What some people are calling IRE is really just the percentage on the RGB scale, where (0, 0, 0) is the black point and (100, 100, 100) is the white point. We use percentages because there are different ways of encoding RGB values, and we want to specify the RGB values without regard to any particular encoding. The code values of black and white will be different depending on what RGB encoding you are using. E.g., Rec.709 specifies a couple of ways of encoding RGB values (8-bit and 10-bit Y'CbCr). H.264 adds another (video_full_range_flag). HDMI has a few different encodings. There are multiple common RGB encodings, too, like floating point or integer with different ranges. But every one of those RGB encodings defines the code value for black and the code value for white and the ranges used, so that code values can be translated to and from an RGB percentage.

For cameras that record internally to a log color space, the RGB encoding is almost always Rec.709. Sony S-Log, Canon Log, Arri Log C, and Panasonic V-Log use Rec.709. GoPro Protune is the one exception I know of.

IRE is a scale for voltage in analog video systems. It is absolutely well defined, in IEEE standard 205-1958. IRE is defined in terms of the blanking level and the white level. It can be related to percentages on the RGB scale, if you also say which analog standard you are using. For analog HD video standards, IRE is equal to the RGB percentage. For analog SD video, they are not equal, depending on which country's analog standard you use. But these days everything's digital, so it's rather pointless to talk about IRE. The different manufacturers have not been consistent about dropping the outdated term.

V-log will be great for people using external 10 bit recording. 8 bit video has been a problem since the early 1990's when 10 bit became the accepted minimum for doing video effects work to avoid visual artefacts appearing during compositing many passes on digital tape. This whole issue has more to do with bit depth than where the log recorded black and white levels appear on an IRE scale.

BTW IRE is a simple 0-100% scale of bit 16-235 (8 bit) or bit 64-940 (10 bit) as defined by the rec601 and rec709 broadcast standards.

Most manufacturers are trying to move forward with new standards but must also remain compatible with existing broadcast standards.

I have done extensive tests with my GH4 using the 16-235, 16-255 & 0-255 settings to see how these settings were interpreted by Avid Media Composer, FCP7, FCPX, Adobe Premiere & Autodesk Smoke, all on Mac OSX. The only setting which mapped levels correctly on import to all those applications was 16-235. Theory is fine for discussion but nothing beats real-world practical testing with technical knowledge and accurate measuring instruments.

I will be VERY interested to see how 8 bit V-log holds up when pushed hard in colour grading software. Until I test it, it's just talk.

@Vitaliy_Kiselev

As one of the explanations of this option that I found is that it is flag that tells H.264 decoder to scale actual data that are in 16-235 range into 0-255 range.

Yes, and in the case of V-Log-L encoding, it's the limits it imposes on the scaled 8-bit output of the decoder that degrade the quality of the image. With V-Log-L on a 8-bit codec, the decoded output data will be limited to the range of 32-182, only about 7-bit precision. Regardless of how the YUV data is internally encoded within the H.264 macroblocks, the decoder will not produce any more image detail than that.

In my experience, 8-bit H.264 was just barely detailed enough to handle the GH2's 10-stop dynamic range with high image quality, but that was after the camera was hacked to record at 100Mbps. I seriously doubt the GH4 can squeeze 12-stops of dynamic range without visible degradation into something closer to 7-bit precision, regardless of the camera's increased bitrates.

@Vitaliy_Kiselev

Yes, 16-235 studio-swing is the default standard for 8-bit Rec 709, but the standard also supports optional bitstream metadata flags that can be used to indicate 0-255 full-swing data. The GH4 supports this feature with a user-selectable option. When decoded, a full-swing H.264 stream will produce 8-bit data ranging from 0-255.

Some more charts (they look different because of x axis difference)

The function for converting from linear signal to V-Log data is as follows. With linear reflection as “in” and V-Log data as “out”,

out = 5.6*in+0.125 (in < cut1 )

out = c*log10(in+b)+d (in >= cut1 )

cut1 = 0.01, b=0.00873, c=0.241514, d=0.598206

This is from their PDF, and they use again "reflection" term instead of simple "sensor raw value".

IRE is not rubbish. It measures luminance values in the decoded video signal which allows us to measure display brightness without referring to bit depth.

OK, how about using simple percentage in this case (0-100%) ? As all IRE complications came from reality we had with analog signal.

Is it possible that when in V log mode, GH4s exposure meter and zebras will be programmed to recalibrate for accurate V log exposure metering as part of the new firmware? I am thinking for example of BMPCC - in camera zebras are calibrated for it's own film log right? and so I expose shy of zebras clipping at 100% for all important highlights and this works fine when there is sufficient light, gives me maximum safe exposure. Why should GH4 V log be so much more difficult to use? Guess time will tell where the zebras need to be set to protect important highlights

Shooting log rules topic needed.

LOL

If you overexposure the footage beyond this point, its dynamic range will no longer match the calibration of the LUT and the results will be inaccurate, particularly in the non-logarithmic 4-stops of shadow detail range. Used in this way, V-Log-L becomes a subjective flavoring, like any other built-in profile.

One thing I am amazed is how much stuff can be made from extremely simple math thing. If you start adding um smart words.

@Brian_Siano

[With V-Log-L], if we expose a stop or two more brightly than we normally do, those extra stops shift down and enable us to gain more detail in the midrange and lower ranges.

As with all log profiles intended for use with a calibrated LUT, V-Log-L is designed to be used at exactly one specific exposure - with highlight clipping at 79 IRE. If you overexposure the footage beyond this point, its dynamic range will no longer match the calibration of the LUT and the results will be inaccurate, particularly in the non-logarithmic 4-stops of shadow detail range. Used in this way, V-Log-L becomes a subjective flavoring, like any other built-in profile.

Full well capacity doesn't change because of V-Log L. Panasonic was not throwing away tons of highlight range captured by the sensor in the days before V-Log L.

Well, as they openly state, they did throw out stuff, just read release notes.

Why do you think V-Log L is not available at the same base ISO as standard photo styles?

What exactly is "base ISO" in your understanding?

Because for the same ISO setting, it uses a lower gain, and of course there is a minimum gain. I don't like to debate with you. Just think about it.

I think you are utterly confused. It is not a debate, just describing how thing actually works, it is not magic.

Actual pixel at sensor collects charge as result of photons hitting it. Hence it depend only on exposure time (with same scene, lens and all). Sensor has analog gain (>=1.0) before ADC. As any amplifier is not ideal, it adds some noise (to the heat noise and some other sensor noise). And ADC produce raw values (they are also being corrected to reduce fixed pattern, and other things).

VLOG or any LOG format is just another function transforming raw values into image. Mathematically it is different, but it is works on same place as all the normal modes.