Solved Colours of camcorder not as expected

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Replied by Eagle Six on topic Colours of camcorder not as expected

Thank You for the update Patek,

I agree with your conclusion and it appears you are coming to grips with your situation.

My primary camera is a very old Canon XLH1, a very dated HDV. I have added a Atomos Samurai Blade digital recorder which adds some extended life, but even with that it doesn't have any of the latest bells and whistles like 4K, slow motion, or low light capability, or large CCD's. It does however offer advantages of determining precise exposure, determined by the operator of course, so if I do my part, it works rather well. In my opinion, I've never had a camera that takes perfect exposures, but most can come closer than I can, without leaning on exposure tools!!

Like yourself, I don't prefer overexposures. Being an old film photographer, I found it easier to bring up an underexposure, rather than down an overexposure. In a one or two stop underexposure, the definition is still there, but when the highlights are blowout by overexposure they are gone forever. I found this to also be true in digital video, so if I err on exposure I lean towards the underexposure side, within reason of course.

Hopefully with using your camera AE shift or manual exposure, you can achieve a better exposure in your videos. It takes time to figure out the override exposure settings based on the tools your camera provide, but it should be doable.

Good luck with it, I can appreciate your frustration and patience. What you have learned during this process and have updated here, may certainly help others.
Best Regards......George
01 Jun 2016 03:43 #11

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Replied by Patek on topic Colours of camcorder not as expected

Thanks, George, for your encouragement, and sorry for the delay in replying.

What I am currently doing with the exposure of my camcorder is:
I mainly rely on the preview monitor/viewfinder.

This may not sound intuitive because these monitors are not calibrated.

Still, overexposure can be detected as follows:
First, when I increase the exposure the image gets brighter.
(The Sony has some internal rules to increase exposure time and open the iris in some combination.
It is not possible to control both manually at the same time.)
When one channel starts to clip then suddenly the colour changes.
The relation between red, green and blue changes due to clipping in one channel.
It took for me some practice to see the difference between brightness changes and colour changes.

Here is an example.
Say, the recorded pixel has the value (200,200,50) rgb, which is yellowish.
Increasing exposure eventually leads to (255,255,120) just before clipping. [The 120 is probably not correct, the exact value depends on gamma.]
This is the same colour, just brighter.
Increasing the exposure further gives (255,255,170) which is a different coulour than (255,255,170), it is not only brighter.
Eventually, increased exposure gives white (255,255,255).

That is my workaround for the moment until I find a better solution.
Thanks so far for your feedback!
The following user(s) said Thank You: mmcswnavy24, Eagle Six
22 Jun 2016 08:04 #12

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Replied by Eagle Six on topic Colours of camcorder not as expected

Hi Patek,

Thank You for the reply feedback and the example of your workflow. I could pretty much tell from your opening post you are a craftsman. You go beyond the 'camera operator' point of becoming familiar with his equipment. You find the advantages and the weaknesses and as an artist you exploit both. I think this thread has become a lesson as how one can go way beyond the device design and make it fulfill your needs. It's not easy, it takes patience and perseverance and deep study of the elements to get the absolute best out of a camera and I think you are on that edge. I look forward to any additional updates you may post.
Best Regards......George
22 Jun 2016 08:43 #13

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Replied by Patek on topic Colours of camcorder not as expected

Thanks a lot, that is a very kind feedback :)
This certainly motivates me to spend more time on filming and to learn and share it here.

Still, I am only beginning to make first steps with video. This is visible e.g. in my last posting where I made
a small mistake: When the colour (200,200,50) in sRGB gets brighter then all components increase linearly,
so that clipping will occur at (255,255,64). That components in sRGB increase linearly when the colour
gets brighter is due to the gamma function being a power function.If it was another function, the relation
would be more complex.

Over the next time I will post a short observations on the gamma transfer function used e.g. in rec 709 and sRGB.
There is a lot of material on the internet about gamma functions, still there is one aspect I did not find and so had to work it out myself.
Another short post will be about the 16-235 range for video. There is a very good colour tutorial here at movie studio zen with
the explanation of the correct setting in the Vegas rendering. Still, maybe I can add an interesting observation for this topic.

Have a good start into the week!
The following user(s) said Thank You: Eagle Six
27 Jun 2016 07:53 #14

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