GH4 "Log Jam ... a bit more than you ever wanted to know about shooting log"

Bern Caughey said:
Log Jam ... a bit more than you ever wanted to know about shooting log
by Ben Turley
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Thanks for another great read (I understood perhaps 40%). One of the biggest takeaway for me was this:

"If not handled well, log can lead to many headaches and, by its very flexible nature, the final image can easily end up utterlydisconnected from your artistic intentionbut with your name still on the credits."

So rather than clamoring for Panasonic to warn people about the limitations of 8-bit encoding, the above might have saved some people heartache, along with the understanding that shooting in log is not always preferable.

Despite my limited experience, I'm none the less very excited by the potential offered here.
 
stoneinapond said:
...So rather than clamoring for Panasonic to warn people about the limitations of 8-bit encoding, the above might have saved some people heartache, along with the understanding that shooting in log is not always preferable.
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But what this article also proved is that Log implementation between vendors can really help and hurt your shooting. Each and every time someone is complaining about V-Log, is not due to the distribution of the bits, but the lack of the bits used in an already information starved format. If Sony can Canon and do wonders using 256 bits to record their image, nevertheless the different resulting post exposure latitudes, then V-Log could have used 256 (instead of 160) and implemented in a way to give us one or the other, or maybe a hybrid of the two.
 
From the linked article:

...a difference of one between two colours in an 8-bit image will be invisible... Figure 4 is an 8-bit image featuring two different shades of gray one value apart. If you can spot the hidden message then very, very, very well done

fig4.png
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While true in this case, there's a sleight of hand to this claim that lies at the core of the chroma smearing artifacts seen in 8-bit V-Log-L recordings. Notice that the author is refering to "shades of gray", which means the values are one step apart in the luma channel of the YUV encoding. The problem with 8-bit V-Log-L becomes visible when you have almost-gray tinted hues one step apart in the chroma channels, which the H.264 codec encodes much more coarsely than the luma channel. This can produce blotchy magenta/green artifacts that are clearly distinguishable to our eyes.
 
Really great read.

I'm fortunate enough that a great deal of the shows I work on, I'm able to have control over both the shooting and coloring processes. For this reason, I always tend to shoot Log when possible. But I've shot stuff in the past where the "colorist," barely even touched the footage and the end result was an incredibly ugly, dull looking film.
 
Lpowell said:
From the linked article:

...a difference of one between two colours in an 8-bit image will be invisible... Figure 4 is an 8-bit image featuring two different shades of gray one value apart. If you can spot the hidden message then very, very, very well done
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but mmm i can see the text in there...i dont think it's a very hard thing to see on a calibrated monitor.
 
mcnys said:
but mmm i can see the text in there...i dont think it's a very hard thing to see on a calibrated monitor.
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I would think the opposite to be true.

Think about it. If your monitor is capable of 10 bit precision in displaying colour, then a single value change, even with this 8 bit image, should be almost imperceptible (I could BARELY make it out on my high end calibrated monitor by really squinting hard).

If your monitor is an 8 bit or 6 bit panel, then it's going to interpolate the values with less precision, thereby making it easier to see the differences.

So I would be happier if I couldn't see it at all, as it would mean my monitor has more precision than needed to display the image, resulting in smooth tonal transitions and a lack of banding.

Maybe a better test would be this:

http://www.drycreekphoto.com/Learn/Calibration/monitor_gradient.htm

Cheers,

Paul :)
 
visceralpsyche said:
I would think the opposite to be true.

Think about it. If your monitor is capable of 10 bit precision in displaying colour, then a single value change, even with this 8 bit image, should be almost imperceptible (I could BARELY make it out on my high end calibrated monitor by really squinting hard).

If your monitor is an 8 bit or 6 bit panel, then it's going to interpolate the values with less precision, thereby making it easier to see the differences.

So I would be happier if I couldn't see it at all, as it would mean my monitor has more precision than needed to display the image, resulting in smooth tonal transitions and a lack of banding.

Maybe a better test would be this:

http://www.drycreekphoto.com/Learn/Calibration/monitor_gradient.htm

Cheers,

Paul :)
Click to expand...

ahhhh i get it now, my calibrated monitor is a 8 bit one, and monitor at work, i don't know....but i think its 6bit as you said, because, here at work i see the text actually better.

Thanks for clearing that out!
 
Here's a frame grab showing the difference in recording a log profile in 1080p at 50Mbps 8-bit H.264 at 4:2:0 color depth versus 4:2:2. It was shot on a JVC LS300 in J-Log1 profile at IS0 1600. Both versions were graded simply by lowering the Master Pedestal by -0.10 in Color Finesse via Adobe After Effects. In order to highlight the 420 vs 422 details, I boosted gamma to 200% and magnified the frame to 200% as well. The 420 version is on top, the 422 version below it.

LS300%20420%20vs%20422_1.jpg
 
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Hi All,

I wrote the article and I just have to say, you got me on that gray rectangle. When I first did it I'm shure I couldn't see the difference, but then I managed to delete the copy linked on my site around the time of publication. Uploading it again, I've got a feeling I've wound up making a copy with more than one 8-bit value's difference, 'caus it looks pretty obvious to me too now! :-)

Ah well, the point is 10-bit good, 8-bit tread carefully!

Ben
 
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