Mike Most
Forum Replies Created
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Hi Michael,
That’s what I thought might be the case. Actually, I generated the DNx files using Resolve, using the embedded header info for the tape name, but it yields the same result (a tape name without the _001 extension).
Surprised and pleased to hear about you going to New Orleans. Please say hi to Vinny and Bradley for me.
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No, if you do the math, it is approximately 2.5:1. Uncompressed HD is approx. 1.2 gigabits per second. The 440Mb rate is essentially identical to HDCam SR, and identical to the SR Master format Sony is offering with the F65.
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The Arri LUT generator allows you to either include a color matrix or not, it’s a user choice. This allows you to builld a LUT that can be used with Redlogfilm footage, for instnce. The Log C curve, while not completely identical to cineon, is close enough to use for almost all images coded to the Cineon standard. The reason I and others point users to the Arri site is because its the easiest and quickest way we know of to get a LUT in almost any required format, with or without the Arri color matrix, and in either direction (I.e., log to Lin or Lin to log). It’s a great resource whether you happen to be dealing with Alexa footage or not.
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Go to the Arri Digital website, navigate to the online LUT builder, and make one. Select Video as the source and LogC as the destination. Make sure you use extended range.
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>Question…must the folder inside the MXF folder always be a number ?
>And if it’s only numbers, can it be double or triple number like 10 or 100 ?Yes, and yes.
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If you need more speed, and you’re only doing dailies, and you’re only using one or two nodes, I would strongly suggest getting a second machine rather than one very fast one, splitting up the work using either multiple source drives or shared storage, and “ping ponging” which machine is being used as a workstation and which a renderer. The incremental increase in speed from a faster CPU won’t be particularly dramatic if you’re using a single machine approach. The way to do things faster is to be prepping and grading at the same time you’re rendering. The only way to do that is with more than one CPU. In the Mac world, the base Mac Pro costs about half as much as the fastest Mac Pro, but using two machines and splitting the work will be much faster in terms of total turnaround. You could even use iMacs for this and do it almost as efficiently. Or maybe even 3 or 4 Mac Minis.
Just a thought.
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>I just would like to add that moving the gain trackball along the correct axis effectively does the same >thing as Mike describes above.
No, it really doesn’t. Not only does the gain control have a range limitation (it has its pivot at 0, but the control range is not linear), it only controls the upper level limit of each of the three channels. What I was describing is a situation where the original image has its colors misbalanced across the luminance range, not just in the upper regions. In that situation, some of the information that should have been in the red channel in the first place has been improperly assigned to the blue channel. So by subtracting some of that information in the blue channel and reassigning it to the red channel – where it actually belongs – you’re accomplishing something a gain control cannot do, which is taking the information across all luminance levels from one channel and placing it in another. The result may appear similar in come cases, but in the case I was describing, a gain change would not solve the underlying problem.
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I specifically avoided using the words “warm” and “cool” because it seems to confuse people, as your post indicates. I did refer directly to color temperature, which is a number, measured in degrees Kelvin. A higher number is closer to daylight, which is very blue. A lower number is the opposite of that, or orange. So if you want to make a blue image less blue, you’d be lowering the color temperature, and vice versa. This requires a move along the red/blue axis. A tint control usually works along the opposing axis (opposing by 90 degrees), which would be the green/magenta axis. Since magenta is not a primary color, you control the tint by changing the green component of the green channel. The default in a typical matrix is to have the red channel consist of 100% red and no green or blue, the green channel 100% green with no red or blue, and the blue channel 100% blue with no red or green. So to move the information along an axis, you subtract the main component of one and add it to the other. That’s why I subtracted blue from blue (the one I wanted to move) and added it to red (where I wanted it to move to).
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>ps:what do you mean by “wrong Lut “? couldn’t you re-apply lut ?
I could if I was working from the original material. However, that is not the case. The show in question transcodes everything to DNx115 and hands us a mixdown, there is no conform. I don’t necessarily think this is a good way to post a show, but numerous shows are doing it anyway, so you have to make do with what you get.
>sometimes on alexa when i have the Log C image looks worm and nice , but applying a LogCtoVideo >+709 matrix (the WB gets weird (blue/green) ,
A LogC image is not meant to be looked at or judged for color. It is a data container. It is not a sensible image until is is “normalized” and has a color matrix applied, which is what the LUT does. I would refer you to my blog (mikemost.com) for more information (or opinion, call it what you will…) on that subject.
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You can use the Color Mixer, which is essentially a color matrix. A color temperature control basically alters the image along the red/cyan axis, and a tint control along the green/magenta axis. So to change the color temperature, you can change the blue component of the blue channel and the blue component of the red channel. In other words, to “lower” the temperature, lower the blue in the blue channel and raise it in the red channel. To “raise” the temperature, do the opposite. To change the tint, change the amount of green in the green channel.
The color mixer can be an extremely useful tool for things like this. In a show I currently work on, we had a number of scenes that were shot on Alexa but had an incorrect lut applied that shifted the color temperature and made the image very blue. By using the above technique, I was able to “normalize” the scene even though there was no “raw” image available.