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Author Topic: Strange blue in place of black  (Read 2227 times)

Stewbyyy

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Strange blue in place of black
« on: July 13, 2013, 11:19:22 PM »
Hi guys,

I'm very new to video, I'm moving over slightly from a stills background as I've received funding to direct my first short film (of a screenplay I wrote) as a pitch for a feature.
I'm shooting on a Canon 60D, and I have the latest version of Magic Lantern installed. The only Magic Lantern setting I'm using is the cropmarks overlay, so I can see the camera LCD in the cinescope aspect ratio. Everything else outside of the Overlay tab hasn't been touched at all, it's the firmware default.

I'm getting this weird blue where (I assume) there should be total black. I've noticed it on the edge of a bowel, inside a coke can etc. but it's most noticeable when shooting these drawings (as shown below). Since I'm also new to the 60D I don't know if it's an ML issue or an issue with the 60D's settings.

It's not a software issue as the files look like that straight out of the camera, they look like that in Sony Vegas and they look like that after being exported.

However, I do notice that they slightly flicker on the page when the pencil is pressed down. Could this maybe be a reflection issue with the lights I'm using in that location? I'm not using any special lights, they're just the ones that are in the kitchen all the time. The flickering isn't noticeable unless I watch it on my 21inch screen (full screen) or larger.

Here's sample shots of what I mean:

The blue lines:



The flicker of the blue lines: (watch the arm in the drawing)





Can anyone offer a little bit of help as to how to get rid of this or what it might be?

(I only notice the colour difference now, that's because the very first image is from the colour corrected final product. And the other two images are SOOC)

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Strange blue in place of black
« on: July 13, 2013, 11:19:22 PM »

crazyrunner33

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Re: Strange blue in place of black
« Reply #1 on: July 14, 2013, 08:41:15 PM »
That my friend is aliasing.  It exists on most on every generation 1 HDSLR camera from Canon.  Pretty much all the DSLR cameras from Canon are still generation 1 in terms of video, except for the 5D Mark III.  The cameras are downsampling the sensor by skipping every 3 pixels, as a result there is a physical gap and it is allowing for aliasing and moire patterns.  The 5D Mark III downsamples the sensor using a more modern method, I assume it's just averaging out the values from the pixels in an area instead of picking one pixel.

To avoid this as much as possible you will need to turn down in camera sharpening all the way, or shoot ever so slightly out of focus. 

Stewbyyy

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Re: Strange blue in place of black
« Reply #2 on: July 14, 2013, 09:09:43 PM »
That my friend is aliasing.  It exists on most on every generation 1 HDSLR camera from Canon.  Pretty much all the DSLR cameras from Canon are still generation 1 in terms of video, except for the 5D Mark III.  The cameras are downsampling the sensor by skipping every 3 pixels, as a result there is a physical gap and it is allowing for aliasing and moire patterns.  The 5D Mark III downsamples the sensor using a more modern method, I assume it's just averaging out the values from the pixels in an area instead of picking one pixel.

To avoid this as much as possible you will need to turn down in camera sharpening all the way, or shoot ever so slightly out of focus.


Oh right, I wasn't aware aliasing could cause a colour change? I've never seen any examples of it that looked like this. This is the only time this has happened so far on the shoot as well, and I've shot in 6 locations now. It just seemed to happen a lot in this kitchen. Here's the film where it can be seen in the kitchen scene (around 6 minutes), it just pops up in random places there but nowhere else:
The Untold Story :: Short Film Small | Large


I would have expected it to show up in other locations where there are more finer details, such as pages of a book, writing on a page etc. I just find it odd how random it seems to be.

I already have the in camera sharpening all the way down. Pretty unfortunate this, I guess, oh well.

AAPhotog

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Re: Strange blue in place of black
« Reply #3 on: July 14, 2013, 11:37:27 PM »
Im glad someone else pointed it out, because to me, it looks as though she just used a blue pencil on that portion
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paul13walnut5

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Re: Strange blue in place of black
« Reply #4 on: July 15, 2013, 05:25:52 AM »


To avoid this as much as possible you will need to turn down in camera sharpening all the way, or shoot ever so slightly out of focus.

Em.  Naw.

What is shooting ever so slightly out of focus?  Shooting with something else in focus?  So where is the viewers attention going to be drawn to?  Away from your intended 'slightly out of focus' subject, that's for sure.

And once focus is out it is very hard to put it back in.  With large sensor cameras it is imperitive to nail focus.  Especially as they are potentially going to be shown on large to very large HD LCD's etc.

I don't know where you picked up this kernal of advice, but you should never ever repeat it ever again.

OP.

1.  Shoot in focus.

2. Advice to reduce in-camera sharpening is good.

3. You can get mirrorbox insert filters which help to combat aliasing, although they are cumbersome to use and expensive.

4. The 5D3 is probably the best sorted DSLR for video at the moment, but that isn't very helpful as you are already shooting with an alternative, and besides, not everybody can afford such an expensive camera, don't be fooled that the 5D3 is moire proof.. no camera is.

5. You can fix 98% of bad moire and aliasing in post, I'll now go into some detail how.

You are making a short film so I am going to assume you are going to be doing some editing.  I don't know your level of competancy with any particular suite, or your technical knowledge of video in general, unfortunately it is fairly technical and dry, I'll try and be as straightforward as possible, if you need any elaboration at all, please ask here, or PM me.

I use legacy Final Cut and Premiere, I'm going to speak in legacy final cut terms, which should be largely interchangable with your suites terminology.

FOR ALL your footage:  make sure it is interpreted or transcoded as progressive. 

YOUR SEQUENCE:  use a progressive codec.

OUTPUT: Make sure you take control of any further encoding be it to H264 for web or MPEG for Blu-ray or DVD, where the option exists keep it progressive.

Mismatches between interlaced and progressive can introduce aliasing where there was none, and make any pre-existing aliasing 10x worse.  So keep it progressive as far as you are able from shoot to capture to edit to output.

I am in the habit of putting a blanket .5 pixel guassian blur over my timeline.  If a particular shot has really bad aliasing I may go to .75 or even a full pixel for that particular shot.  It's a funny thing, that .5 isn't really noticed except by it's absence.  it won't make your footage soft, just a bit less 'video'.

Where there are zones of pronounced aliasing or moire I will create a duplicate upper layer and heavily apply MarvelsDSLR filtering and sometimes a heavier hand of guassian blur (maybe 1.5px) I would then garbage matte around the affected area with a feathered edge so that the unaffected areas can still be used.

Please please please don't ever shoot intentionally slightly out of focus, what is slight on a 3" LCD can be horrific on a 40" tv. 

JasonATL

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Re: Strange blue in place of black
« Reply #5 on: July 15, 2013, 11:24:56 AM »
Aliasing was my first guess on this, but I've rarely seen it show up as blue only - there has always been some red show up, too. But, it most likely is aliasing.

Since you said that you use Sony Vegas, here's another trick that you can try along the lines of what Paul has suggested:

Add a Chroma Blur fx to the image. This has the potential to do better than the suggested Gaussian Blur, since it only operates on the chroma, not luma. In your case, the aliasing is a color artifact, so the chroma blur might be sufficient. I'd experiment with the setting by starting with the 1 pixel and increasing to see if it improves. I've found that a 0.5 pixel (h and v) chroma blur actually works quite well, especially in front of a the Sharpen fx.

Stewbyyy

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Re: Strange blue in place of black
« Reply #6 on: July 15, 2013, 05:35:24 PM »


To avoid this as much as possible you will need to turn down in camera sharpening all the way, or shoot ever so slightly out of focus.

Em.  Naw.

What is shooting ever so slightly out of focus?  Shooting with something else in focus?  So where is the viewers attention going to be drawn to?  Away from your intended 'slightly out of focus' subject, that's for sure.

And once focus is out it is very hard to put it back in.  With large sensor cameras it is imperitive to nail focus.  Especially as they are potentially going to be shown on large to very large HD LCD's etc.

I don't know where you picked up this kernal of advice, but you should never ever repeat it ever again.

OP.

1.  Shoot in focus.

2. Advice to reduce in-camera sharpening is good.

3. You can get mirrorbox insert filters which help to combat aliasing, although they are cumbersome to use and expensive.

4. The 5D3 is probably the best sorted DSLR for video at the moment, but that isn't very helpful as you are already shooting with an alternative, and besides, not everybody can afford such an expensive camera, don't be fooled that the 5D3 is moire proof.. no camera is.

5. You can fix 98% of bad moire and aliasing in post, I'll now go into some detail how.

You are making a short film so I am going to assume you are going to be doing some editing.  I don't know your level of competancy with any particular suite, or your technical knowledge of video in general, unfortunately it is fairly technical and dry, I'll try and be as straightforward as possible, if you need any elaboration at all, please ask here, or PM me.

I use legacy Final Cut and Premiere, I'm going to speak in legacy final cut terms, which should be largely interchangable with your suites terminology.

FOR ALL your footage:  make sure it is interpreted or transcoded as progressive. 

YOUR SEQUENCE:  use a progressive codec.

OUTPUT: Make sure you take control of any further encoding be it to H264 for web or MPEG for Blu-ray or DVD, where the option exists keep it progressive.

Mismatches between interlaced and progressive can introduce aliasing where there was none, and make any pre-existing aliasing 10x worse.  So keep it progressive as far as you are able from shoot to capture to edit to output.

I am in the habit of putting a blanket .5 pixel guassian blur over my timeline.  If a particular shot has really bad aliasing I may go to .75 or even a full pixel for that particular shot.  It's a funny thing, that .5 isn't really noticed except by it's absence.  it won't make your footage soft, just a bit less 'video'.

Where there are zones of pronounced aliasing or moire I will create a duplicate upper layer and heavily apply MarvelsDSLR filtering and sometimes a heavier hand of guassian blur (maybe 1.5px) I would then garbage matte around the affected area with a feathered edge so that the unaffected areas can still be used.

Please please please don't ever shoot intentionally slightly out of focus, what is slight on a 3" LCD can be horrific on a 40" tv.

Some great, very informative advice there. Very helpful! Thank you! Some of it hasn't solved the problem but it will definitely be advice I'm adhering to in the future.

Aliasing was my first guess on this, but I've rarely seen it show up as blue only - there has always been some red show up, too. But, it most likely is aliasing.

Since you said that you use Sony Vegas, here's another trick that you can try along the lines of what Paul has suggested:

Add a Chroma Blur fx to the image. This has the potential to do better than the suggested Gaussian Blur, since it only operates on the chroma, not luma. In your case, the aliasing is a color artifact, so the chroma blur might be sufficient. I'd experiment with the setting by starting with the 1 pixel and increasing to see if it improves. I've found that a 0.5 pixel (h and v) chroma blur actually works quite well, especially in front of a the Sharpen fx.

The chroma blur has actually made a huge difference, it hasn't removed all of it but has made an extremely noticeable difference, it's not nearly as pronounced anymore.  Thank you very much!

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Re: Strange blue in place of black
« Reply #6 on: July 15, 2013, 05:35:24 PM »

paul13walnut5

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Re: Strange blue in place of black
« Reply #7 on: July 15, 2013, 06:46:11 PM »
The aliasing only really appears (to my eye) on the static shot, the locked off shot.

You could go a step further and create a new layer, desaturate it and then apply garbage matte close around the affected area to revel the colour outwith the paper?

mkabi

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Re: Strange blue in place of black
« Reply #8 on: July 15, 2013, 10:48:00 PM »
Have you tried changing the K value (white balance)?

I'm just saying because its not just the black that is blue.
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paul13walnut5

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Re: Strange blue in place of black
« Reply #9 on: July 16, 2013, 05:00:29 AM »
Funny mkabi mentions that, in the video the whites seem fine, in the grabs a colour cast has been introduced.  Are the grabs from the material pre-grading perhaps?

Stewbyyy

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Re: Strange blue in place of black
« Reply #10 on: July 16, 2013, 11:30:17 AM »
The aliasing only really appears (to my eye) on the static shot, the locked off shot.

You could go a step further and create a new layer, desaturate it and then apply garbage matte close around the affected area to revel the colour outwith the paper?

Tried that, proved a bit too fiddly for my liking. The Chroma Blur and gaussian blur have worked well enough to where I'm happy with the results.

Have you tried changing the K value (white balance)?

I'm just saying because its not just the black that is blue.

It's the kitchen in my house, so I just tried other shots on my own with a cooler while balance to see if that made a difference but the results were mostly similar. I'm getting the same blue on the pencil on the page, the edges of the bowls in the press and the edges of the press door.

However, I don't get the problem when I'm using sunlight through the kitchen window. It seems to only happen when the lights in the kitchen are on.

Funny mkabi mentions that, in the video the whites seem fine, in the grabs a colour cast has been introduced.  Are the grabs from the material pre-grading perhaps?

The grabs and pre-grading. (well, the first grab is post-grading, the other two are pre-grading).
I'm struggling to remember to set WB when shooting as I'm so used to shooting photos in RAW, so there's quite a drastic change post-grading as I'm forgetting to set it in camera a lot.

JasonATL

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Re: Strange blue in place of black
« Reply #11 on: July 16, 2013, 04:04:54 PM »
However, I don't get the problem when I'm using sunlight through the kitchen window. It seems to only happen when the lights in the kitchen are on.

Hmmm. What kind of lights?

This now makes me wonder about your shutter speed. If it is set to 1/60 or higher, try 1/50 or even 1/40.

Edit: Never mind. This doesn't really flicker that much. But, I still wonder about the lights. This is odd...
« Last Edit: July 16, 2013, 04:07:29 PM by JasonATL »

Stewbyyy

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Re: Strange blue in place of black
« Reply #12 on: July 16, 2013, 07:05:39 PM »
However, I don't get the problem when I'm using sunlight through the kitchen window. It seems to only happen when the lights in the kitchen are on.

Hmmm. What kind of lights?

This now makes me wonder about your shutter speed. If it is set to 1/60 or higher, try 1/50 or even 1/40.

Edit: Never mind. This doesn't really flicker that much. But, I still wonder about the lights. This is odd...

Shutterspeed is a 1/50th, shooting 1080p, 24fps.

No clue what kind of lights they are unfortunately, all I know is that they're fluorescent tubes. More disorientating than any other fluorescent lights I've seen though. They were recommended by the builder when we were getting the kitchen done up, we asked for powerful lights as our kitchen gets a lot of use for multiple things and we usually have dark days 95% of the time here in Ireland (doesn't help that the sun is on the front of the house and not the back where the kitchen is), so he said these were the most powerful he'd be able to put in.
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Re: Strange blue in place of black
« Reply #12 on: July 16, 2013, 07:05:39 PM »