Setting Exposure
I would like to here from others how you set your black and white levels?
What procces do you go through? How do you correct for skin color? Because Vegas has so many ways to do things im trying to find the best way to do all of the above and now im really confused again. When i look at my corrected footage Im starting to guess that i have things right but now im not to sure. In wish Vegas had a plugin that you could raise/lower blacks,mids,whites... I like the way FCP can do this with exposure. Cheers Simon |
A tutorial on using levels:
http://www.vasst.com/resource.aspx?i...0-90d2f8de9fc1 Vegas' color corrector and secondary color corrector is similar to FCP's. (Though a little different... in Vegas you have to "juggle" the controls if working in studio RGB). |
Thanks Glenn,
What about using color corrector and desaturate to get black & white image and then look at the image contrast and do levels from here? Simon |
There's a B&W plug. Insert that as the first link in the chain. Check it on when setting the luma curve, then check it off when returning to full color.
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Hi Jon,
I have been doing that for a while but have been using desaturate in the 3 wheel color FX with some succes. Cheers Simon |
Hi Glenn, we spoke before about the different settings in vegas in regards to studio rgb where you mentioned if i am working in native hdv and my output is mainly for tv/dvd, i should be in 32bit mode, 2.222 video gamma and uncheck studio rgb. Is this the same for the mxf format (PAL) coming from my sony ex1? Is studio rgb just for when your output is for computer viewing only? Thanks
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Daniel:
1- It's easier if you start your own thread for your question... this makes discussions easier to keep track of. 2- To answer your question, there used to be a clear logic as to which formats used studio RGB and which formats didn't. In 8-bit projects, video-world formats like DV, DVD, HDV, SDI, etc. use studio RGB levels. Computing-world formats like JPEGs, still images, etc. use computer RGB levels. In 32-bit the previous logic doesn't work... consult the table in my article. 2b- The EX1 probably behaves like other MPEG-2 footage in Vegas. So in 8-bit it's studio RGB, in 32-bit it's computer RGB. |
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Plus, the viewer will be looking at a color image anyways so you should be color correcting a color image in my opinion. |
Hi Glenn,
I'm think of getting Vegas+DVD, Vol. 4, Color Correction in Sony Vegas (DVD) Is this a Pal version? Cheers Simon |
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We've been using this order: * B&W (toggle on and off when setting levels) * Levels (for setting the luma color curve - usually some sort of S-curve. Look at the histogram to get the limits - 16-235 - right.) * HSL (for bringing the saturation in line with the luma curve) * Color correction for setting the right tone. One advantage that we've found is that by setting a nice S-curve, the color correction is less prone to contouring. We've been working in 8 bpc mode, rather than 32-float. |
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I'm not sure if this helps, but you can likely play a NTSC DVD on your computer without problems. (Sorry, I live in a NTSC country so I might be a little insensitive to those in PAL countries!) |
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As far as luma/chroma goes, only the color corrector filter can adjust one without affecting the other. The black & white filter and the HSL filter use different maths, so they affect both luma+chroma at once (not equally, but those filters affect both at once). |
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The main point is that after adjusting the s-curve with the levels control, the chroma saturation might be very, very wrong. If you don't look at the B&W image and/or ride the saturation control, a very nice luma curve could produce a horridly over/under saturated result. I've been guilty of this in the past - I make an ugly picture and back off, when the problem might be a secondary, rather than the primary, control. Regarding the math in the B&W vs. HSL adjustments (in 8bpc), they are different? Can you offer more detail? Y' = 0.587 G' + 0.299 R' + 0.114 B' in both cases, right? (The primes indicate gamma corrected domain.) Both the B&W and HSL saturation control should simply reduce the U and V channels, right? If I take U and V to zero with either filter, the result *should* be the same. If not, I'd love to know the specific difference. Thanks! |
The math for HSL is here:
http://en.wikipedia.org/wiki/HSL_and_HSV L = (MAX + MIN) / 2 MAX is whichever of red, green, and blue are the highest. Try this: Add the color bars generator. Stick on the HSL adjust filter. Set saturation to zero. You'll notice that all the bars have the same shade of grey. This doesn't happen with the Color corrector. You'll also see that the HSL affects luma values if you look at the waveform monitor (pick the "luminance" mode). Black&white filter takes the average. (R + G + B) / 3 |
Wow. Thanks Glenn. I'll check this out.
Having designed various hardware encoders, decoders, input and output modules in my career, I'm stunned when the standard YUV <=> RGB equations aren't used, and aren't noted in the UI. Y = (R+G+B)/3 is crazy talk! ;) ;) ;) This reinforces why we should always shoot color and then choose how we desaturate in post. That leaves us the most options. And you never know exactly what the camera might do with it's B&W equations. |
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Rec. 601 coefficients Rec. 709 coefficients (There are also coefficients that correspond to the SMPTE C primaries I think.) And if you want to do a better job, you can calculate luminance correctly. Use the 709 coefficients, apply the saturation adjustment on the gamma-corrected R'G'B' values. You need to do this in the gamma-corrected domain to get the hue looking right. You need to multiply the resulting values by some factor to get the correct luminance. You need to do those calculations in the linear light domain. |
Yeah, back in my hardware days (Grass Valley Emphasys Encoders & Decoders, Model 1000, Model 1200...) we only had to worry about 601.
It wasn't SD then. It was just video. :) Glenn, do you have a good link/reference for Rec. 709? |
ITU has a 3 free downloads promotion! (Yes, I get excited by stuff like that.) Take advantage of it, and download ITU-R BT. 709 for free.
Poynton's book and gamma FAQ and his website are also good resources. |
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