EX1R - HDMI output 8bit or 10bit?
 

Can anyone confirm the bit depth of the EX1R's HDMI port?

We know that it's SDI is 10bit but can we assume that it's HDMI output is the same?

also, I could very easily be wrong about this but I was told by several people that the general HDMI spec for all video devices only supports an 8bit color space.

I'm looking into getting an Atomos Ninja and I'm hoping I can grab true 10bit video of my EX1R's HDMI port.

CT

Re: EX1R - HDMI output 8bit or 10bit?
 

8 bit HDMI and HDSDI. It is an 8 bit camera.

But the color space is 422 on HDSDI and HDMI.

The EX codec is 420.

Re: EX1R - HDMI output 8bit or 10bit?
 

That's not correct Olof.

The HDSDi output of the EX1 and EX3 is 10 bit.

I have no idea what the HDMI output is. However the EX's are a little on the noisy side so any advantage that recording in 10 bit may give is likely to be lost in all the noise. It will be the image noise that will govern how far you can grade, not the bit depth, unless you have a very quiet camera like the F3.

Re: EX1R - HDMI output 8bit or 10bit?
 

I read from a link in dvx.com that output from hdmi port of ex1r is 10bit, but i want some independent confirmation from probably sony or the likes.Maybe Alister Chapman can help in that direction.

Re: EX1R - HDMI output 8bit or 10bit?
 

I wouldn't get too hung up on whether it's 10 bit or 8 bit because it really isn't going to make any difference whichever it is given the EX1R's noise figure. You just won't gain any advantage recording 10 bit over 8 bit with a noisy camera. You will get banding from the noise quantisation before you get banding from the lack of bit depth.

Besides which IMHO the extra noise that using ProRes with the Ninja will add isn't going to help the situation along. You'll certainly get better recordings using a Ninja than the internal Mpeg 2 at 35Mb/s, in particular if you shoot interlace but don't expect to see a big difference in the raw footage because you won't. It's only if you do heavy grading that the differences will show up and then you will be noise limited, not bit depth limited. In my experience ProRes adds noise during the encode stage.

Re: EX1R - HDMI output 8bit or 10bit?
 

Hmmm,... well? I never thought of the EX1R as being a high noise camera. (Although I certainly know that sensor technology has come pretty far in the past 2 years)

I'll be running under tons of lighting in front of a green screen, prolly with negative gain. (It's a rock video)

Alister, do you really think that 10 recording is a waist with the EX1R under strong lighting conditions? (if the EX1R is truly "10 bit")

I think that recent developments in image processing is forcing us all to reevaluate what we call "high gain" these days. 9db on an EX1r is "high". That same 9db on an FS100 is nothing! (I'm shocked at how good 15db looks on that thing)

Everything is relative I guess.

Thanks Alister.

P.S. Generally speaking, do you give the Atomos Ninja your "thumbs up"?

Re: EX1R - HDMI output 8bit or 10bit?
 

Don't get me wrong. I don't think the EX1 at 0db is excessively noisy, it's just compared to many other cameras it is noisy. Taking Sony's own noise figures (If I remember correctly) the EX1 is 54db, the PDW-700/F800 and PMW-350 are 59db. 6db is a halving of the amount of noise, so these camera have almost half the noise of the EX's and you can clearly see it in the images, in particular if you grade heavily where the difference is night and day.

The issue with these cameras is that the noise is distributed evenly across the entire image. It's in the highlights as well as the low key areas and this makes grading problematic. Unless you like increasing the amount of data storage you need, there is little to be gained recording an EX using 10 bit over 8 bit. This has been discussed many, many times in the external recorders forums. The noise modulation is larger than the 8 bit sample size, so all that 10 bit does is waste data on more accurate noise reproduction.

For the moment I'm on the wall with the Ninja, in all the unit's I have played with so far the firmware has been too buggy for my liking. I've yet to see one play anything back correctly and if you can't review your material on location then how can you be sure everything is working correctly? Perhaps later firmware builds will resolve (or have resolved) this, it certainly shows promise, but it's not for me at the moment.

Re: EX1R - HDMI output 8bit or 10bit?
 

Anyway for whatever its worth I really want to know what the bit depth of HDMI port in ex1/ex3 cameras is so that
at least that Question could be put to rest Ninja or no Ninja.

Re: EX1R - HDMI output 8bit or 10bit?
 

Alister, this raises a good point based upon the findings in the BBC WHP034-ADD64_rev3_Sony_PMW500 report. The PMW500 has the same CCD's as the 700/800. Alan Roberts, the author measures a sn of 54db with "noise suppression" off and a sn of 59db with "noise suppression" on. Recently, B&H is now also quoting these two sn figures. Alan goes on to say, "The price to be paid for this reduction of noise levels is a little softening of the picture." and he concludes, "Noise performance is ambiguous."

I am considering the purchase of PMW500, but the BBC report muddies the water. I want a sharp picture, thus if 54db is a good as it can get, then I will stay with my EX3.

Re: EX1R - HDMI output 8bit or 10bit?
 

The PDW-700/PMW-500 is much quieter than the EX cameras, NR on or NR off. In most cases the image softening from the NR is barely noticeable. According to Alan Roberts the EX1's noise figure is actually 44db, so big difference if you go by Alan's numbers.

However not all noise is created equal. Some noise is a lot more objectionable/noticeable than other noise. It depends on how fine it is and how "busy" it is.

Re: EX1R - HDMI output 8bit or 10bit?
 

Yes, thanks for that qualifier Alister. Allan Roberts EX1/3 report does point out a sn of 44db and some insight to provide an answer to the original question of this thread:

"Clearly, the noise levels change well in accord
with the slope of the gamma curve, there being
about 10dB between black and white. This
indicates that the camera front end is the prime
source of noise, and that the adcs are probably 12-
or 14-bit. Since the slope of the gamma curve is
unity when the signal level is about 50%, it is also
clear that the noise level is only about -44dB rather
than the claimed -54dB in the specification."

Sony has previously gone on record to clearly state that the EX1/3 outputs are 10-bits. Alister has put some real world observations into the effectiveness of these 10-bits.

Re: EX1R - HDMI output 8bit or 10bit?
 

Considering this noise-floor talk all is indeed true, is there any advantage to running at negative gain?

Or, will that not change the inherent noise characteristics at all from 0db?

I would expect that if you ran at -3db, you could expect a 3db reduction in noise? Or....hmmm,...does that increase the overall signal to noise ratio by 3db? (or is that just wishful thinking?)

CT

Re: EX1R - HDMI output 8bit or 10bit?
 

Negative gain may have a positive benefit on noise (though it's doubtful whether it will substantially affect the 8-10 bit debate) but is quite likely to have an adverse effect on highlight performance.

In simplest terms, the max output from the sensor should be far more than necessary to give 100% exposure - the difference can be processed to retain detail in the highlights. Use negative gain, and a higher chip output is required for basic exposure, so less headroom available to retain detail in the highlights.

Re: EX1R - HDMI output 8bit or 10bit?
 

According to Dan Keaton from Convergent Design, all HDMI outputs on today's cameras are 8bit.

Some have posited that the HDMI outputs are only 8bit because all HDMI connections on TVs are only 8bit. So, these 8bit HDMI ports are mass produced and cheap whereas a 10bit HDMI port would be expensive and have low demand.

Re: EX1R - HDMI output 8bit or 10bit?
 

I think the notion that the HDMI output is only 8 bit due to the use of mass market 8 bit components is a valid one. When the EX1R was developed there weren't any external 10 bit HDMI recorders and 10 bit HDMI monitors were zero, so there would have been no foreseeable need to use more expensive or specially developed 10 bit devices.

I don't think many people realise that the vast majority of LCD TV panels are only 6 bit. They have a 8 bit input to give a reasonable overhead for processing and gamma correction before display on a 6 bit panel. 8 bit panels are appearing now, but are still not common, 10 bit even rarer. Many of the banding issues we see in our computer based edit suites or on TV are due to these 6 bit panels.

Negative gain reduces dynamic range as it will artificially clip your low key parts of the image. The brightness range is restricted by the cameras DSP, it only has so many bits to sample the sensors output, from dark to light. If you reduce the gain the highlight handling doesn't change (DSP bit depth limited) but your entire image get shifted down and as a result you will clip off some of your shadow and dark information, so your overall dynamic range is also reduced. 3db is half a stop (6db = 1 stop) so -3db gain reduces the dynamic range by half a stop.

Interestingly the PMW-F3 has an excess of dynamic range for the normal gammas and cinegammas and the processing appears to take advantage of this to keep the images very clean. When you shoot with the standard gammas and cinegammas on the F3 the cameras base ISO (sensitivity) is 400 asa at 25p. This gives a very clean, ultra low noise image with 11.5 stops of dynamic range. When you switch the camera to S-Log, which gives a greater dynamic range (approx 13 stops by my estimation) the base ISO increases to 800 asa. Looking at some of my S-Log test footage a clear increase in under exposure latitude can be seen when you use S-Log. I suspect that the "0db" point in the F3 is actually 800 asa as used by S-Log, where maximising dynamic range and using the full sensor range is the priority. Meanwhile with standard gammas, which are limited to 11.5 stops anyway, you can reduce the gain by 6db (1 stop) sacrificing one stop of underexposure but still have the full 11.5 stops but with 6db less noise.

Re: EX1R - HDMI output 8bit or 10bit?
 

Ok, this is a fantastic thread. Thank you to all for the info. I can honestly say that I understand about 81.5% of all that has been said here so far. (Alister can sometimes go over my head a bit though...I've got to read slowly and really pay close attention to keep up with him!)

So, here is my bottom line question;

If you were shooting a rock video in front of a green screen with tons of available light and your goal was to create a very sharp, clean and VERY bright looking video with deep, surreal and over saturated colors...would you shoot negative gain?

From what I'm understanding now, it won't seem to do me any noticeable good. (in the cleanliness of my video...and I'd be trading off some overall dynamic range for it)

I might buy an Atomos Ninja or just capture to a Blackmagic Design Intensity card. (4:2:2, 8 bit it seems)

CT

Re: EX1R - HDMI output 8bit or 10bit?
 

The best workflow I have found for grading is to take your recordings, process them with Neat Video (plug-in) and export with Cineform. Then, bring into your program to grade. (I use Premiere Pro CS5 with Neat Video and export to Cineform 422 Film Scan 1 and AE to grade). FYI, if you render to 444 with Cineform, you lose the super whites. I also use a nanoFlash for my high quality recordings (280Mb I-frame).

Re: EX1R - HDMI output 8bit or 10bit?
 

Haven't been shooting rock videos, but I do a lot of green screen and would HIGHLY recommend using an external recorder to give you 4:2:2 color recording.
I personally haven't noticed a big difference in the mattes coming off stuff shot at -3db compared to 0db, but in the last couple of months I've switched cameras and am now using an F3 into my NanoFlash for green screen work. Because I like to use a narrow shutter angle to minimize edge blur, I have been tending to shoot at 0db, and the results have been great.
The other issue in your post is the 'over-saturated colors' -- you may want to be careful because any kind of chroma bleed can be your enemy. If you can do your over-saturating AFTER pulling your key that might be a better approach.
But the bottom line is, I wouldn't consider shooting a green screen at anything less than 4:2:2.

Re: EX1R - HDMI output 8bit or 10bit?
 

If I don't pickup a Ninja than I will certainly be capturing to a Black Magic Intensity card using the MJPEG 8bit 4:2:2 codec. (eehh,...not sure about that codec yet)

Another issue with the HDMI out - My favorite frame rate is 29.97p. I love that look over 24p. (I feel that a progressive 29.97p will move nicely into a 60i for Blu Ray if needed...it still maintains the "progressive" look because the fields are sliced from the same frame)

I have a funny feeling that the the EX1r will process 29.97p right up until it gets to the HDMI port. I'll bet that it will break out those frames out into top/bottom fields to maintain TV compatibility. (like the Sony NEX VG10 does)

I plan to be careful with my levels and I'm going to shoot everything within range. My plan is to screw up and exaggerate the colors only afterwards, in post.

Thanks everybody. This has been a great topic.

CT

Re: EX1R - HDMI output 8bit or 10bit?
 

Perversely, if you want to shoot something that contains lots of highly saturated colors it can be beneficial to reduce the overall saturation level of the color matrix to prevent colors from clipping in camera and then bring them up again in post. If it gets clipped in camera you will get blocky colors in the finished video. There was a more in depth discussion about this with regard to shooting Hi-Vis jackets in another thread.

Re: EX1R - HDMI output 8bit or 10bit?
 

That's not my understanding - I agree with the last bit "so -3db gain reduces the dynamic range by half a stop", but surely it's at the expense of highlight handling, not lowlight?

The rationale is that the output of any photosite is physically limited to a maximum value, put more light on it, get a bigger signal out - subject to a maximum.

So assume the output value could increase from 0 to a nominal max value of 1000 (say) for increasing incident light, after that, no matter how much brighter it gets, you don't get a value of more than 1000. Now assume that an output peak white is nominally associated with a value (and light level) corresponding to 200 (say). All that headroom (from 200-1000) is available to allow for processing to give highlight detail instead of a hard clip.

The effect of negative gain is to mean that to correspond to peak white output, the output of the chip must be higher - say 400 for the previous example. So far less headroom (2.5x v 5x) to play with between nominal white and max chip output. Result - less highlight capability, but quieter in the blacks.

Re: EX1R - HDMI output 8bit or 10bit?
 

We agree, but are saying it slightly different pedantic ways. For those not interested in the science skip to the end paragraph as that's the only bit that really counts!

With most modern digital cameras it will be the low end thats clipped and the reduction in latitude is a reduction in underexposure range. The sensor itself is a constant gain device and with a CMOS sensor the A/D is done on the sensor chip. Once a certain maximum light threshold is reached the sensor will saturate and cannot output any more. So a fixed maximum dynamic range and bit range will leave the sensor and go into the DSP, the over exposure and under exposure limits of the system are determined by the sensor and it's bit depth or by the number of bits the DSP uses. The DSP will shift the gain up and down whilst applying the gamma curves etc. So if you reduce the gain, it is the bottom end of the available range that will be clipped, as it becomes sub-black. The high end just changes in output value with the signal level reducing for the same amount of light input. More light will not increase the output as the sensor will already be saturated.

Lets consider a scene where we adjust the iris so that the sensor's output is just starting to clip, so adding more light to the scene will not give any greater video output signal.

Imagine your sensor is outputting bit range of 0 to 1000 when the scene goes from black to maximum illumination at 0db, which in turn gives an output range of 0 to 100%. If you use negative gain in the DSP then bit 1000 gets reduced lets say to bit 900 and Black becomes -100 so now what used to exist between bits 0 and 100 can no longer be seen as these are below black (reduction in under exposure range) but nothing changes in the highlights other than a reduction in output level. The dynamic range is shifted down as input bits 100 to 1000 are now represented by output bits 0 to 900 and the output voltage range becomes 0 to 90%. The same illumination now gives only 90% output. This is clearly seen on an EX as the reduction in output level at -3db.

So with our fixed light range scene, the video cameras output will reduce by -3db and the picture will look darker. We will still see all the brighter parts of the scene as at 0db, just a little darker looking on the monitor. What we will not see is what used to be in the shadow areas.

If we do now increase the lighting, as the sensor is already max'd out, we won't see any further increase in the cameras peak output, but then at 0db this would have been in exactly the same situation. So the camera will still handle the same amount of bright light as before but we have lost some of the ability to see into the shadows.

So if you measure form a fixed reference point in the scene then you are loosing the ability to see into shadows relative to your highlights. However, measuring from Black to light it would appear that it is the highlights that have become more limited as the peak output level has been reduced, but actually the amount of bright light the camera can handle hasn't actually changed, it's just become less able to reproduce shadows.

Of course in practice it all means the same thing as you would compensate for the darker image by opening up the iris, which would bring the shadows back up again, but because the sensor is already saturated the peak output won't change.

Re: EX1R - HDMI output 8bit or 10bit?
 

No - gain is a multiplication/division process - not addition/subtraction. What you are describing is an overall level shift - not a gain change. It's also not true to think that max sensor output corresponds to nominal white, in practice it will be very much more.

In the absence of knee etc, if the sensor is starting to clip, it's outputting many times more level than would translate to peak white. Normal working is well below sensor limiting. Let's assume (in the absence of knee, and ignoring gamma) using your own figures that at 0dB peak output white corresponds to 200 as sensor value. If we now have -6dB gain, we need twice the sensor value to give the same output - 400 - which can be achieved by doubling the incident light level, exactly as expected. With all inbetween values also multiplied by 2 - not having a fixed value added.

Conversely, imagine if the light drops to only give a sensor output of 100 corresponding to white, 50 for mid grey (instead of 200 and 100). If we want that to correspond to the previous values, we need to MULTIPLY by 2 - not add 100. Which is the same as adding 6dB of gain.

In your example, it's the sensor values between 200 and 1000 (at 0dB) which normally get processed to give the knee. At -6dB there will be less headroom (400-1000) so the knee can't be as effective.

Re: EX1R - HDMI output 8bit or 10bit?
 

I still have to disagree with you David.

I'm well aware that gain is a multiplier. But the application of negative gain will shift a signal range down so my example is completely valid.

With an analog camera I might agree with you, but this is a digital camera. There is an old rule of thumb that says for every stop you want to record you need 1 bit of data, so for 8 stops you need 8 bits of data, 12 bits for 12 stops etc, while technically yes you can record 12 stops with just 1 bit of data (black =0, +12 stops =1) you really don't want to, and the 1 bit 1 stop rule normally holds true before you start applying gamma curves and other compression.

We know the EX1 and EX3 uses a 12 bit DSP, so it's not unreasonable to believe that the sensor is outputting a little under 12 stops of latitude allowing for correction bits etc. within 12 bits of data. This would be a pretty standard system and an efficient use of the available data pipe. Remember a sensor is a linear device, so to add another stop of dynamic range prior to the DSP requires a doubling of the amount of data and this is a budget camera so the designers are not going to use a larger bit depth (with all the associated extra costs) than is necessary to achieve the desired output. Nor do they want to waste valuable data bits with latitude that will never been used. So I hypothesise that in order to maximise the quality of the front end of the camera the designers would probably simply allow anything over 12 stops to clip as digitising anything over 12 stops is an absolute waste of valuable data as it will never see the light of day. So in effect the system is as I said already working within a limited Dynamic Range, probably around 11.5 stops absolute max at the sensor output.

We cannot ignore gamma and the knee, because as has been measured many times the EX1 has around 11 stops of Lattitude with the Cinegammas or a well adjusted knee.

So allowing for some noise reduction and other processing overheads, when you are using a cinegamma or the knee, which is on by default, the camera is likely to be outputting pretty much every bit of available sensor data. Even after subtracting 3db of gain, increasing light levels won't help as the A to D's and the digital pipe into the DSP is saturated due to the 12 bit nature of the pre gamma system.

This is born out in practice by the way the actual output signal from the EX cameras reduces by 3db when you use -3db gain and you cannot, even with more light get back up to full output. The only way to get back to full output is to adjust the gamma curve slope in the picture profiles which increases the gamma gain and allows you to increase the highlight gain. If you do this you can get your highlights back to where they were before you added -3db but still end up with clipped shadow areas. This tells me that the drop in output associated with the use of -3db is not simply a bug in the way the white clip is applied but simply because there is no more latitude to be had.

You can see the very behaviour I have explained with a waveform monitor. If you take an overexposed scene and look at it carefully on a WFM, then reduce the gain by 3db there is no change to the way the overexposure rolls off, it is exactly the same, the highlights are captured in exactly the same manner, just output at a reduced level, but you will see previously visible shadow detail simply disappear as there is now insufficient gain to show those subtle shadow textures, which is also of course why the noise is less visible. Lets not forget that noise is not that dissimilar to dark parts of the scene, normally small random changes in brightness and colour. If reducing the gain is helping us make the noise go away, it is also making subtle dark parts of the image go away, a reduction in underexposure latitude!

Further confirmation of this behaviour can be seen if you use a standard gamma and turn the knee off. Taking the gain down to -3db now does not result in an automatic decrease in peak white output by 3db because now our standard gamma non-knee image only has about a 7.5 stop range (funny that: 8 bits = roughly 8 stops, it's not a coincidence), so now we do have an excess 3 stop of latitude that are not getting used, again this confirms that when using the knee (which is on by default or a cinegamma) we are using the full latitude range available to us, there is no headroom that can be used by compensating with more light. So the sensor/data pipe is limited at approx 11.5 stops.

David, If we had a large excess of headroom as you suggest, then a well adjusted knee slope would give you a greater dynamic range, beyond 11 stops, but this is not the case, with the vast majority of cameras that use a 12 bit data pipe from the sensor to the DSP we hit a brick wall at around 11 to 11.5 stops, it's the point at which the data pipe becomes saturated. It's why as we have seen the number of bit's used in DSP's increase we have seen corresponding increases in dynamic range, it's more than just a coincidence.

So, if you are doing a shoot where dynamic range is an issue, the likelihood is that you would be using a cinegamma or knee to help deal with the wide dynamic range. Reducing the gain by 3db will reduce noise by a small amount but it will also make the darkest parts of your scene disappear. Increasing the lighting to compensate (or opening the iris) for the loss of those shadow areas will bring them back, what you are doing is decreasing your underexposure. However as your highlight range may well already be clipping you will not see any difference to your highlights other than increased clipping. It is very clearly the underexposure range that is reduced and this can be seen on a WFM.

This has been an interesting discussion as it has made me look much more closely at the way the output level of the EX and PMW cameras decreases when you use -3db gain. It's not just a quirk of the way the gain is applied but simply the case that there is no more headroom to be had when using the knee or cinegamma. Auto knee does disguise the effect a little, but a fixed knee or cinegamma clearly illustrates that the camera has an absolute limit of around 11.5 stops coming off the sensor.

Re: EX1R - HDMI output 8bit or 10bit?
 

Hmmm - OK, I think if there's any disagreement, it's because I've been talking in very general terms (very idealised and simplified theory) - you've been referring very specifically to how an EX behaves.

In my hypothetical camera, then the blacks should stay at the same level, and all the changes (esp knee slope) should happen at the white end. The settings (knee, gamma near black etc) should all adapt to compensate for the changing gain. When you say "the actual output signal from the EX cameras reduces by 3db when you use -3db gain and you cannot, even with more light get back up to full output. The only way to get back to full output is to adjust the gamma curve slope in the picture profiles ...... then it's obviously not adapting. (Which frankly I think it should be - you shouldn't have to adjust gamma curves manually when you change gain.....)

I also suspect that in the practical case of the EX, it really warrants readjustment of the black gamma with the addition of negative gain. I would still maintain that a camera shouldn't give clipped blacks with negative gain. If it is doing so, it's a sign that it's not automatically readjusting process values near black when the gain is changed - which I feel it should be doing.

Where I won't disagree is in all you say about overall dynamic range - and negative gain shouldn't change that in total. I would expect it to redistribute it (to the gain of the lowlights/expense of highlights), but it sounds as if to reach optimum, the camera needs manual realignment between 0 and -3dB.

You see, this is exactly what I meant when I said "it's the sensor values between 200 and 1000 (at 0dB) which normally get processed to give the knee. At -6dB there will be less headroom (400-1000) so the knee can't be as effective. I'd expect a camera to vary the knee processing when negative gain is used - not use the same multiplying factors as for 0dB. Yes, there is less headroom, highlight handling won't be as effective, but the white output level will be what is expected.

Love to talk it all over with you in person, Alister - far too open to misunderstanding to discuss complex issues in internet posts......!

Re: EX1R - HDMI output 8bit or 10bit?
 

I think your are missing the point that -3db is not just less gain but it is 3db of attenuation.

The majority of modern cameras exhibit exactly the same behaviour as the EX's, certainly most Pana HVX and HPX cameras do:

Dynamic range is the ability of the camera to handle the tonal range of a scene from shadow to bright light.

The amount of bright light the camera can deal with is limited by the point at which the sensor/data pipe saturates.

The signal output relative to light input is governed by the gain of the camera.

Reducing the gain reduces the relative output signal, but the peak amount of light the sensor and thus camera can cope with does not change. This is a constant, governed by the sensor, so highlight handling does not change.

Attenuating (-3d is an attenuation, not just less gain but negative gain) small signals may make them so small that they are no longer visible, Signals that are only 3db above zero become zero. That's why the noise level decreases.

Shadow areas of the scene are small signals. Attenuating these by 3db may make these no longer visible. Parts of the scene that previously were 3db above zero are no longer visible.

But the upper limit of what the sensor can handle does not change, only the relative output signal.

So: Attenuating the incoming signal from the sensor by 3db will prevent the bottom 3db of the sensors signal range from being seen while the upper range does not change, only the relative output level.

Using 3db of attenuation reduces the shadow performance of the system (small signals near black are lost, but bright light (and thus overexposure performance) does not change. So dynamic range reduces by 3db due to a loss of shadow information.

See attached graph, or see Art Adams explaination here: ProVideo Coalition.com: Stunning Good Looks by Art Adams

Re: EX1R - HDMI output 8bit or 10bit?
 

What a fantastic discussion. I hope more people notice this tread and take a look at it.

Alister, I dont think it's possible to explain this the technicals of situation and better than you just did. For a while, I often wondered why cameras didn't have deeper negative gains than they do. (if -3db would reduce noise than why not -6 or -9db? enabled. etc...) It's now clear to see why!

I will be shooting at 0db for sure. Bottom line for me is that I love dynamic range more than I hate noise and the trade off value doesn't seem worth it.

Thanks again to Alister and David.

CT

Re: EX1R - HDMI output 8bit or 10bit?
 

I'm afraid that Art Adams explanation is fundamentally flawed. With reference to his diagrams, he says:
The first sentence is completely true. The raw sensor output will depend on incident light, end of story. But the "window" (which represents the subsequent processing) analogy he gives is wrong. Simply moving it side to side in his analogy represents level shifting - not gain changing. Gain changing would correspond to making the window smaller or larger.

Think of it this way. Assume the raw sensor output can go from 0 (black), to 1000 (bright as it can be) - and these numbers are ONLY dependent on incident light. Now assume that for "0dB processing" they are translated into values 0 to 100 - so 0 output = black, 100 output = white. 10 input values map to 1 output value, OK? Now, the incident light level is halved - so the sensor values only go from 0 to 500. We would expect 6dB of gain to give us back a max output of 100 - the gain compensating for the halving of incident light - so in this case the 500 must be made to map to 1000. As far as processing is concerned, the impact of the 6dB gain increase is to mean that now 5 input values map to 1 output value, not 10:1.

In Art's "window" analogy, the window at 6dB is now only half the width it was at 0dB. The window has changed in size, NOT just moved, as he says.

In real life, gamma, knee etc make it far more difficult. but they only really represent a dynamically changing gain with light input level. Normally highest at low light levels, "nominal" in the middle of the curve, and low in the highlights. Practically, the variation is continuous, but let's assume it happens in three discreet parts for ease of explanation.

(Some readers may wish to stop here....... :-) )

Still using the 0-1000 model for raw sensor output, and 0-100 for output, let's assume that the lowlights are 0-10 in terms of output, mid range is 10-90, and highlights are 90-100. We'll assume that "normal" 0dB gain represents a 5:1 mapping in the mid tones, and 2:1 mapping (higher gain) in the lowlights. Hence, input values 0-20 map to 0-10, 21-420 map to 10-90, and 421-1000 map to 90-100 (about 60:1 - far lower gain).

Now let's assume we reduce the gain by -6dB (numbers are easier than -3dB!). The low end mapping becomes 4:1, mid-end 10:1. But IF we now map 0-40 to 0-10, and 41-840 to 11-90 AND open the iris a stop, the effect on the low and mid-tones (all the way up to 90IRE) is exactly the same. Dropping the gain does not necessarily mean a lack of shadow detail - in this case it will be exactly the same, and with lower noise due to the lower gain near black..

Of course, in that example there would be a terrible price to pay in the highlights. Opening the iris a stop would mean that many output values would be saturated compared to the first case (give a value of 1000) and highlight detail lost - but that's exactly the point. Negative gain can (OK, should) improve performance in the blacks - at the expense of highlights. You're robbing Peter to pay Paul.

That is obviously an extreme example, and in real life a lot of things will be different. But it begs the question of why the EX and Panasonic cameras mentioned by Alister and Art behave as they do. I suspect it's because the differential gain changing doesn't change with overall gain as it ideally should. In the above example, it corresponds to applying the high lowlight gain to sensor values 0-20 (as for 0dB) - rather than modifying it to 0-40. As such, it's right to see it as a bug, and not something that is inherent.

Re: EX1R - HDMI output 8bit or 10bit?
 

But you are ignoring the fact that 0db does not mean zero sensor output. 0db is likely to be some way up the sensors output range at the point where the engineers have decided that the signal to noise ratio represents the optimum compromise with regard to sensitivity and DR. Then you have to remember that -3d is not just a reduction in gain but an ATTENUATION of the input signal.

But that's exactly mine and Arts point. To compensate for the lower gain you have had to open the iris to regain your lost/reduced blacks and mids. The highlight handling of the sensor however has not changed, so now your highlights have become over exposed due to the need to open the iris a stop to regain the lost low end. Your having to deliberately over expose to compensate for lost low end, but because your over exposing your highlights are now blown out. If you didn't open up the iris the highlight handling would remain the same, so highlight performance has NOT changed, it's governed by the DSP's data pipe. And what happens to the input signal from the sensor that is now being ATTENUATED by 6db? Zero sensor output does not equal zero signal.

You muddling signal output levels with the actual dynamic range of the camera. Differing amounts of positive gain will of course vary the output signal level, possibly taking it above or below peak white, but this is an output level change, not a dynamic range change. ATTENUATING the input however will mean that some small signals will be lost and this results in a change in dynamic range.

I think my graph explains the behaviour of almost every current Sony and Pana camera. You have a limited optimum signal range dictated by the DSP, especially at the high end where every additional stop of over exposure requires a doubling of the amount of data used (remember a sensor and it's data output is linear). You cannot ever exceed that maximum data point, so the highlight handling remains fixed. The zero point will be somewhere above zero sensor output to allow for noise reduction and noise floor/sensitivity optimisation (and outputting underexposure requires a fraction of the data as over exposure). Attenuating the signal by 3db will reduce the maximum output level by 3db, but as this is well above zero this ends up as nothing more than an output signal level change (as seen in the 3db peak output drop). But attenuating a small signal that may only be 3db above the noise floor by 3db will mean that small signal is now zero and is lost.

If you attenuate the input signal going into an amplifier by 3db you won't see or hear signals until they are greater than +3db, so therefore they are lost, while signals greater than +3db will be heard or visible but now at a reduced level. So, low end is lost, high end the same but reduced level. -3d is an ATTENUATOR. not just less amplifier gain.