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My SL1 clips has excessive red channel? or is it a common problem?

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JonZ MarZ
My SL1 clips has excessive red channel? or is it a common problem?
on Apr 18, 2016 at 3:28:08 am
Last Edited By JonZ MarZ on Apr 18, 2016 at 3:36:45 am

I noticed that my Sl1 picks up a huge amount of red signal channel, way above 100 IRE in my video editor. That happen a lot when for example I film red cars, or people with red shirts. I think the yellows too but in much lower scale.

Is it something common to Canon, or a setting that cause that like a poor auto white balance? I pretty much have default settings but I played a lot with them.

Is there works around for this in for example Premiere Pro? or in the camera itself for future captures.

for example (quick find, not the most exaggerated red signal I found)
https://i.imgur.com/P2xePAw.jpg


Thanks.


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Blaise Douros
Re: My SL1 clips has excessive red channel? or is it a common problem?
on Apr 18, 2016 at 9:51:17 pm
Last Edited By Blaise Douros on Apr 18, 2016 at 9:55:59 pm

This is not a problem. The histograms and scopes that you're showing are correct for an extremely saturated subject in bright sunlight. You could underexpose the scene a bit if you're worried about the red channel clipping, but white balancing won't really solve much, given that you're working with low-bitrate AVCHD. You'd just create an off-balance image which you'd correct in post, probably introducing artifacts from grading a low-bitrate image.

The only way I can think of to keep this from clipping the reds would be to reduce the in-camera saturation control, for a flatter image. Again, though, AVCHD won't stand up to much grading. If your color is pretty accurate in-camera, and you don't plan to aggressively grade it in post, I don't see a problem with the image or the histogram.


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JonZ MarZ
Re: My SL1 clips has excessive red channel? or is it a common problem?
on Apr 19, 2016 at 4:47:17 am

ok Thanks for the clarification!

Maybe I can then fix this in post. Only, I can only desaturate 3 channels at once, I haven't found a tool that can desaturate only a channel if such thing exist in Premiere.


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Blaise Douros
Re: My SL1 clips has excessive red channel? or is it a common problem?
on Apr 19, 2016 at 4:51:56 pm

You may also be misreading your scopes, or don't understand the significance of what you're seeing. I see absolutely no problem with the image or with the scopes.

As I look at the Chroma scope, which is the circular one in the upper right, the red levels top out right at the broadcast safe mark. Totally acceptable.

Then, I look at the histogram below that in the lower right. This is not read the same way as the luma scope in the upper left; this is like a photo histogram, flipped on its side. It's showing that you have a lot of reds in the highlights, but none of it is clipping. Since there are lots of bright, saturated reds in the car, I would expect to see that.

Then I look at the luma scopes on the left side, as well as the individual color channels. Notice that the IRE scale is different on the channel scope versus the luma scope. The red channel shows a higher level of red than the other channels, but it's not clipping. Same with the luma scope--I don't see anything that suggests there's a problem with the image.

Which leads me to my final conclusion, which is that you don't understand how to read a scope. You have an extremely bright red object (and orange cones) that is prominent in the frame, the rest of which is grey pavement. This means that your red channel will show much higher levels than the other channels, because there is more red in the image than any other color.

Your scopes should NEVER show a perfectly balanced amount of color unless you're shooting a color chart. If you were shooting a scene in the forest, with a bunch of green leaves filling the scene, your green channel would show a spike, and this would be absolutely correct.

Your scopes are useful to look at when you know there's a problem with the color, and when you need to see exactly what changes you need to make in color grading to get one image to match another, for example. But don't make the mistake of believing that every image should show a perfectly balanced set of scopes, because any colorful scene will naturally have a unique mixture of colors that will produce a different reading on your scopes.


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JonZ MarZ
Re: My SL1 clips has excessive red channel? or is it a common problem?
on Apr 19, 2016 at 5:04:47 pm

I admit that I'm still unfamiliar to scopes, I use them mostly for white balance. Since the new Adobe CC redesign of the scopes, I'm still struggling to fully understand them. And a bit of the concerns also came from colleagues feedback saying that my reds are too bright on his HDTV, so it increase my confusions because like you said, the graphs seems to show nothing wrong overall.


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Blaise Douros
Re: My SL1 clips has excessive red channel? or is it a common problem?
on Apr 19, 2016 at 5:16:14 pm

So, given that the histogram looks correct, you could do one of two things: 1) take your friend's advice at face value and apply desaturation to the image (not just to the reds, because that would throw off the white balance) to dial back the colors a bit. Or, 2) check with your friend to see if his HDTV is properly calibrated. I suspect that the second option is probably more likely to solve the problem!

It's super important that you take the time to learn about how to read the waveform and vector scopes before you use them to inform any color correction decisions you make. And notice I say "inform;" the color scopes are a helpful tool, but your eye is far more important. An object that reads identically on the scopes in two different scenes can appear totally different to the eye, so you often have to cheat the color balance a little to make it look visually right.

Larry Jordan has a pretty good overview of using scopes--I recommend taking some time to dig into it.


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JonZ MarZ
Re: My SL1 clips has excessive red channel? or is it a common problem?
on Apr 19, 2016 at 7:20:01 pm
Last Edited By JonZ MarZ on Apr 19, 2016 at 7:25:31 pm

I happen to have watched some Larry Jordan educative videos recently :) But one thing from what he has told in one of his webinar, is if the chroma level is exceeding the vectorscope limit (from the boxes), then it is then oversaturated. Maybe I understood him wrong, or maybe it implying to be a rule that can be broken, or simply taking him out of context.

See it there






at 11:10 approx.

I see my red in the screenshot I provided to go over the line he kinda mentioned, and from there I had suppositions it could have been oversaturated
.
He is using FCPX thought, maybe the limits are different in Premiere.


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Blaise Douros
Re: My SL1 clips has excessive red channel? or is it a common problem?
on Apr 20, 2016 at 12:35:42 am

Your reds are going very slightly past the edge of the 75% usual broadcast safe mark. NTSC has about a 20% safety margin built in, which is what the outer marking is. You could bring saturation back a little to keep it safe. However, I do also recommend looking at your output file on a couple of different monitors to be sure.


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John Mayer
Re: My SL1 clips has excessive red channel? or is it a common problem?
on Apr 20, 2016 at 1:58:31 am
Last Edited By John Mayer on Apr 20, 2016 at 3:32:11 am

Ah yes. I think you are right, I've read this somewhere that the external boxes after the line are indeed the NTSC safes. And if I look closer to the FCPX vectorscope, the boxes distance matches the one in in Premiere Pro on the exterior.

Thanks for the insight! this will definitely help me on my judgements on my future editings.


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