doing demos of the Genus Hurricane 3D rig. We have a nice JVC passive display and both a pair of Canon XF305’s and a pair of Sony XDCAM EX’s. But the best bit is free beer. Yes thats right free beer, not on the Manfrotto booth but from 4.30 it’s happy hour at the show and many of the exhibitors do free beer and free drinks. Oh I wish they had free beer at NAB which is only 3 weeks away now. Tomorrow I leave Austin and head to Iceland for a PMW-F3 workshop. From Iceland its on the Dubai so a busy week ahead.
Got to play with the Manfrotto 509 on the booth and it is a really nice tripod head.
Measuring Resolution, Nyquist and Aliasing.
When measuring the resolution of a well designed video camera, you never want to see resolution that is significantly higher than HALF of the sensors resolution. Why is this? Why don’t I get 1920 x1080 resolution from an EX1, which we know has 1920 x1080 pixels, why is the measured resolution often around half to three quarters what you would expect?
There should be an optical low pass filter in front of the sensor in a well designed video camera that prevents frequencies above approx half of the sensors native resolution getting to the sensor. This filter will not have an instantaneous cut off, instead attenuating fine detail at ever increasing amounts centered somewhere around the Nyquist limit for the sensor. The Nyquist limit is normally half of the pixel count with a 3 chip camera or somewhat less than this for a bayer sensor. As a result measured resolution gradually tails off somewhere a little above Nyquist or half of the expected pixel resolution, but why is this?
It is theoretically possible for a sensor to resolve an image at it’s full pixel resolution. If you could line up the black and white lines on a test chart perfectly with the pixels on a 1920 x 1080 sensor then you could resolve 1920 x 1080 lines. But what happens when those lines no longer line up absolutely perfectly with the pixels? lets imagine that each line is offset by exactly half a pixel, what would you see? Well each pixel would see half of the black line and half white line. So each pixel would see 50% white, 50% black and the output from that pixel would be mid grey. With the adjacent pixels all seeing the same thing they would all output mid grey. So by panning the image by half a pixel, instead of now seeing 1920×1080 black and white lines all we see is a totally grey frame. As you continued to shift the chart relative to the pixels, say by panning across it, it would flicker between pin sharp lines and grey. If the camera was not perfectly aligned with the chart some of the image would appear grey or different shades of grey depending on the exact pixel to chart alignment while other parts may show distinct black and white lines. This is aliasing and it’s not nice to look at and can in effect reduce the resolution of the final image to zero. So to counter this you deliberately reduce the system resolution (lens + sensor) to around half the pixel count so that it is impossible for any one pixel to only see one object. By blurring the image across two pixels you ensure that aliasing wont occur. It should also be noted that the same thing can happen with a display or monitor, so trying to show a 1920×1080 image on a 1920×1080 monitor can have the same effect.
When I did my recent F3 resolution tests I used a term called the MTF or modulation transfer function, which is a measure of the contrast between adjacent pixels, so MTF 50 is where there is a 50% of maximum contrast difference between the black and white lines on the test chart.
When visually observing a resolution chart you can see where the lines on the chart can no longer be distinguished from one another, this is the resolution vanishing point and is typically somewhere around MTF15 to MTF5, ie. the contrast between the black and white lines becomes so low that you can no longer distinguish one from the other. But the problem with this is that as you are looking for the point where you can no longer see any difference, you are attempting to measure the invisible so it is prone to gross inaccuracies. In addition the contrast at MTF10 or the vanishing point between black and white will be very, very low, so in a real world image you would often struggle to ever see fine detail at MTF10 unless it was strong black and white edges.
So for resolution tests a more consistent result can be obtained by measuring the point at which the contrast between the black and white lines on the chart reduces to 50% of maximum, or MTF50 (as resolution decreases so too does contrast). So while MTF50 does not determine the ultimate resolution of the system, it gives a very reliable performance indicator that is repeatable and consistent from test to test. What it will tell you is how sharp one camera will appear to be compared to the next.
As the Nyquist frequency is half the sampling frequency of the system, for a 1920 x 1080 sensor anything over 540 LP/ph will potentially aliase, so we don’t want lots of detail above this. As Optical Low Pass filters cannot instantly cut off unwanted frequencies there will be a gradual resolution tail off that spans the Nyquist frequency and there is a fine balance between getting a sharp image and excessive aliasing. In addition as real world images are rarely black and white lines (square waves) and fixed high contrast patterns you can afford to push things a little above Nyquist to gain some extra sharpness. A well designed 1920 x 1080 HD video camera should resolve around 1000TVL. This where seeing the MTF curve helps, as it’s important to see how quickly the resolution is attenuated past MTF50.
With Bayer pattern sensors it’s even more problematic due to the reduced pixel count for the R and B samples compared to G.
The resolution of the EX1 and F3 is excellent for a 1080 camera, cameras that boast resolutions significantly higher than 1000TVL will have aliasing issues, indeed the EX1/EX3 can aliase in some situations as does the F3. These cameras are right at the limits of what will allow for a good, sharp image at 1920×1080.