GH4 striped shirt flickering/flashing in GH4 capture

S

spaulgal

Well-known member
Greetings.

We have shot a ton with this camera... and I have not seen this issue before.

We have a subject who is wearing a striped shirt, and it is flickering and flashing a ton.

In the old days we would have avoided these types of clothes/textures, but the GH4 has been so solid for us and we have not paid close attention to what on camera people wear as much of late.

GH4; V-LOG; 100mbps; FCP X; The shirt texture is quite bad-- very tight horizontal stripes.

We've tried all the output and timeline options, all seem to render the same

We always sharpen our footage slightly in post. It's obviously better with sharpening turned off.

Any pointers on how to best salvage the footage would be great!
 
spaulgal said:
Greetings.

We have shot a ton with this camera... and I have not seen this issue before.

We have a subject who is wearing a striped shirt, and it is flickering and flashing a ton.

In the old days we would have avoided these types of clothes/textures, but the GH4 has been so solid for us and we have not paid close attention to what on camera people wear as much of late.

GH4; V-LOG; 100mbps; FCP X; The shirt texture is quite bad-- very tight horizontal stripes.

We've tried all the output and timeline options, all seem to render the same

We always sharpen our footage slightly in post. It's obviously better with sharpening turned off.

Any pointers on how to best salvage the footage would be great!
Click to expand...


This is called moire, and it happens in life with your eyes as well as with cameras. Each camera has a different spatial resolution, so depending on your focal length, the pattern, and your monitoring resolution- you may or may not see this.

When in doubt monitor in full resolution.

Sometimes it's easier to re-shoot than fix this problem. If you can't re-shoot, then you need to figure out what kind of moire it is. This has been well covered on the internet, and if you search for something like "moire fix post" you should be able to find some steps that will lead you to your possible solutions.

Start by checking your color channels, some moire may only be in one channel, and then you can plan accordingly. You could also invest in a professional post facility if you have more money than time to fix this. I can recommend a few if you are stuck. You'll want a post house well versed in VFX and color correction.
 
I know, I don't even think about it with the GH4 - I haven't seen moire yet!

You've probably already thought about this but can you punch in to where the shirt can't be seen? That seems like the fastest fix if you can get away with the interview being that tight.
 
I've got moire once when shooting uhd. It was on a shirt that a presenter wore and it was not pretty! I was really surprised to see it though. I thought that GH4 was more or less moire free...
 
In two years of regular shooting I have only once seen a tiny bit of moire when shooting in 4K UHD mode, and so far I've never seen it when shooting in 4K DCI mode.

I know that if I shoot in 1080p mode I will often see moire in my shots, thus I NEVER shoot in 1080p mode with my GH4, I always shoot in 4K.
 
TheDingo said:
In two years of regular shooting I have only once seen a tiny bit of moire when shooting in 4K UHD mode, and so far I've never seen it when shooting in 4K DCI mode.

I know that if I shoot in 1080p mode I will often see moire in my shots, thus I NEVER shoot in 1080p mode with my GH4, I always shoot in 4K.
Click to expand...

To me the #1 reason to shoot in 4K, as this trademark of DSLR FHD video is instantly visible to everyone viewing - not just those with nose on the monitor looking for ISO 200 noise. And dropping it on a 1080p timeline seems to matter little.

Now, on to handling rolling shutter skew as the other 500# gorilla in the shadows. Hoping thet the GH5's necessarily faster sensor readout for 4K 60p mode translates into improvement here in 4K 30/24p.
 
High frequency data can still be a problem when shooting UHD. At a certain point what is in front of the camera will have fine detail that falls in between the pixels of the GH4. A softer image helps here and what you have the camera sharpness at and what sharpness you add in post will affect it. Sharpness adds contrast to an image to give the illusion it is sharper. It takes the natural roll off between the pixels and crushes it so the change between each pixel is more sudden. This makes the details look sharper. By doing this however you make very fine detail bounce too much between the fine UHD pixels.

The way to combat high frequency detail is to soften the image. Shooting at a -5 sharpness can help. -5 is closer to what the sensor actually sees. After debayering and low pass filtering what the sensor gets is typically rather soft. Raw cameras don't look soft because somebody wanted soft looking footage. They look soft because the nature of raw is that it isn't touched by the camera. All cameras add a level of sharpness to an image. I suspect the GH4 even at a -5 sharpness is still adding a certain amount of sharpening which can cause moire in very rare situations when the detail is too high of a frequency. Especially if you use native m43 lenses which are corrected in the camera.

A digital image made up of a grid of pixels needs to have a certain level of softness or it displays high frequency artifacts when in motion. Still photos don't really see it which is why some DSLRs are now removing their low pass filters and when it comes to video the scaling is providing some of the needed filtering.
 
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