The waveform monitor in the GH5 seems to be incorrectly calibrated in Vlog mode. The waveform display never exceeds the second dashed line below the solid top line. Increasing exposure from a normal level shows compression and hard clipping at the second dashed line with no transients above. This observation suggests that the second dashed line corresponds to 1023 bits.

Has anyone compared the internal GH5 WFM display with an external monitor?

This is sounding very much like the same queries relating to the GH4 a while back. Check out Adam Wilt's V-Log article surrounding these levels issues. I think it will give you some pointers.

Not dissimilar to working with S-Log on the Sony cameras with their white levels of 59 and 61 depending on whether it's S-LOG 2 or 3. Which in turn means your skin tone levels also come down.

On the GH5 you can display a 709 LUT to the screen:

"Select “V-LogL View Assist”
Select “LUT Select”
Then choose “Vlog_709”

I haven't checked but does this LUT not re-scale the WFM levels?

For example on the some of the Sony's when you monitor via their Rec 709-800 LUT it re-scales the WFM to your more standardized 70 IRE skin and 90 IRE peak levels.

https://www.provideocoalition.com/v-log-l-on-the-gh4-don-t-panic/

Chris Young
CYV Productions
Sydney

The waveform monitor in the GH5 seems to be incorrectly calibrated in Vlog mode. The waveform display never exceeds the second dashed line below the solid top line. Increasing exposure from a normal level shows compression and hard clipping at the second dashed line with no transients above. This observation suggests that the second dashed line corresponds to 1023 bits.

Has anyone compared the internal GH5 WFM display with an external monitor?
The waveform is correct, V-LOG-L is ranged between 7.3 and 80 IRE which translates in to 10 bit code values of 128 and 765

Right.

So it is just a matter of understanding this and exposing accordingly. Which is exactly the same as on the Sony's if you are running your own 709 monitoring LUTs the WFM levels you are seeing are reflecting the true LOG exposure levels.

Thanks good to know.

Chris Young
CYV Productions
Sydney

Thank you for your explanations of V-Log L levels.

It seems to me that the WFM display as implemented wastes space on the EVF in V-Log L mode. The waveform will never enter the top third (roughly) of the WFM display but the virtual graticule remains overlaid on part of the image. Perhaps a 0 to 100% scale (765 code value) would be more useful with lines to represent 90% diffuse white and 18% grey. A relational display of this type could also be used for HLG when it becomes available on the camera. The 100%, diffuse white and grey lines would have to be matched to the HLG curve.

Fiddling with the display as suggested may complicate use of the GH5 in multi-camera settings but the relational display should help the large number of users who shoot single camera.

You're not looking at the specular transients.

In Resolve:

Color Science to ACES.
No input transform.
No output transform.
Luts disabled.
Bypass all grades.
Waveform monitor brightness full. (So you can see the transients)

V-Log-L transients are written to code value 965 and may even go higher. You have to consider the signal to noise ratio for specular highlights is not identical to the saturation level.

The waveform monitor in the GH5 LCD/Viewfinder is coarse and not showing you the specular transients.

My Sony F55 in S-Log2/3 behaves similarly.

You're not looking at the specular transients.

In Resolve:

Color Science to ACES.
No input transform.
No output transform.
Luts disabled.
Bypass all grades.
Waveform monitor brightness full. (So you can see the transients)

V-Log-L transients are written to code value 965 and may even go higher. You have to consider the signal to noise ratio for specular highlights is not identical to the saturation level.

The waveform monitor in the GH5 LCD/Viewfinder is coarse and not showing you the specular transients.

My Sony F55 in S-Log2/3 behaves similarly.
Sorry Tom but you are wrong.
V-Log does extend beyond this but V-Log-L does not.

Make sure you explicitly set the clip attribute to data levels otherwise Resolve interprets the clip as video levels.

Hi Cary,
Levels were set to data explicitly. If you are looking at the code values anywhere else but inside the written mp4 files it will clipped. For example, if you monitor Log levels over hdmi, you are only seeing log inside broadcast 2.2 - 2.4 gamma. Levels will be clipped. If you are recording log externally that way, recorded levels are also clipped.

Hi Cary,
Levels were set to data explicitly. If you are looking at the code values anywhere else but inside the written mp4 files it will clipped. For example, if you monitor Log levels over hdmi, you are only seeing log inside broadcast 2.2 - 2.4 gamma. Levels will be clipped. If you are recording log externally that way, recorded levels are also clipped.
Sorry but this is just nonsense, you are simply wrong and apparently have a hard time admitting it!

Did you even try your own suggestion using ACES?

Here is a screen shot using the GH5 in V-Log-L fully blown out, using ACES with all transforms at bypass.

And here is one with minimum exposure.

As you can see code values range between 128 and 768, as designed!

Cary, the sensor is in saturation when the whole image or a large part are blown out. The transient peaks of a properly exposed image are not limited to 765 by VLogL. When the sensor is in saturation, it will only write up to the code value of the sensor saturation point.

Cary, the sensor is in saturation when the whole image or a large part are blown out. The transient peaks of a properly exposed image are not limited to 765 by VLogL. When the sensor is in saturation, it will only write up to the code value of the sensor saturation point.
More nonsense!
I give up, there seems to be no point arguing with you!

Cary,

The GH5 is recording specular highlights above 80 IRE, the waveform monitor is clearly showing this. If you clip the entire sensor then yes 80 IRE.

The attached V-Log-L 10 bit 422 image has bypassed grade, no lut, no idt or odt.

https://drive.google.com/file/d/0B7wNrNfr-UB4XzlDU0xKeVVIYUU/view?usp=sharing

If you upload the out of camera clip I will take a look at it.

You may have inadvertently setup all kind of things in the Color Management page (transforms, LUTs) that misleads you in thinking V-Log L is not limited at 80IRE.

Here is a DCTL to see what, if anything, is coded at or above 80IRE (full range):

__DEVICE__ float3 transform(int p_Width, int p_Height, int p_X, int p_Y, float p_R, float p_G, float p_B)
{
const float min = 0.8f;

const float r = (p_R < min ? 0.0f : p_R);
const float g = (p_G < min ? 0.0f : p_G);
const float b = (p_B < min ? 0.0f : p_B);

return make_float3(r, g, b);
}

Replace min with .75f for 80IRE full range equivalent.

What noise level do you select for V-Log L in camera?

Attached is download link to 6 seconds of VLog-L 2160p30 10 bit 422 straight from the GH5.
Also attached is screen capture of WFM at 03;16. Data level = full. Note the range is 85-940.

Scrub to 05;24 and toggle forward and back one frame. There is a focus shift at that point, You will see the peak level collapse from 925 or so to 768 as it goes out of focus. This implies that yes, 80 IRE is a soft limit, but high pass filtering permits specular highlights above 80 IRE. So I was surprised to see you asking what NR setting because I was about to suggest you set yours to -5 which is in fact what the attached video is set to.

https://drive.google.com/file/d/0B7wNrNfr-UB4ODZCcmFhdTlBalU/view?usp=sharing

https://drive.google.com/file/d/0B7wNrNfr-UB4b1BhQkN4d1NBcG8/view?usp=sharing

Thanks for posting!
Thinks are certainly not as straight forward as I thought!

You say that high pass filtering permits specular highlights, but what if what we see is either noise or encoding artifacts?

Noise at -5 may suppress valuable noise reduction that cannot be reduced in post. I do not know the internals of the GH5 but I would assume that noise reduction takes place right after the sensor readings and certainly before it goes into the encoder. I would argue that reduction before encoding can be much more efficient than after encoding because it can operate on sensor data and before debayering, assigning a color space and applying chroma subsampling, also encoding efficiency is negatively influenced by the amount of noise in the video.

I attached a clip using the above referenced DCTL to see what is actually above 768 (looking at the RGB code values not the actual luminance).
There is a clear edge and the inside looks like DCT patterns.

I would assume the inside of the lamp is the brightest and not the surface.

Here is the same clip filtered by 80 IRE actual luminance:

All that could be true. All I was ever saying was that I knew VLog-L was writing code values above 768 (and below 128 as well).

But that small difference between 768 and 940, for HDR (which is all I do), once IDT transformed in ACES to Panasonic V35 and ODT to ST2084-1000 represents a difference in display referred specular brightness of about 400 nits, no small amount. The GH5 is only marginally adequate for HDR anyway, and if the specular highlights are suppressed loses the je ne sais quoi, looks sterile. In HDR, we're only trying to emphasize specular highlights, not blast the viewer with overall display brightness.

So the choice to use NR is yours.

And you were right about that, it does write above 768!
Question remains for me is that data we should actually use.

It is indeed no small amount.
I certainly would hope the GH5 would have usable values above 768.

Thank you for putting this to the attention of everyone and I am sorry for my harsh words!

You guys just gave me a headache......just to much info for my few remaining brain cells. Can't I just push the record button?

No problem Cary, it is a good discussion! Now we need for to you to tell us at what level of the NR filtering detail becomes noise.

You guys just gave me a headache......just to much info for my few remaining brain cells. Can't I just push the record button?

If you aren't concerned about punching a hole in the universe, then yes.

Here is the same clip filtered by 80 IRE actual luminance:

This is *REALLY* cool.

I did some small testing to see how both the noise and the sharpness settings influence the spikes above 80IRE

From largest to smallest spikes:

Sharpness: 0 Noise: -5
Sharpness: 0 Noise: 0
Sharpness: -5 Noise: -5
Sharpness: -5 Noise: 0

Sharpness seems to be a bigger factor than noise.

My current settings are Sharpness -5, Noise 0.

Well that's interesting!

As the narrators in the old westerns used to say " Meanwhile, back at the ranch", I was investigating the V-Log L clip point on the GH5 waveform monitor. I took a simple approach using manual exposure and locking the white balance to 'cloudy'. I only adjusted f-stop, first finding the value that didn't cause clipping on the WFM. I set the camera in record and narrated what I was doing and seeing. I opened up the aperture and described the extent of clipping for each stop.

I followed the recommendations about configuring Resolve and started looking at the clips. Two scenes produced interesting results. I used an ornamental white turtle sitting on my deck as one subject. The turtle occupies about 30% of the width of the screen at the centre. The turtle has coarse details on the shell. I shot from the top looking down. As I increased the aperture, the GH5 WFM clipped on the second dashed line below the main solid top line. On the Resolve WFM, the top of the clip falls right on the 768 line and holds while the background levels move up with a larger aperture. There is a bit of 'fuzz' on the top of the hard clip.

The other scene is shooting upwards through trees leaves and branches, and shows the roof line and chimney of a house. The sky was high white haze. The GH5 WFM showed the same kind of clipping as the turtle shot when I increased the aperture. Now it gets interesting. The beginning of the clip (f13) brushed the 768 line on the Resolve WFM with a fuzzy edge going above the line. At f10, the GH5 WFM showed clipping but Resolve WFM had transients over 832. At f6.3, no sign of clipping on the Resolve scope with transients visible at 896. The main waveform was solidly over 800 where the bright sky was most visible.

I decided to investigate the trees and branches scene more closely. The sky was uniformly bright behind the trees due to the high overcast. I used a power window to isolate a portion of the image where the sky was the primary feature. I used the curve to set areas outside the window to 0. The WFM showed the corresponding area with a distinct flat line at 768. The branches and leaves are creating values above 768 but the sky is clipped. I moved the window around the screen to find peaks. In areas where the leaves and sky occupied similarly sized areas the peaks were visible. I don't know if they are the result of a low pass filter driving the clipper or if they come from artifacts, possibly from edge sharpening. Considering that a major goal of HDR is to preserve speculars, it makes sense that the clipping mechanism would allow finer detail to pass with less attenuation.

A third shot was red flowers. As I opened the aperture, the red channel viewed on Resolve started to clip around 800. The clip looked softer than the sky but the flower petals were not a uniform brightness so a bumpy edge of varying intensity makes sense.

The processing in the GH5 going into the V-Log L profile seems anything but simple. However, if the GH5 WFM is not clipping then the image is probably suitably exposed with bright transients protected.

If you aren't concerned about punching a hole in the universe, then yes.
Hmmm, that might be a real trip!

There is a chance that im totatly wrong here but I'll toss this out for anybody to confirm or correct:

Its my understanding that VLog is a fixed gamma like Cineon and Sony SLog-3. (Slog-2 is not fixed but individually mapped to each sensor model)

If this true, than VLog itself is not clipping or maxing out at 80 IRE. VLog does not place this limit in any way. (Aside from it's normal gamma compression nature) Its actually THIS particular GH5 image sensor not being able to deliver a significant signal over 80 IRE inside VLog with the exception of stray highlights or noise or whatever.

VLog is simply taking all the dynamic range the GH5 sensor can feed it. Obviously, the VLog bucket or curve still has lots of headroom leftover above 80 IRE "if" the image sensor were able to produce it.

So "maybe", if im not wrong, its really the GH5 sensor that cant output anything significant registering higher than 80. In theory, if the GH5 had a 14 stop sensor than we'd be looking at over 90 IRE in the same exact VLog curve.

I dunno. Does this make sense? All the numbers we are talking about here are not really "VLog" numbers, they are more like "image sensor" output numbers.

I think you must separate V-Log encoding from camera video pre-processing. I think the requirements for a consumer camera are significantly different than a professional camera.

The GH5 is a product of Panasonic's consumer division, not the professional camera group. The camera is meant to be sold to hundreds of thousands of customers, many of whom will have a casual interest in videography and little technical knowledge. The GH5 must be consumer friendly and play nicely with regular consumer televisions.

High dynamic range television sets are just beginning to establish their place in the market. Consumer sets are only capable of limited HDR performance because the power supply in the set limits the total area of the display capable of achieving high brightness at any given instant. In practical terms, the set can deliver full screen area brightness up to the usual level for SDR (100 nits) plus limited area highlights (100 - 1000 nits). These limitations are not a severe problem as most of the highlights come from specular reflections or point sources at night. HDR can deliver a night street scene with good detail in the darker areas while traffic lights and neon signs are rendered in bright, saturated colors.

If a company wants to deliver an HDR consumer camera that works well with consumer HDR displays then it must deal with the issue of highlight area versus brightness. The simplest approach might be to use a scaled variation of the camera's normal SDR processing to keep large areas in check and separately high pass filter the video to create the HDR details that can be added to the SDR portion of the image. The resulting HDR signal can be encoded into HLG or V-Log L formats.

A professional camera designer would have no reason to take display limitations into consideration for high V-Log levels. Recorded images are going to end up in the hands of a colorist who will adjust them to match the capabilities of the target display device. Only one kind of V-Log decoder is needed in an edit program because the code values have the same meaning in V-Log or V-Log L.

I have no knowledge of the video processing that Panasonic is using with the GH5 so please understand this is all theoretical. I am simply trying to match my observations of GH5 V-Log L signal behavior from with a possible explanation.

Its my understanding that the way V
log, Cineon and SLog-3 works is this:

Take whatever image sensor you have. Take a certain gray point on its output and map it to the proper coordinate gray value inside these log curves. Then, however far up and far down your sensor output acheives...the total dynamic range that it produces.....will land at whatever waveform points that it does. (High and low)

So, if have a 12 stop sensor, your sensor can only hit about 80 IRE. If you had a 10 stop sensor, you could maybe only produce a 70 IRE value. If you had a 15 stop sensor, you might be able to tickle 100 IRE on these log curves. What im saying is that your sensor is calibrated at a certain "middle-ish" grey point with the shadows and highlights falling where they naturally would on the curve/scale.

Now this is all very different in Sony SLog-2. For this log, Sony went a different direction. I am told that Sony maps SLog-2's curve based on each sensor models maximum highlight and shadow output. They map each sensor's shadows right down to almost the bottom near 0 IRE and take the sensor's maximum brightness all the way up to 109 IRE. So Sony uses the entire scale for each sensor, no matter if its a 10stop sensor or 11 or 14 stop sensor. Every sensor will be "stretched" to a max 109 value.

This is why SLog-2 is not as flat as SLog-3 and is more "8bit friendly" than all the other log curves out there. SLOG-2 uses the full 8bits for recording and does not leave any headroom unused no matter what the sensor's actual dynamic range output it has.

Technically, SLog-3, Cineon and VLog can hold over 16 stops of dynamic range even though most sensors today cant truely do 16 stops. So, as sensors get better and better, we should see highlight clipping points rising further and further up the waveform scale until we eventually hit VLog 109 IRE. But not with the chips today.

Another way to say it is, if you drop a 12 stop GH5 sensor into the middle of a 16+ stop gamma curve, you will get literally 4+ stops of unused headroom. Even more unused headroom for lower dynamic range sensors and will look even more dismal on your scopes.

This is the best I can explain with my limited knowledge on this. I have spent allot of time with Sony's guys at NAB over the years and this is what I have been told. I believe this is all basically accurate. If not, lemme know.

CT

I agree with what you are saying for a professional camera, but the GH5 is a consumer camera. I think Panasonic is pre-processing the video to achieve compatibility with consumer HDR sets. We will know more when the summer update is released and HLG becomes available. My bet is that after decoding in an edit program, HLG and V-Log L files will look the same.

Going back to the original subject of Waveform Display Calibration, I don't think it is possible to actually see the HDR component of the signal because the display is too coarse as suggested in one of the earlier posts. As it is, the WFM doesn't help with the HDR levels and reduces the value of the display for SDR levels. Configuring the WFM to display the SDR levels full scale would make more sense.