GH4 Quality of GH4's 1080P modes vs. GH2 and GH3?

[Thomas Smet]

4k to 1080 isn't as much about detail and sharpness as it is about clean quality and eliminating the limitations of a single sensor design. Like it or not all the GH cameras were 4k cameras with a down converted 1080recording. It is just that the pixel binning process isn't always the best method and doesn't preserver as much of the detail.

The reason why some of the sample 4k footage out there may look so sharp is because a lot of people are shooting at normal sharpness settings. With 4k if you shoot with the sharpness all the way down this will help. All the GH cameras have a certain level of electronic sharpness added to m4/3 lenses. This may also explain why a lot of the current sample out there look more videoish. Again dropping the sharpness level may help a bit.

It is always easy to drop detail in post. Adding detail is impossible. Starting with the cleanest image possible and soften for taste will give you better consistent results.

 

[TheDingo]

It's just not a true, super-clean image like the 4K mode or like the current standards i.e. C100

I think it is when you down-rez GH4 4K to 1080p, but not when you shoot native GH4 1080p footage.

I would like to see a proper comparison of 200 Mbps ALL-I with down-rezzed 4K footage to see what the differences are. ( rolling shutter will probably be the biggest difference )

 

[Cosimo Bullo]

"I think it is when you down-rez GH4 4K to 1080p, but not when you shoot native GH4 1080p footage."

Exactly.

The 1080 Ext tele is very clean, by the way. No aliasing/moire. But not a super sharp image as it's pixel to pixel from the sensor.

 

[Lpowell]

I'm getting much better results when I down-rez the same 4K footage to 1080p using Sony Vegas Pro 11. I am down-rezzing using the free Cineform CODEC, which may have something to do with the results I am seeing, but on my end of things down-rezzed GH4 4K footage looks outstanding at 1080p when the Cineform CODEC is used.

Two separate systems interact here to produce the final result, and your mileage may vary depending on how each system is fine-tuned. The downscaling from 4K to 1080p is done by your editor, in this case Sony Vegas. I'm more familiar with After Effects, and its project settings are crucial in determining the quality of the downscaled results. The most important thing is to import the footage in a 32-bit floating point color space, where fractional downscaling details will not be truncated. The next issue is to carefully evaluate the degree of sharpening used in the downscaling algorithm, and this is often a subjective judgment.

One of the things that makes Cineform a great intermediate codec is its use of wavelet compression rather than macroblocks. This eliminates the ugly rectangular artifacts that so often contaminate H.264 video. These inherent artifacts can sometimes be exaggerated when you re-encode a video captured in H.264 a second time with another H.264 encoder, even when using a higher bitrate. When exporting a 32-bit project to Cineform, be careful to verify that your editor is outputting the video data in 10-bits rather than 8-bits. With a Quicktime MOV export, After Effects defaults to 8-bit color depth (the "Millions of Colors" option), and Cineform must be configured to enable 10-bit mode (the "Trillions of Colors" option). When done properly, you'll get a Cineform file containing a downscaled 1080p video in 10-bit 4:2:2 color depth.

 

[Phil_D]

Hi

I think by the time we've gone 4K to 1080P and exported it to a lossy but play friendly codec for delivery, the end result doesn't seem that different than just starting out with good 1080P. A lot of the praise for 4K to 1080P seems to be based on playing 4K but having it downscaled by the media player to 1080P in real-time. In essence we are then watching something similar to uncompressed 1080P, with I suspect the media player adding sharpening as they would do if going from smaller to larger.

Take that 4K and export as 1080P and encode to H264 so it can be put someone for playback, and those advantages are now gone and it's a more an even playing field.

There is also a paradox here, how can a lossy encoding at 100Mbps at 4K, contain more picture information than the same 100Mbps at 1080P? Would an 8K video at 100Mbps produce a better 4K video when downsized and even better 1080P? Also if we use 4K to crop and pan, and use a quarter of the 4K image on some scenes to produce a full frame 1080P sequence, than that 1080P sequence has been captured at around 25Mbps, and depending on the footage then we could expect that to look pretty bad.

So as always still pros and cons. 4K lets you zoom, crop and pan on the timeline, 1080P native on the GH4 gets you 60fps and easier to edit files.

Regards

Phil

 

[Thomas Smet]

Hi

I think by the time we've gone 4K to 1080P and exported it to a lossy but play friendly codec for delivery, the end result doesn't seem that different than just starting out with good 1080P. A lot of the praise for 4K to 1080P seems to be based on playing 4K but having it downscaled by the media player to 1080P in real-time. In essence we are then watching something similar to uncompressed 1080P, with I suspect the media player adding sharpening as they would do if going from smaller to larger.

Take that 4K and export as 1080P and encode to H264 so it can be put someone for playback, and those advantages are now gone and it's a more an even playing field.

There is also a paradox here, how can a lossy encoding at 100Mbps at 4K, contain more picture information than the same 100Mbps at 1080P? Would an 8K video at 100Mbps produce a better 4K video when downsized and even better 1080P? Also if we use 4K to crop and pan, and use a quarter of the 4K image on some scenes to produce a full frame 1080P sequence, than that 1080P sequence has been captured at around 25Mbps, and depending on the footage then we could expect that to look pretty bad.

So as always still pros and cons. 4K lets you zoom, crop and pan on the timeline, 1080P native on the GH4 gets you 60fps and easier to edit files.

Regards

Phil

Not true. This assumes the pixel process is perfect when shooting native 1080. the 4k itself when converted to 1080 will always be 1080. No magic there. What you do gain however is a better method of getting that sensor down to a 1080 video. Pixel binning in the GH camera can cause moire artifacts. Remember the GH cameras are essentially already 4k cameras. Always have been including the GH1. The sensors were larger than 4k. Since the camera couldn't do anything with all that data they had to convert the sensor readout to 1080. The cameras could not do a true down conversion 60 or 24 times a second so a process called pixel binning is used. This process does a very good job and helps reduce sensitivity and reduce noise but it isn't perfect.

By doing the down conversion in post you are not magically keeping 4k resolution. What you are doing to using a more accurate process to down convert the video with cleaner more consistent results. Even delivering to Blu-ray will keep this advantage because it is about how all of the those pixels are created in the 1080 frame and nothing at all to do with image compression. It has nothing to do at all about the delivery format but how the 1080p image is formed and processed. Without a doubt shooting 4k and delivering 1080p will give you cleaner results because you are eliminating the pixel binning step.

 

[Phil_D]

HI

Not true. This assumes the pixel process is perfect when shooting native 1080. the 4k itself when converted to 1080 will always be 1080. No magic there. What you do gain however is a better method of getting that sensor down to a 1080 video. Pixel binning in the GH camera can cause moire artifacts. Remember the GH cameras are essentially already 4k cameras. Always have been including the GH1. The sensors were larger than 4k. Since the camera couldn't do anything with all that data they had to convert the sensor readout to 1080. The cameras could not do a true down conversion 60 or 24 times a second so a process called pixel binning is used. This process does a very good job and helps reduce sensitivity and reduce noise but it isn't perfect.

By doing the down conversion in post you are not magically keeping 4k resolution. What you are doing to using a more accurate process to down convert the video with cleaner more consistent results. Even delivering to Blu-ray will keep this advantage because it is about how all of the those pixels are created in the 1080 frame and nothing at all to do with image compression. It has nothing to do at all about the delivery format but how the 1080p image is formed and processed. Without a doubt shooting 4k and delivering 1080p will give you cleaner results because you are eliminating the pixel binning step.

I understand exactly what you are saying, however when I've gone 4K to 1080P then rendered that to a delivery codec the difference isn't that noticable, certainly not when played on a 1080P TV sat back at typical viewing distances, I've done an A/B comparison and asked family members their views on which is the best picture and no one can tell a difference. Maybe I need some more challenging footage to make it more obvious.

I also don't understand why Panasonic hasn't taken the same approach with 1080P, they could take the same 4K crop and convert that to 1080P very easily giving the same result, isn't this the reason for 4K for TV being 3960 X 2160 is the ease and artifact free way 4K will down scale to 1080P (all even numbers), unless of course they can't read out all those pixels fast enough from the sensor for 60P yet, presumably that is the issue.

Interesting times, gives us all more options.

Regards

Phil

 

[TheDingo]

I think by the time we've gone 4K to 1080p and exported it to a lossy but play friendly codec for delivery, the end result doesn't seem that different than just starting out with good 1080p.

The "lossy but play friendly CODEC" will still benefit from ultra-clean 1080p, which you can only obtain from higher end prosumer cameras or shooting with the few 4K consumer cameras and down-rezzing to 1080p.

With a good display system, full resolution 1080p looks gorgeous.

 

[TheDingo]

I've done an A/B comparison and asked family members their views on which is the best picture and no one can tell a difference

I've done A/B comparisons with corporate clients, and some people had trouble telling high quality 480p from high quality 1080p. ( I have a brilliant graphic designer friend who bought one of the first Sony 55 inch HD sets when they came on the market, and spent a year watching everything in 480p mode until I came over for dinner one night and immediately enabled 1080p mode )

Image quality may not matter to my audience, but it matters to me.

 

[Phil_D]

Hi

The "lossy but play friendly CODEC" will still benefit from ultra-clean 1080p, which you can only obtain from higher end prosumer cameras or shooting with the few 4K consumer cameras and down-rezzing to 1080p.

With a good display system, full resolution 1080p looks gorgeous.

It does indeed look gorgeous, the results look gorgeous watching from normal TV viewing distances regardless if I've gone 4K to 1080P or from native 1080P, nose up against a calibrated computer monitor you might say yes, I can see that looks better, but sat at normal viewing distances from a TV so far no one I've asked to judge has noticed the difference.

You should see our broadcast HD quality in the UK, it's not even full HD but 1440x1080 so has to be scaled and lucky if it hits 6Mbps, anything compared to that looks drop dead gorgeous, so we are easily pleased over here :cheesy:

Regards

Phil

 

[Lpowell]

I think by the time we've gone 4K to 1080P and exported it to a lossy but play friendly codec for delivery, the end result doesn't seem that different than just starting out with good 1080P.

The big advantage to shooting 4K->1080p is increased latitude in post-processing. If you are doing any kind of scaling or full-frame image manipulation, you will get finer results starting with 4K rather than 1080p. The delivery codec is just the final step in the process. Your workflow needs to maintain higher image quality standards in order to achieve the best possible results from the final render.

 

[ralfmouth]

Down-converted 4K footage (to my eyes) looks detailed enough to question the validity of 4K displays. By that token I don't question the validity of "4K" capture. Its necessary for true "2K" according to sampling theory and i've not yet seen any native 1080 to contradict that so far. But sure, it depends on viewing distance.

 

[Shenan]

Thanks everyone for your replies. The 4K modes of the GH4 are probably out for me in most cases because the worse rolling shutter in those modes will not do for my work (run and gun handheld documentary). Hence why I was asking about the native 1080p modes. It sounds like they're no worse than the GH3 at least in regards to moiré/aliasing (probably my main concern after rolling shutter), so the camera will probably work for me. Thanks!

 

[Thomas Smet]

HI



I understand exactly what you are saying, however when I've gone 4K to 1080P then rendered that to a delivery codec the difference isn't that noticable, certainly not when played on a 1080P TV sat back at typical viewing distances, I've done an A/B comparison and asked family members their views on which is the best picture and no one can tell a difference. Maybe I need some more challenging footage to make it more obvious.

I also don't understand why Panasonic hasn't taken the same approach with 1080P, they could take the same 4K crop and convert that to 1080P very easily giving the same result, isn't this the reason for 4K for TV being 3960 X 2160 is the ease and artifact free way 4K will down scale to 1080P (all even numbers), unless of course they can't read out all those pixels fast enough from the sensor for 60P yet, presumably that is the issue.

Interesting times, gives us all more options.

Regards

Phil

It is a subtle difference without a doubt but it is there. Of course native 1080 is still very high quality. You just clean up some of the sensor based artifacts by shooting 4k first. Very few may ever notice the difference but it is there if you do any form of image processing.

Where you will notice a difference is with shots that may have moire or aliasing artifacts. The 4k down conversion will be virtually clean of these type of issues. Very fine lines like power lines may also be cleaner and more accurate. Again an average Joe would hardly ever notice. Shooting a talking head may not show as much advantage but then again neither would shooting a talking head at 720p. You really need super fine detail to notice the down conversion difference.

Panasonic cannot do this type of down conversion because it is very process intensive for a processor inside of a camera to do that 60 times a second. Imagine scaling a jpeg in Photoshop and batching that 60 times and expecting it to finish in under a second. Now have it keep doing that for an hour while recording video. Your camera may explode or melt if it tried to do that. Just too many pixels to work with that fast. This is why the 4k mode grabs just the cropped 4096x2160 portion of the sensor instead of scaling the full sensor to 4k. It just doesn't have enough processing power to do all of that at once.

 

[Phil_D]

Hi

It is a subtle difference without a doubt but it is there. Of course native 1080 is still very high quality. You just clean up some of the sensor based artifacts by shooting 4k first. Very few may ever notice the difference but it is there if you do any form of image processing.

Where you will notice a difference is with shots that may have moire or aliasing artifacts. The 4k down conversion will be virtually clean of these type of issues. Very fine lines like power lines may also be cleaner and more accurate. Again an average Joe would hardly ever notice. Shooting a talking head may not show as much advantage but then again neither would shooting a talking head at 720p. You really need super fine detail to notice the down conversion difference.

Panasonic cannot do this type of down conversion because it is very process intensive for a processor inside of a camera to do that 60 times a second. Imagine scaling a jpeg in Photoshop and batching that 60 times and expecting it to finish in under a second. Now have it keep doing that for an hour while recording video. Your camera may explode or melt if it tried to do that. Just too many pixels to work with that fast. This is why the 4k mode grabs just the cropped 4096x2160 portion of the sensor instead of scaling the full sensor to 4k. It just doesn't have enough processing power to do all of that at once.

The process of downscaling from 4K to 1080P is very simple, and the camera already does this if you set HDMI to 1080 to monitor the recording. I think the main issue is the sensor isn't fast enough to support 4K at 60fps, therefore if downscaling to 1080 from the same 4K image, it would only support 30fps maximum and not 60fps.

I suspect these issues will be resolved for the GH5, I'll start saving now.

Regards

Phil

 

[Ian-T]

...
The reason why some of the sample 4k footage out there may look so sharp is because a lot of people are shooting at normal sharpness settings. With 4k if you shoot with the sharpness all the way down this will help. All the GH cameras have a certain level of electronic sharpness added to m4/3 lenses. This may also explain why a lot of the current sample out there look more videoish. .....

Made it this far in the thread and realized you said what I was going to say. Thank you.

I've seen at least one video in 4K that had sharpness turned all the way down...it had none of that flickering you see because of the overly sharp image at "0." I've also read that having at -3 is the optimal point. I'll just say it again for those that missed it...DONT SHOOT 4K AT "0" SHARPNESS IF YOU ARE GOING FOR A SMOOTH FILM-LIKE LOOK. I'll also add...using Panasonic wide lenses causes the cam to over sharpen the image because of its internal distortion correction feature. Manual lenses works wonders. this is true for all GH-X cameras.

 

[Thomas Smet]

Hi



The process of downscaling from 4K to 1080P is very simple, and the camera already does this if you set HDMI to 1080 to monitor the recording. I think the main issue is the sensor isn't fast enough to support 4K at 60fps, therefore if downscaling to 1080 from the same 4K image, it would only support 30fps maximum and not 60fps.

I suspect these issues will be resolved for the GH5, I'll start saving now.

Regards

Phil

No the processor uses pixel binning to convert the full sensor to HD before sending to the HDMI port. This is not the same as the type of software down conversion where all the pixel values are calculated based on neighboring values. Most DSLRs use pixel binning or line skipping to get a HD image. This introduces moire and aliasing and a loss of fine thin details. 4k only supports 30fps because that is still a massive amount of pixel data coming off of the sensor. It is already insanely impressive Panasonic was able to get 4k to work on the GH4 period. Just a year ago cameras could not process that much data from a sensor.

Keep in mind there is a lot of stuff going on in that processor. It is taking the RAW sensor bayer data and doing a debayer conversion on the fly to create the full sensor worth of color data. It then takes that new entire sensor data and uses pixel binning to convert it to 1920x1080. All of this happens at 60 fps on the GH3. On the GH4 it can happen at 96fps. Although I have a theory that the 96fps mode uses an even less accurate form of pixel binning which is why some people are reporting much lower quality with the 96fps mode. Perhaps the GH4 is using line skipping in order to speed up the processor to handle 96fps.

 

[Thomas Smet]

Made it this far in the thread and realized you said what I was going to say. Thank you.

I've seen at least one video in 4K that had sharpness turned all the way down...it had none of that flickering you see because of the overly sharp image at "0." I've also read that having at -3 is the optimal point. I'll just say it again for those that missed it...DONT SHOOT 4K AT "0" SHARPNESS IF YOU ARE GOING FOR A SMOOTH FILM-LIKE LOOK. I'll also add...using Panasonic wide lenses causes the cam to over sharpen the image because of its internal distortion correction feature. Manual lenses works wonders. this is true for all GH-X cameras.

This is one of those things that make RAW look the way it does. Sure it is RAW and uncompressed but a big part is the fact that there is zero sharpness added to the camera. If GH users want to get closer to that RAW look then they really should eliminate sharpness as much as possible. Single sensors that are de-bayered actually have a pretty soft image by nature. It is the sharpening that brings back some of that punchiness. Most cameras that sharpening happens in camera. When shooting RAW you do that in post. This is one of the single most important benefits to shooting 4k even for Hollywood big budget FX movies. Shoot RAW 4k or 5k and down convert to 2k to enhance the detail instead of trying to shoot 2k and add sharpness which looks fake. Best HD I ever shot was with 4k from a REDONE and processed through Assimilate Scratch with nice gaussian scaling. Some find it very soft but other forms of scaling formulas also enhance edges with sharpening. Same is true for 3D animation anti-aliasing rendering methods. The really detailed render methods actually add edge enhancement to the render. The cleanest 3D renders you can get are kind of soft as well. Just the nature of image processing. It is always a balance between detail and fake edge enhancement.

People tend to mistake acutance (sharpness) with resolution. They are not directly related to each other.

http://www.cambridgeincolour.com/tutorials/sharpness.htm

 

[vtwiz]

Down-converted 4K footage (to my eyes) looks detailed enough to question the validity of 4K displays. By that token I don't question the validity of "4K" capture. Its necessary for true "2K" according to sampling theory and i've not yet seen any native 1080 to contradict that so far. But sure, it depends on viewing distance.

Spot on. Ive been looking at video aquired in 4K and down resed to 1080p on a 1080p 50" IPS screen and the quality and detail is amazing. Definitely better than 1080p aquisition on a 1080p screen. No real need for 4k screens, at least not smaller than maybe 60".