Archive for the ‘gamma’ Category

Canon C300 – Great Reviews & Posts

Thursday, December 1st, 2011

The Canon C300 is of interest to me as a potential “workhorse” video camera (replacing my current EX3) for both cinematic projects and live events (incidentally, after having written that sentence, I reassuringly found the same phrase uttered by Philip Bloom, so hopefully I’m on the right track here).

Cinematic projects in particular can benefit from more controllable DOF and both can benefit from light sensitivity, while the live events (indoor or outdoor) in particular can benefit from latitude.  Of course these things are handy in general, but those are the occasions when I’ve felt they were lacking in the past.

The C300 addresses most things, apart from lack of 10-bit output.  Hopefully I could trade-up to that in a couple-or-three years’ time when Canon upgrade to that.  And investing in “glass” (lenses) for it is probably a better investment than external recorders (buy or hire) for my current EX3.  The price stings a bit though, so I won’t just leap into it.  I’ll definitely begin by hiring/renting.

My Canon C300 research-in-earnest begins here with a (great) review I initially heard about (via private IOV forum).  That’s the UK’s Institute of videography by the way.  Here:

The following thread at DvInfo includes rolling-shutter-provoking tests (flash, jerk-motion):

The main points about the camera (for me at least, and not in this particular order) are:

  • Ergonomics / practicalities:
    • Better (some say) than the F3.
    • Weatherproof, sensor-cooling
    • ND Filters (three) in-camera
      • Seems fairly unique in this kind of camera
    • Handy proper buttons for Zebra, Peaking, Magnified views.
    • LCD and button-panel orientate in various directions.
    • Fits on a standard DSLR rig.
      • But Zacuto supply a tailored rig.  CVP are among its agents.
      • And there’s Redrock’s inspiringly-named UltraCage.
    • Solid construction, feel and mounting threads, better than “single central bolt” like many cameras have.
    • Wi-fi adaptor transmits a low frame rate version to your computer. If the lens is set to autofocus, you can actually change the focus remotely.
      • Wifi controller is an additional item – not part of the basic package
    • Battery lasts 5 hours
  • Sensor
    • Latitude (recordable, depending on settings):
      • Quoted as “13+ stops in the field”
      • But there is uncertainty over this, since apparently <<Canon thinks that with their Canon-Log color space, the camera allows “800% overexposure… which translates to …an Exposure Latitude of 12 f-stops.” Graeme Nattress of Red disagrees.>>>
    • Less noise, moire and jello than 5D Mk.2 etc.
      • Noise & moire reduction largely result from 4K sensor + DSP to HD.
        • Moire tends to result from significant interpolation inherent in less dense sensors
    • The “less noise” hence less need for low fstops (coupled with smaller sensor than 5D) means greater DOF (the antithesis of the 5D).
      • Greater DOF is preferable at times, for practical as well as aesthetic reasons (when you want to see the background).
  • Lens Mount
    • Camera comes in two lens-mount varieties, not interchangeable:
      • EF-Mount for Canon lenses (ordinaire & “CN-E”).  This is the one for mortals like me.
        • Permits iris to be controlled via dials on camera.
        • Greater available selection of lenses (also usable on stills cameras) e.g.:
          • Telephoto: “EF 70-200mm f/2.8L USM” telephoto zoom lens and tilt-shift lenses.
          • Macro: “EF 100mm f/2.8L Macro IS USM” (article photos include an image of ants)
          • Fisheye: “EF 8-15mm f/4L Fisheye USM”
          • TiltShift: “TS-E 90mm f/2.8”
        • Image Stabilisation (IS) is reported to be good e.g. with the Canon L 70-200mm F2.8 IS Version II
      • PL-Mount: More for movie professionals.
  • Recording:
    • Resolution: HD 1080p & 720p
    • Frame-rates: variable 1 to 30 fps in 1080p mode, and 1 to 60 fps in 720p mode, 1 fps increments.  Also time-lapse and stop-motion/claymation (latter is several frames per “click”).
      • But, like F3 (and unlike FS100), overcranking requires dropping to 720p
    • It can also shoot 50i and 60i (interlaced), useful for deriving 50p and 60p in post.  Historically (e.g. for DV or HDV (Z1) footage), I have done this using freeware (AviSynth and its TDeint filter) for this, but Apple Compressor and other alternatives exist too.  Stu Maschwitz apparently covers this topic in his book << The DV Rebel’s Guide>>
    • Gamma: includes Canon’s Log Gamma.  LCD & V/F display flat and corrected.
    • Audio: uncompressed 16-bit audio at 48 khz (info from FAQ).
  • Recording format:
    • Compact Flash (over 5 hours for a 128GB card)
    • MPEG-2 Long GOP 4:2:2 MXF codec with a constant bit rate of 50 megabits/sec.
      • Philip Bloom says “It is the bare minimum for HD acquisition, but it at least reaches it.”.
      • Sample recording (MXF as stated) is available here (according to here).
      • {Does MPEG-2 imply 8-bit?}
        • Yes.  That is highlighted in several other sites e.g. this and this.  Some believe (rightly or wrongly) that this limitation is a “corporate rather than technical” decision, and a future generation will have 10-bit.
      • {What of the Log Gamma? 8-bit (is it ?) would limit its usefulness or not?}
        • Opinions differ.  Obviously the extent to which it matters depends on the scene.  Some views and image comparisons are here, for 10, 8 and even 7 bits.
          • At that link, one poster suggests dithering as a work-around to reduce banding (from any camera): adjust camera to give noise then (in post) use a good noise-reduction plugin.
      • The only Super-35 sensor camera in its price category (as of fall, 2011) that records 4:2:2 color sampling on-board.
  • Ports:
    • XLR (via clip-on monitor assembly?)
    • Time code, Genlock, HD/SD-SDI and HDMI
      • {But how many bits? 10 (as I’d hope) or still only 8?}
        • Only 8-bits, surprisingly.  It is reported that: “SDI output (is) limited to 8-bit 4:2:2”
  • Monitoring
    • RGB histogram, vectorscope and an Edge monitor (focussing)

More links:

Other Misc. Links:

Training: Den Lennie’s “Music Video” Experience

Thursday, October 27th, 2011

I attended, working on one of the camera units.  Had a great time, learnt lots, at all sorts of levels.  Even how to make good use of the Movie Slate application on my iPhone!  Link:

Sony EX3 Gamma: Cine better than Std for Colored Highlights

Friday, August 19th, 2011

Gamma in Camera: Types of Response Curve

Monday, February 21st, 2011

In principle, increasing the gamma primarily has the effect of boosting the mids.  But that simple explanation does not cover everything:

  • My experiences:
    • In cameras, selecting different gamma curves also affects the general levels, typically reducing them (not simply boosting the mids).
      • Doubtless because in a camera, the “focus” is on extending the latitude of the overall recording, to avoid blown-out highlights, as opposed to increasing the brightness of scene shadows etc.
    • In Sony XDCAM EX, the precise behaviour of the gamma has been empirically determined.
    • In Sony Vegas (version 9 at least), the 8-bits levels-space used is 0..255, as opposed to the broadcast-legal range of 16..235 adopted by most other Non Linear Editor (NLE) applications.  Thus, the lowest level generated by a typical camera, namely 16, constitutes a “mid” and as such does indeed get boosted by Vegas’s own Gamma effect.
      • A workaround might be, in Vegas, to apply Media FX to expand the levels range of the footage to 0..255, do all editing at that range then for the final delivery render, compress (linearly) down to 16..235.

In a linear space, a typical camera response curve is an S-curve where the bottom curve of the “S” is relatively short and the top curve of the “S” is long and drawn-out.  So the camera is sensitive to low-light and then saturates early-on in high light.  Presumably, if all we did was to alter gamma, then the bottom-part of the “S” would shorten (the response would “pick-up” earlier) and the top part of the S-curve would draw-out even more to the left, becoming even longer, tending to saturate earlier-on (with respect to light levels).  However in practice a typical camera will at the same time reduce levels prior to the gamma curve.  ???GET FORUM OPINIONS ON XDCAM EX DATA FLOW???.  The overall result is a reduced gradient.  This essentially extends the levels-range recorded while at the same time reduces the contrast range, giving a washed-out appearance.  Meanwhile, in log-space, which is meaningful because that’s how the eye perceives brightness, the overall effect of such gamma is to make the (log) curve more linear.  Presumably then the ultimate gamma curve would be logarithmic.  I found something called S-log, which sounds a bit like that, at

  • <<Its Sony’s version of shooting RAW>>
  • <<S-Log isn’t a very aggressive log curve. … most colorists just work with it as is without applying a LUT … (which can be done) with levels and gamma filters in any NLE.  A true Log encoded file, like a log DPX, or LogC from an Alexa is a bit more extreme and you’re probably better off finding a LUT to decode.>>
  • << if/when you shoot S-Log 8-bit, and you need to make it look normal or high-contrast … Then you’d be in trouble stretching that flat 8-bit image out.>>

Then at

  • <<the uncorrected image is so flat and washed out that it can make judging the optimum exposure difficult and crews using S-Log will often use traditional light meters to set the exposure rather than a monitor or rely on zebras and known references such as grey cards. For on set monitoring with S-Log you need to apply a LUT (look Up Table) to the cameras output. A LUT is in effect a reverse gamma curve that cancels out the S-Log curve so that the image you see on the monitor is closer to a standard gamma image or your desired final pictures. The problem with this though is that the monitor is now no longer showing the full contrast range being captured and recorded so accurate exposure assessment can be tricky as you may want to bias your exposure range towards light or dark depending on how you will grade the final production. >>
  • <<In addition because you absolutely must adjust the image in post production quite heavily to get an acceptable and pleasing image it is vital that the recording method is up to the job. Highly compressed 8 bit codecs are not good enough for S-Log. That’s why S-Log is normally recorded using 10 bit 4:4:4 with very low compression ratios. Any compression artefacts can become exaggerated when the image is manipulated and pushed and pulled in the grade to give a pleasing image. You could use 4:2:2 10 bit at a push, but the chroma sub sampling may lead to banding in highly saturated areas, really Hypergammas and Cinegammas are better suited to 4:2:2 and S-Log is best reserved for 4:4:4.4. >>

  • << The LOG mode … captures what the camera is capable of discerning. Because the maximum range of sensor data is being recorded at all times, there is more range to create the desired look in post. In a REC709 video gamma (in contrast), an image may have a bright light source overexpose to white and dark shadow areas record as black. The same image recorded in LOG may have considerable detail on both ends of the exposure range, which in later color correction can be exploited, if so desired. >>
  • << When footage is transferred with video gamma, it is meant for display (perhaps with minor adjustment applied later). When footage is transferred using the LOG CINEON curve, no artistic interpretation of the footage happens during the transfer – the goal is to preserve the full range of possibilities for later adjustment. This footage will look very flat and dull when displayed directly on a monitor. >>
  • <<  Most Digital Cinema cameras have a mode of recording or transcoding to a LOG curve. For example, Sony has S-Log (in the F35, F23, SRW-9000 and the PMW-F3), ARRI has LOG-C, RED has REDLOG, and Panasonic has FILMREC (which, while not technically a LOG curve, serves the same purpose). >>

  • << In a perfect world you would control your lighting so that you could use standard gamma 3 (ITU 709 standard HD gamma) with no knee. Everything would be linear and nothing blown out. This would equate to a roughly 7 stop range. This nice linear signal would grade very well and give you a fantastic result. Careful use of graduated filters or studio lighting might still allow you to do this, but the real world is rarely restricted to a 7 stop brightness range. So we must use the knee or Cinegamma to prevent our highlights from looking ugly. >>
  • << If you are committed to a workflow that will include grading, then Cinegammas are best. If you use them be very careful with your exposure, you don’t want to overexpose, especially where faces are involved. getting the exposure just right with cinegammas is harder than with standard gammas. If anything err on the side of caution and come down 1/2 a stop. >>
  • << If your workflow might not include grading then stick to the standard gammas. They are a little more tolerant of slight over exposure because skin and foliage won’t get compressed until it gets up to the 80% mark (depending on your knee setting). Plus the image looks nicer straight out of the camera as the cameras gamma should be a close match to the monitors gamma. >>
    • Great practical advice including the need to avoid fleshtones getting into the flesh region of the response curve


Gamma in Camera – Pros & Cons & Bits

Sunday, February 20th, 2011

To obtain/maintain/increase/verify an intuitive feel and hence greater confidence for the appropriate use of gamma in camera settings, I did some thinking & research.  The basic idea is as follows:

  • A typical consumer camcorder produces crisp images
  • “Film Look” use of a professional camera may employ non-standard gamma settings in the camera settings.
  • The straight results of this are images of “washed-out” appearance.  To obtain a pleasing result requires grading (levels & gamma, saturation, color curves etc.).  Example:

Regarding the second, more professional approach:

  • The immediate result is “scary” because it looks washed-out
  • The goal is not to produce an immediately-pleasing image but to capture “as much information as possible” (an often-quoted phrase) from a scene, with the intention and indeed requirement for grading.  One has to see it “through the eyes of a grader”.  A naive person (e.g. a newbie or a client) will of course not immediately see it that way.
    • Example references to this:
        • <<The RED RAW look, the washed out, flat, low contrast, incredibly versatile form in which the footage originates … screams possibility in our faces. Low contrast can, to the DP, imply power … being precious with the RED footage, and trying hard to save every bit of detail we started with.>>
        • <<I can see how the washed out look can become something in and of itself, and have people like it, and others not.>>
  • What does this mean?  In general, possibly:
    • The complete levels and color space of that scene, un-clipped (clipping destroys information).
    • Any subtle light/shade within shadows of the scene.
  • Questionable aspects:
    • Grading takes time (bad for quick-turnaround jobs) and if written to intermediate files (e.g. prior to editing) then it can also eat disk space.
    • There is a trade-off between generality and specificness.
      • Capturing maximum information provides the grader with greatest freedom.
      • On the other hand if it is known in advance that crushed shadows are required, e.g. to obtain silhouettes / film noir effects, then it is a waste of effort / bits if not counter-productive to boost them in the camera.
    • The degree to which grading can be applied in practice depends on the levels and color space resolution of the camera.
      • Prosumer cameras such as Z1 or XDCAM-EX record to 8-bit levels resolution.   And then only a sub-part of that levels-space (typically 16..255 or 16..235, depending on camera and settings).
        • For cameras whose sensors work at greater resolution (and can output this information) there is the option to record to external devices at that greater resolution (e.g. 10 bits 4:2:2).
      • While it is possible to apply effects like levels, gamma or color-curves (S-curves) to “professional” washed-out imagery, beyond a certain degree, the image will appear ragged or flesh-tones will appear sunburn etc., as the gaps between successive values of the bit-space get stretched too big.  One can actually see the gaps (between striations) in a Waveform Monitor (applied to the result of grading).
        • In that case we have in fact lost information, defeating the original goal…
      • If the results of grading are pretty-much identical (or, from the previous point, possibly inferior) to what would have been obtained in-camera using a more standard setting, then what was the point?
  • Reassessment:
    • Due to the trade-off issues, the real goal should be to record the maximum relevant information.   In other words, to be a little bit specialised.
      • This is the logic behind employing physical filters on a camera, such as grad filters (“sunglasses” e.g. for the upper – sky – part of the image).
      • Even on feature movie sets I have come across formal instructions for film cameras to be deliberately “pushed a stop or two”.  Committing at record-time to something that could, presumably, have been achieved equally-well in post, which itself can be done almost immediately based on HD footage recorded simultaneously from HD cameras attached to the main camera.  I have seen directors receive rushes and quick cuts from such cameras within seconds…
    • The degree of commitment/specialization may depend on the type or uncertainty of the scene and on the consequence of making a mistake.  Feature films are very planned and their shooting is very iterative.  On the other hand there can be one-offs such as special-effects or VIP moments.  At the other extreme may be live events where anything can  happen – subjects, lighting, over-bright/over-dark etc.
    • The missing factors in the “maximum information” principle are then:
      • Relevance – what kinds of information are relevant?
      • Resolution limitations.
        • If we only have 8 bits, then what is the practical limit of grading?
        • Conversely, if we need to maintain maximum latitude etc., when do we need more than 8 bits (in practice mostly 10 bits)?

XDCAM-EX in-camera compensation for Tiffen T1 “green tint”

Monday, August 30th, 2010

Great article:

    • “(These are) picture-settings that are tailored to my personal taste, with post-processing in mind. I’ve been able to use shots right out of the camera without the need for CC, but it does ask for contrast adjustment to taste.”
    • “…the matrix corrections in the first profile are to compensate for the green hue the IR filter casts, even after taken a white balance. I use the fluorescent light matrix, simply because it does exactly two things to the picture (and in measurements) that this specific camera demands; it remove the “green Sony hue” and it is the lowest-noise matrix. It shifts the colour balance towards red/magenta, removing the green hues and preventing your cast from looking terminally ill.”
    • “I use Cine 1 gamma almost exclusively because it’s clearly the most lownoise gamma. I sometimes use Cine 4 indoors with low / existing light. …adjust Gamma on a per-scene basis.”

XDCAM-EX Gamma Settings

Monday, August 30th, 2010

I worried about and noticed in practice an effect where if I was using CINE gammas on the XDCAM-EX and exposed for faces at 70% (by zebras) then the gamma rolloff would result in “pasty-face” appearance.  It does …and did…  The solution for good looking faces is one of the following:

  • Under-expose in shoot, raise in post.
  • proper-expose in shoot, use standard gamma (not cine gamma), be careful not to let the face hit the knee (?) e.g. set knee to 90% or 95%.
  •  take a given gamma curve (or even a flat standard one) and tweak it using gamma level & black-stretch adjustments etc. until it fits the scene.


FCP inherent (unwanted) level & gamma changes – unlike Avid’s AMA

Monday, August 30th, 2010

Someone noticed that XDCAM-EX footage imported to FCP appeared different as compared to Avid (AMA import).  Addressed in an Avid forum thread started May 2010, referring to FCP 6.06 and Avid 4.02:

  • What AMA gives is, is _exactly_ what the camera has captured. What FCP shows you, is a remapped image, most often with a gamma shift. 
    • (For Avid AMA imports, Avid settings for RGB or 601 etc. make no difference – it’s always as-recorded).
    • … imports (to FCP) will look different (to expected), because FCP/QT “corrects” the gamma when bringing in footage (even if you would not want that).
  • Most people seem to agree that FCP works in 0-235, not 0-255, not 16-235. And without the option to leave things untouched. So if you import something into FCP, there’s no getting it back to the original levels anymore.

I guess I’d better do some experiments with ramps & scopes etc…

DNxHD & Windows/Mac Issues

Saturday, July 24th, 2010

Gamma-shift issue:

    • “QuickTime movie, created with Avid on a PC, using the DNxHD codec. When I open it in QuickTime Player on a PC, the colours are fine, but when I import it into Final Cut on a Mac, the colours are a lot brighter- gamma shift”.
    • I have ProRes and DNxHD clips of the same thing on the timeline. When I switch from a frame in one clip to the same frame in the other clip, there is a very visible difference between the two. The DNxHD version is brighter and ‘milky’.  I’ve tried exporting DNxHD from Final Cut and it has the same problem as the DNxHD sourced from the Avid.”
    • “It’s the codec. DNxHD reports RGB values to FCP not Y’CbCr. Therefore FCP applies its internal RGB interpretation which causes the gamma shift you see.”
    • “Any non native codecs to final cut pro should be transcoded first through compressor; best way to check if the gamma has shifted is take an image with tonal ranges which vary over a gradient e.g. sky; look at the scopes in avid for the dnx file; look at the scopes in final cut pro for the dnx file; no guess work”
  • x

PC Windows <--> Mac OS X RoundTrip (Round-Trip)

Monday, July 19th, 2010


  • In Windows I export from Sony Vegas to AVI (CineForm).  In OS X I read the file into FCP and apply the SmoothCam effect, then export to ProRes.  In Windows, Sony Vegas, I replace the original file with the smoothed one.  The levels/gamma are wrong.

Solution (Search):

  • Sony Vegas forum
    • Use DNxHD
      •  Couple of tips re DNxHD:  709 color level assumes 16-235, and RGB assumes 0-255.
    • Force it back again:
      • But this presumably implies getting re-quantized twice (the roundtrip issue and the forcing), which for 8-bit footage I imagine could reduce the quality (banding).
  • Uncertainties
    • Where and how does this gamma get applied?  In FCP I didn’t (knowingly) alter the levels (eg until it looked right), I just applied the SmoothCam filter.  So I guess it would look wrong on the (pre-SnowLeopard) Mac but I wouldn’t care.  Wouldn’t FCP then export back whatever it got but smoothed?  This one is really confusing.    Experiments needed (when I get time…) I guess.

FCP Levels & Gamma Conventions e.g. for Stills

Friday, February 19th, 2010

Things To Remember []

  • Still images are RGB in a 0 to 255 range
  • Levels above 100% FCP, 100 IRE or code 235 are called “super white”
  • Final Cut Pro automatically converts images to fit into the 0% FCP to 100% FCP range when it is set to “White”.
  • Final Cut Pro automatically converts images to fit into the 0% FCP to 100% FCP range when it is set to “Super White”.
  • Final Cut Pro only looks at the 0% FCP to 100% FCP range upon still image export, and maps this range to 0 to 255 RGB.
  • Picture information can be lost on still image export if you have picture information in the 100% FCP to 110% FCP range.
  • Final Cut Pro always applies a gamma correction of about 0.8 to imported still images. If necessary, this can be corrected by applying a gamma correction of 1.2 in Final Cut Pro or 0.8 in Photoshop.
  • Don’t preempt Final Cut Pro’s conversion of still images by setting your blacks in Photoshop to 16 and whites to 235. Final Cut Pro expects you to use the full 0 to 255 RGB range.
  • “White” and “super white” settings only effect the import of still images.
  • “White” and “super white” settings do not effect video or video rendering.