Cine gamma settings in the EX1

[Max Allen]

Very interesting work. For what it's worth, if you're going for accuracy I would think an offset of 400k from 32k is starting to push it a bit, assuming you're correct about the native 32k design. I'm sure you know temperature change is detectable at 200k intervals to the eye, becoming very obvious as when reach 500k. If you can't hit 32k +/-100k personally I would draw the line at 2900k for your test. I also think it'd be interesting to see how great the effect of this variance is on the results.

[Serena Steuart]

Fair enough comment, Max. In this instance I was more interested in observing any change and had not expected the extent of it. Now it might be worth redoing for 3200K.

I'll recheck anyway, because that apparent difference makes me a little uneasy that there may be an error in data reduction (compensating for the change in source luminance).

[Bill Ravens]

whoa....this whole test has set me kind of on end. I just never considered the gamma change when resetting white balance. I shoot exclusively at 5800K. If I want to dial out too much yellow, I do it in post. So, as long as the gammas I'm studying are good for 5800K, I should be OK.

[Serena Steuart]

Originally Posted by Bill Ravens

whoa....this whole test has set me kind of on end. I just never considered the gamma change when resetting white balance.

Bill, it may be that I'll be embarrassed by being too quick in publishing that result. Have to find some time to check, so make no changes to your approach in the meantime!

[Gavin Rawlings]

Just for the ones that are having a hard time understanding these charts (probably only me on this entire forum) your units ascending on the left are IRE levels right? The subject brightness levels in 0.5 increments is what is confusing me the most though. If someone could just help me understand how that bottom line works that would be most appreciated.

Sorry for the dumb question in a technical thread guys...

[Serena Steuart]

There are no dumb questions! Sometimes dumb answers!
The vertical axis is IRE, although I understand that term as really belonging in the analogue world. So 100 is broadcast max and generally our digital cameras capture up to 109 before clipping. The horizontal axis is subject brightness relative to a chosen test set up. As the subject waxes or wanes (in brightness) so you move along the horizontal axis, each halving or doubling representing 1 stop change in brightness. The test point brightness was chosen to get 109 using cine gamma curve 4. You'll see that the standard gamma curves (1,2,3,4) reach 109 at much lower than that subject brightness.

Measuring the data is easy if a little tedious. In reducing the data allowances have to be made for changes in the test source, such as adding gels to adjust colour. I suspect my plot of the effects of WB show that I adjusted in the wrong direction, so greatly exaggerating any effects. I'll let you know! In the meantime, don't worry about the WB effects plot.

[Gavin Rawlings]

Originally Posted by Serena Steuart

The horizontal axis is subject brightness relative to a chosen test set up. As the subject waxes or wanes (in brightness) so you move along the horizontal axis, each halving or doubling representing 1 stop change in brightness. The test point brightness was chosen to get 109 using cine gamma curve 4.

Ahhh I get it now! Thanks for explaining Serena

[Serena Steuart]

Originally Posted by Serena Steuart

I've looked at the effect of changing WB and the results are attached.
I used the same subject source and added a full orange gel, which cut the source by a stop. The camera white balanced at 2800K, so I accepted that.
The effects are greater than I expected. The camera showed greater sensitivity and the results are plotted to retain relative subject brightness of 1.0 matching the previous plots. STND 1 gamma exhibits a steeper roll off (or knee) prior to clipping.

Unfortunately, for me, these interesting conclusions are wrong. I did indeed muck up reducing the results of that test, compensating in the wrong direction for the effects of the added gel. I redid the measurements for 3200K and differences in the curves between daylight and tungsten are small (measurement error band). Apologies for the trip up the garden path.

[Bill Ravens]

whew...

thanx for setting things straight. It was a mind boggler, for sure.

[Mervin Langley]

I have been shooting weddings with C1 (Bill's settings), detail off and have had good results. Yesterday I used C4 instead (all other settings unchanged). I found the image substantially "softer". Is there any reason that this may occur?

I calibrated my lens after the last firmware upgrade but that was 4 weddings ago. Is it possible that the calibration needs to be repeated?

Thanks,
Mervin

[Simon Denny]

I shot some footage going the other way Mervin by going from Cine 4 to Cine 3 and found Cine 3 to be softer. Oh I forgot that I shoot 720/50p with Cine 4 but on this shoot I shot Cine 3 1080/50i.
I have found that Cine 1 combined with Cine 3 yeilds the best combo in my opinion.

[Max Allen]

Originally Posted by Mervin Langley

I calibrated my lens after the last firmware upgrade but that was 4 weddings ago. Is it possible that the calibration needs to be repeated?

Thanks,
Mervin

Hi Mervin,

When you say calibrated your lens I guess you're talking back focus. I can't say this is the cause for softness but for interchangeable lens cameras the best routine is to calibrate that not only when a lens is mounted but also after the camera is moved/transported or there is an environmental temperature shift of a few degrees. Not always practical but recommended. If you have an EX1 perhaps this rule can be relaxed (fixed lens) but I would check it before every shoot really as preflight.

[Mark David Williams]

Originally Posted by Serena Steuart

Here is a plot of the four cine gammas plus standard 1 gamma. Given in two forms: the usual log of subject brightness, plus with a linear subject brightness which is the form in Sony's sketches.
The data was taken with the following conditions:
subject surface brightness: 16000 lux; 5600K; white; broad; diffuse.
Effective subject brightness at 1.0 on curves 900 lux approx.
WB: 5600K
camera gain: 0dB
shutter speed:1/50
HQ mode, 25fps
PP properties: default with knee "off" and changing only the gamma selected.
When iris was closed the brightness reading was 3%. This could have been adjusted using black level, but I left defaults as is.

The LCD shows image % brightness to a whole number, so accuracy decreases with decreasing reading. The readings are repeatable within 1 digit (generally get the same reading).

Serena Thank you so much for sharing this! ;) and everyones inciteful help.

[Dominik Krol]

I don't know how you guys derived at the "conclusion" that Cine gamma 1 is for bright/outdoor scenes, and Cine gamma 3/4 are for dark/indoor.

My tests have shown the following.

If you expose for skin tones at 70-75% in Cine 1, you will overexpose the white background/bright sky much faster, than you would in Cine 3 and 4.

If you set zebra 1 to 75 and enable zebra 2 which is at 100, you will expose the color chart "Caucasian" square at the same time. So 75% skin = 100% white at same exposure in Cine 1

Set the gamma to Cine 3, the white square will be sitting at 97% with the skin square is at 75%

Go down to Cine 4, and the white square will sit comfortable at 95%

This all means that you will have a better chance of maintaining your bright background and deep blue sky in Cine gamma 3 and 4.

I would also argue that the same logic can be applied when the situation is turned around.
In Cine 1 you will have more exposure in the poor lit shadows when shooting indoor, while Cine 3 and 4 will be more prone to crush the blacks.
The only reason for using Cine 3 and 4 indoor must be that the curve allows for less light and therefore less gain.

This all depends on what your subject is and therefore where your main exposure lies. But in most situations we are aiming the camera at a person.
75% exposure being your target, you want to make sure that the next most important thing, either the sky or the dark room is as close as possible.

Finally you can use Cine 2 for scenes which could introduce banding in the 8bit colorspace. Since Cine gamma 2 compresses the image to 100% white clipping (which btw can be changed back to 109 if you set the gamma level to -5), You will effectively have a better "dynamic range resolution" pr stop.

Same goes for all of you who use -3 DB gain.. If you set any of the Cine Gammas to -4 (cine gamma 2 to -9) You can maintain the dynamic range at 109%

[Alister Chapman]

Cinegammas are designed to be graded. They are not designed to be used in the same way as you would with a standard gamma and you need to adjust where you put your skin tones accordingly. Whenever you take a large range of something (in this case brightness range) and squeeze it into a narrower range (by displaying it on a TV or Monitor with a standard gamma) you are compressing the image.

Cinegammas will look flat when exposed correctly on a standard TV or monitor because the monitors gamma curve does not have the range to correctly display what the cinegamma has captured.

To restore your cinegamma footage to something that look best on a standard TV you need to grade it. Given that the main aim of the CG's is to capture more highlight information, and some of the mid-hi range is used for this extra highlight data, then you need to be prepared to move your CG midtones and skin tones upwards to traditional levels in post.

If you shoot using a CG and you have your skin tones at the traditional 70 ire (which is rubbish anyway as everyones face is different) then those skin tones are in the compressed part of the gamma curve and no amount of grading will ever make them look as good as they should. You must keep skin tones and natural textures at a lower level when using the CG's to avoid this compression. When using CG's you need to modify the way you expose to get the most out of them.