Hoping for book on HMC-150
- Thread starter rtmst3k
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Barry_Green
Moderator
Hizzo, I'm showing an order that was placed at 5:20 p.m. on Saturday; that was past the mail shipping cutoff so that package went out this morning. I'll PM you your delivery confirmation number.
Barry, thanks for the quick delivery but I must say something, I got it this morning and have gone through almost the whole book and honestly I bought the book hoping that there would be a lot of information on the "knee" function, no picture examples nor graphs were provided and that was something I was hoping for because I want to learn about the knee very much because I shoot mostly B press, I have asked a lot of questions regarding the knee and still to this day I do not know how to use it, Barry I understand that you cannot do anything about this as this is a personal issue, do you have any recommendations on where I can get much more information regarding the knee?
thanks
thanks
Barry_Green
Moderator
The knee is really simple -- it rolls off the highlights. It compresses the top end of the signal. The more aggressively you set it, the more it darkens your highlights. There are three settings, low/mid/high. Low starts compressing highlights when they reach 80% of the total brightness, mid ignores 80% and starts compressing when the highlights hit 90%, and high ignores everything until it hits 100%, and then starts compressing.
If you're familiar with an audio "limiter", the knee is vaguely similar to how an audio limiter works.
The pictures in there show how the knee reacts to the different levels of highly bright images; you can see that the highest brightness stays pretty much the same but the tones nearer to the top change based on what the knee is set at, the lower you have the knee the darker those two tones will be.
There are pictures on the CD that might explain it better; look in the "scene file explanation pictures" for the three pics "knee high chart", "knee mid chart", and "knee low chart". Those are shots of a DSC Labs' ToNi (toe/knee) chart, they were all shot at the exact same exposure and the only difference is the knee setting. You can easily see how the brighter tones get rendered slightly differently, and how the lower you go on the knee, the darker the bright tones will generally be.
There are also full-color scenes with the knee in each position, named "knee high", "knee mid", and "knee low".
I used the same explanation in the book as from the HPX+HVX Book, as everyone seemed happy with that, but for those that want to dig more into it be sure to look on the CD. There are strict limits as to what color printing can accurately represent, but the images on the disc are raw frame exports and will probably prove to be more illuminating.
If you're familiar with an audio "limiter", the knee is vaguely similar to how an audio limiter works.
The pictures in there show how the knee reacts to the different levels of highly bright images; you can see that the highest brightness stays pretty much the same but the tones nearer to the top change based on what the knee is set at, the lower you have the knee the darker those two tones will be.
There are pictures on the CD that might explain it better; look in the "scene file explanation pictures" for the three pics "knee high chart", "knee mid chart", and "knee low chart". Those are shots of a DSC Labs' ToNi (toe/knee) chart, they were all shot at the exact same exposure and the only difference is the knee setting. You can easily see how the brighter tones get rendered slightly differently, and how the lower you go on the knee, the darker the bright tones will generally be.
There are also full-color scenes with the knee in each position, named "knee high", "knee mid", and "knee low".
I used the same explanation in the book as from the HPX+HVX Book, as everyone seemed happy with that, but for those that want to dig more into it be sure to look on the CD. There are strict limits as to what color printing can accurately represent, but the images on the disc are raw frame exports and will probably prove to be more illuminating.
I remember that quote from your HVX Bootcamp -- "Auto means auto." I've always left it on high to avoid the flicker you described and that I think I've encountered.
Am I correct in reading the above quote to mean that a low setting on the knee compromises dynamic range?
(I have to drive to Leesburg to get the copy we purchased -- so I'll read it from cover to cover later this week -- and I'm sure I'll have all sorts of dumb questions!)
Thanks!
Barry_Green
Moderator
Well, like all things, "it depends". On a brightly lit sunny exterior, frankly, I'd probably go for "low". One of the dreaded giveaways that you shot on "video" is to have blown-out highlights, and the lower you set the knee, the more aggressively the camcorder will reign in the highlights. It can't stop your clips from overexposing, but it will reduce the amount of information that gets recorded as super-bright, and can add some additional depth to your picture.
For an internal normally-lit scene, if you're carefully controlling your lighting, then you'd probably want the knee back on high so that there's less artificial processing going on. You can adjust your lighting to control the highlights however you want.
And if you don't want to think about it, mid isn't a bad place to be.
For an internal normally-lit scene, if you're carefully controlling your lighting, then you'd probably want the knee back on high so that there's less artificial processing going on. You can adjust your lighting to control the highlights however you want.
And if you don't want to think about it, mid isn't a bad place to be.
Barry_Green
Moderator
Well, no, in fact putting it on "low" can make it look like you've actually got a bit more dynamic range. You won't, of course, but it FEELS like you might, because you can more easily discern the differences in the brightest tones.
The knee doesn't make the camera clip any sooner or any later; pure white will still be pure white no matter what you do. What it does is it affects the 90% white to 80% white levels.
Having the knee on "high" will give you the most mathematically correct distribution of the bright tones. However, that's not always what you want. Sometimes you want some exaggerated discrimination between those tones; an example might be a cloudy white sky, with the knee on high it might look like everything's just blowing out, but with the knee on low it might darken the sky itself enough to differentiate it from the clouds somewhat. It's like the exact inverse of B.Press, where B.Press artificially mushes the dark tones together, the lower knee stretches the brighter tones apart.
I don't mean to drag this out -- but -- am I reading this correctly to mean that a low setting on skin tones might exaggerate the appearance of shadows?
Barry_Green
Moderator
Here's a graphical representation of how the knee on the HMC150 performs. This is a composite of three pictures; I took the exact same picture using knee on high, mid, and low, and then combined them into this one composite picture.
See how all the medium and darks are identical regardless of the knee setting. That tells you that the knee has nothing to do with the darker tones, just like the master pedestal has nothing to do with the brighter tones. In fact, the knee is sort of like the inverse of the master pedestal. The master pedestal lets you raise up or crush down the dark tones, and the knee (to a much more limited degree) lets you manipulate the handling of the brightest tones.
Those pictures are on The HMC150 CD, included in the back of the book. I just combined them all into one here, but the original raw pictures are on the CD.
The pictures here weren't quite bright enough to cause full 109% clipping on the brightest chip, but you can see that overall the top tones are about the same, and for each lowering of the knee setting the rest of the brighter tones are rendered darker.
See how all the medium and darks are identical regardless of the knee setting. That tells you that the knee has nothing to do with the darker tones, just like the master pedestal has nothing to do with the brighter tones. In fact, the knee is sort of like the inverse of the master pedestal. The master pedestal lets you raise up or crush down the dark tones, and the knee (to a much more limited degree) lets you manipulate the handling of the brightest tones.
Those pictures are on The HMC150 CD, included in the back of the book. I just combined them all into one here, but the original raw pictures are on the CD.
The pictures here weren't quite bright enough to cause full 109% clipping on the brightest chip, but you can see that overall the top tones are about the same, and for each lowering of the knee setting the rest of the brighter tones are rendered darker.
Barry_Green
Moderator
Well, I don't know that it really has to be avoided; I usually prefer the look of knee low (but then again, I like a lot of contrast in my pictures, I like a low master pedestal and a lot of saturation, so this could be a case of "season to taste".)
The knee on high would yield the tones the way that the camera naturally sees the light, and would probably be technically the most "correct". But... I don't know that it makes for the most aesthetically pleasing images. And that is entirely subjective and a matter of taste.
No, because the knee doesn't affect the darker areas at all. Look at the above picture and you'll see that there's no effect at all on the darks or shadow regions. And if you look on the CD at the "knee low" and "knee mid" and "knee high" files, you'll see the standard scene file setting with a full 11-step gray chart, black to white. The bottom 8 shades (black to 70% gray) all are identical in all three settings, the only changes occur in the top 3.
For skin tones, you really shouldn't have any skin tones in the range where the knee works at, in normal circumstances. The knee kicks in at about 80% of brightness (on low) or 90% of brightness (on mid) or 100% of brightness (out of 109, on high). Skin tones are usually considered "proper exposure" at around 60% for a caucasian, and lower for darker-skinned subjects. Even the very brightest highlights on a very fair-skinned person should probably not exceed 80%, and the knee ignores all elements of the image below 80%, so... ideally, the knee setting should have no effect on skin tones.
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