I don't think that's correct. I think both are a straight crop of the sensor, but I would love to be proved wrong. Might you have a link to where you read that? It would be awesome if the UHD at 100mbps was a 2x crop factor. Cheers, Pete
GH4 The GH4 is here!
- Thread starter pulpfiction007
- Start date
I saw this mentioned several places when the GH4 was first announced. Here is a link to Andrew Reid's comments http://www.eoshd.com/content/11934/panasonic-gh4-preview
BitMaestro
Well-known member
I think we're all in agreement that Cinema 4k is cropped. The part of statement I believe Pete was questioning (and that I would also like to see a source for) is:
As an aside, even if the GH4 does use the whole width of the sensor, because this isn't a multi-aspect sensor, there's still an additional crop (of 9% or 2.18X total).
As a further aside, Andrew Reid's numbers are off:
First, the full width sensor resolution is 4608, not 4680.
Second, as noted further on in the old thread linked to above, you can only use horizontal resolution when the aspect ratio is the same, but this is obviously not the case when calculating crop factor for 16:9 video relative to a 3:2 photography frame.
The actual crop factor for Cinema 4k on the GH4 is ~2.5X (more precisely, 2.48X)
Mark
As an aside, even if the GH4 does use the whole width of the sensor, because this isn't a multi-aspect sensor, there's still an additional crop (of 9% or 2.18X total).
As a further aside, Andrew Reid's numbers are off:
First, the full width sensor resolution is 4608, not 4680.
Second, as noted further on in the old thread linked to above, you can only use horizontal resolution when the aspect ratio is the same, but this is obviously not the case when calculating crop factor for 16:9 video relative to a 3:2 photography frame.
The actual crop factor for Cinema 4k on the GH4 is ~2.5X (more precisely, 2.48X)
Mark
Last edited:
That's Better than EOS HD, but I work the crops out to be something different still.
You are right that aspect ratio plays a part in crop factors. A crop factor isn’t much use if it’s a ratio of diagonals from sensors with different aspects. That’s why you shouldn’t use DIAGONALS for the comparison. And is why it makes sense to actually ONLY use horizontals. The 35mm photography full frame is 2:3 ratio but if we use the horizontal we can just assume we are comparing to a 16:9 crop of the sensor. Since the video output of most cameras is usually always 16:9 the ratio of the horizontal is exactly the same as it would be for the diagonal were you to work it out.
In the case of cinema 4k we can assume it is compared to a 1.9:1 crop of the full frame sensor.
True, the diagonal ratio of cinema 4k to quad HD will be different to the horizontal ratio, but as long as we understand it is the horizontal angle of view we are comparing in this case, it is still a meaningful comparison.
Therefore the crop factors I make out are:
GH2 multi aspect in 16:9 = 1.91 (36 / 18.8)
Full sensor width regular 4/3rds = 2.08 (36 / 17.3)
GH4 in cinema 4k crop mode = 2.34 (36 / ((17.3/4608)*4096)
GH4 in Quad HD crop mode = 2.49 (36 / ((17.3/4608)*3840) (My assumption is that the GH4 will crop for quad HD as well as cinema 4k)
I'm pretty sure I've read the reverse in a few write-ups: that UHD will be an even further crop than C4K. Unfortunately I don't remember where I read this. Maybe I just inferred that from something else, but it makes sense that they would use the same manner of reading the sensor for both 4k modes, rather than processing them differently.
I remember reading this too, and it makes sense. If the sensor is 4608x3456 then it makes sense that UHD is cropped more than C4K. On Panasonics specs page for the GH4 it lists Cinema 4k as 4096x2160 and UHD as 3840x2160. This makes sense, too, as C4K conforms to the 1.85:1 aspect ratio for cinema and UHD is 16:9.
Moving this thread into a different direction, it just occurred to me that, since the GH4's sensor is actually 4:3, if a firmware upgrade allowed a 4k image from the full 4:3 sensor (4608x3456), you could use anamorphic lenses and shoot very high quality widescreen images. Stretching the images in post would yield a 2.39:1 image from a higher than 4k source. No cropping of the top and bottom. That could be very exciting!
You guys are engaging in uninformed speculation. There are plenty of ways to get a 3840x2160 frame from a 4608x3456 sensor without changing the horizonal crop factor. Take a look at the GH4 specs for still images. In 16:9 ratio, it can shoot jpegs at 4608x2592(L) / 3840x2160(M) / 1920x1080(S) at the standard 2.0 m43rds horizonal crop factor. So clearly the GH4 has the technical ability to (a) crop the full sensor to a 4608x2592 16:9 image with the standard 2.0 m43rds horizontal crop factor, and (b) downscale the 4608x2592 crop to 3840x2160 image or a 1920x1080 image with the standard 2.0 m43rds crop factor. If the GH4 can do it for stills, it is logically possible that it can do it for movies. We won't know for sure until the camera is released, but it is irresponsible to assert that the 4k horizontal crop factor will be greater than 2.0 at this point since all the empirical evidence points the other way.
http://www.panasonic.com/uk/consume...pact-system-cameras-dslm/dmc-gh4eb.specs.html
http://www.panasonic.com/uk/consume...pact-system-cameras-dslm/dmc-gh4eb.specs.html
I only come in at the end of this conversation so I don't know what other claims have been made, but I'm not saying that it's not technically feasible for them to do a full width readout and derive UHD from it. All that I'm saying is that Panasonic must have some good reason for deciding to go with a sensor crop for the C4K mode (probably either processing power or preventing artifacts, or a combination of both), so why would they not apply that same reasoning to the UHD mode, as it's much more similar to the C4K mode than to FHD?
Thomas Smet
Veteran
Because how do you bin 4608 into 4096 pixels? You would have to skip every 9th pixel which would look odd. This isn't a situation where you can really bin a block of pixels together because there is no block of pixels. Just a duplicate every 9th pixel or so. This isn't the same as scaling a 4608 wide image in Photoshop to 4096. Cameras have to use a faster process to down convert. For HD that happens to be binning. Binning just wouldn't work very well on 4k. In order to have a decent binning process for 4k you would need a lot more pixels.
Thomas, that's pretty much what I'm trying to say, in a different way. It doesn't make much sense for Panasonic to NOT do a 1:1 pixel readout for UHD, especially when it's agreed that they are doing it for C4K.
Personally, I'm happy as long as they use the most sensible solution from an engineering and image quality perspective. The crop factor is not so much of a factor for me anymore, not when there is the speedbooster. So we get MFT @ 1080P, or slightly larger than Super 35 @ 1080P (with speedbooster), or closer to Super 16 @ 4K, or slightly smaller than APS-C @ 4K (with speedbooster). Sounds great to me.
Personally, I'm happy as long as they use the most sensible solution from an engineering and image quality perspective. The crop factor is not so much of a factor for me anymore, not when there is the speedbooster. So we get MFT @ 1080P, or slightly larger than Super 35 @ 1080P (with speedbooster), or closer to Super 16 @ 4K, or slightly smaller than APS-C @ 4K (with speedbooster). Sounds great to me.
Last edited:
Binning is just a computationally simple way to downscale. It doesn't even give you the best image quality. And it's certainly not the only way. How can the GH4 shoot 3840x2160 or 1920x1080 JPEGs that preserve the 2.0 horizontal crop factor? Did you even read my post?
Thomas Smet
Veteran
Because those are still images which require different processing than processing video 24,30 or 60 frames per second. This is one of the reasons why DSLR's cannot shoot burst photography at 24, 30 or 60 fps. Burst photography usually caps out at 7 to 10 fps which is all the heavier processing can handle. No DSLR can down sample video the same way it does for stills. The GH4 can shoot video at 4k at 24fps but cannot shoot stills at that same speed or anywhere near that speed.
Its true that it can downscale a single frame "intelligently" but it may be a step too far for the processor to do it 30 times per second. I would imagine the jpeg burst rate (which seems to be 12fps) is a good indication of the processors limit.
Last edited:
BitMaestro
Well-known member
That is exactly backwards. See the discussion in the other thread. Specifically, Barry Green's post #21.
And all Pete and I were asking is if you could give us a link to any of these other writers (because at least I haven't read that anywhere).
This is where you may be getting confused. As noted in my previous post in this thread (and explained in detail in the old thread/post I linked to), since the GH3 (and GH4) do not have multi-aspect sensors, they do not have the standard m4/3 2.0 crop factor when shooting stills in any other aspect ratio than 4:3. Yes, the horizontal resolution doesn't change, but the crop factor most certainly does, because the diagonal most certainly does, which gets back to why you have to use the diagonal measurement when comparing different aspect ratios.
Barry_Green
Moderator
Just to underscore the point -- if the aspect ratios are different, you must use the diagonal to compare them. If the aspect ratios are the same, then you can compare using the horizontal width (or vertical width, doesn't matter).
Ok, so here are the amended crop factors using diagonals for cinema 4k.
All are now correct compared to full frame 16:9.
GH2 multi aspect in 16:9 = 1.92 (36 / 18.68)
Full sensor width regular 4/3rds = 2.08 (36 / 17.3)
GH4 in Quad HD crop mode = 2.49 (36 / ((17.3/4608)*3840) (My assumption is that the GH4 will crop for quad HD as it would make no sense to just crop with cinema 4k)
GH4 cinema 4k = 2.37 (41.3/17.38)
Uwe Lansing
Veteran
I don´t know if this has already been posted somewhere:
http://www.bestmirrorlesscamerarevi...h4-leica-15mm-and-nocticron-425mm-at-the-tps/
3 original native 4k-clips:
https://drive.google.com/folderview?id=0B6OHIUZ9PCvNbjBEZURGQnAyVlk&usp=sharing#list
http://we.tl/tX9w9alJni
http://www.bestmirrorlesscamerarevi...h4-leica-15mm-and-nocticron-425mm-at-the-tps/
3 original native 4k-clips:
https://drive.google.com/folderview?id=0B6OHIUZ9PCvNbjBEZURGQnAyVlk&usp=sharing#list
http://we.tl/tX9w9alJni
Last edited: