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Fuzzy renders when downscaling RED 4k to HD
I’ve edited a short film shot on RED 4k, I roughly color corrected using the RED metadata (through the File Format Properties in the project media window).
Then I’ve rendered the project to the AVID DNxHD codec for quicktime (1080p, 10 bit) to pass it on for further postproduction which will be done on an Apple system.
Now the HD-render doesn’t come out very sharp. What could cause this?The RED material is loaded in an HD project (1920x1080p, 25 fps, Best quality, 8-bit, no deinterlace). I’ve rendered to BEST quality assuming the resize would be handled better. Can the unsharpness be due to the quality of the resize algorithm? I know Vegas has Bicubic/Bilinear, while the Lancosz algorithm would be better for downscaling, but don’t know of a way to make a Lancosz resize in Vegas (especially now that Frameserver and PluginPac adapter don’t seem to work anymore in Vegas 11).
I did a bit of testing and compared rendering to BEST with rendering on GOOD quality. Then it seems to be a bit more grainy and noisy, but I wouldn’t call that sharp either.
I also tried rendering it in a 32bit floating point project. There’s no noticeable difference (probably because the color-correction was done on the metadata level).
The only way I found to get a sharper image is putting a sharpness filter on the VideoBus, but I guess that is a fake sense of sharpness that would’nt keep all the richness in my source material (?)Does anybody know the best method or a workaround to get a sharp HD render of this kind of material from Vegas?
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10 Replies
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Have you tried setting your project to 4K and then just render to 1080p. I’m not sure it will make a difference but it’s worth a try if you haven’t already.
~jr
http://www.johnrofrano.com
http://www.vasst.com -
Hi John,
yes, I tried that too, and rendered from 4k project to BEST quality HD, but it gave no improvement. In the 4K project, the external monitor shows only a part of the image, in which you can see it’s quite sharp and crisp.After changing the project to HD, that sharpness is gone, the preview on the external monitor (at Best Full) has now the whole image, I’d expect it to give an even sharper/crisper impression, but it has become softer/fuzzier. I understand of courst that the resolution has gone down and detail gets lost, but the source never was an unsharp image, so why should the downscaled render be (slightly) unsharp..
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Well… the downscale gets fuzzy because you are blending pixels to cram more information into a smaller space. It’s not uncommon to add some sharpening to compensate for this. Don’t forget, 4k is 12 million pixels and HD is 2 million!!! so you are reducing by 6x. That’s a lot!
~jr
http://www.johnrofrano.com
http://www.vasst.com -
It doesn’t seem right. Shouldn’t it be possible to render a sharp lowres image from a sharp highres image ?
Imagine there are a red square and a white square next to each other, with a razor-sharp border, so that in the 4k image one pixel is full red, and it’s direct neighbour is full white), how can it be then that in the downscaled HD image the color transition is not sharp anymore, but spread over (let’s say) four pixels (full red, reddish pink,whitish pink, white) resulting in an unsharp borderline. The unsharpness would then not imply ‘because of the smaller space there is less information’, but: ‘there’s more information spread out over a bigger space’.
I get the impression there’s something wrong with the way Vegas downscales… -
Same reason a 720 x 480 downscale from 1920 x 1080 looks worse then the original footage. You can’t get rid of 4-6x the pixels and expect the same resolution.
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[Arthur Bueno] “Shouldn’t it be possible to render a sharp lowres image from a sharp highres image ?”
Given the proper scaling algorithm yes… using bicubic.. probably not.
[Arthur Bueno] “Imagine there are a red square and a white square next to each other, with a razor-sharp border, so that in the 4k image one pixel is full red, and it’s direct neighbour is full white), how can it be then that in the downscaled HD image the color transition is not sharp anymore, but spread over (let’s say) four pixels (full red, reddish pink,whitish pink, white) resulting in an unsharp borderline.”
Becase pixels are blended, not thrown away. The more you blend the worse it gets. At a 2x resize it’s probably still pretty sharp. At a 6x resize it’s 1 pixel representing what use to be 6 pixels! That’s not going to be sharp.
[Arthur Bueno] “I get the impression there’s something wrong with the way Vegas downscales…”
You could always export as an image sequence at 4K and batch resize to HD with Photoshop and see if you get better results.
~jr
http://www.johnrofrano.com
http://www.vasst.com -
I did some testing:
Vegas on “Best’ gets a little bit fuzzy/ blurred,it looks a bit better with some sharpen filter.
On “Good” it seems a bit less blurry than on “Best”, but noise in the black background becomes a lot more visible.
I then rendered out to 4k uncompressed and resized within Virtual Dub with the Lancosz algorithm (that would also be possible through a frameserver, there’s a new version of Debugmode frameserver out for Vegas 11 btw, for a small donatian to the author). The result with the Lancosz alogrithm is considerably sharper then the two options before.
I also investigated MPEG streamclip, which is supposed to be good at downscaling. It looked good, but it totally changed the levels/gamma in the render to DNxHD.
I found some discussion on this issue at the reduser forum, they suggest to use the half-high (2K) red output instead of resizing, but that’s not an option for me, because I’ve been using Pan/Crop a lot in the project. -
[Arthur Bueno] “I then rendered out to 4k uncompressed and resized within Virtual Dub with the Lancosz algorithm (that would also be possible through a frameserver, there’s a new version of Debugmode frameserver out for Vegas 11 btw, for a small donatian to the author). The result with the Lancosz alogrithm is considerably sharper then the two options before. “
So it sounds like frameserving to VirtualDub and using Lancosz might be a viable option. Thanks for testing this out.
~jr
http://www.johnrofrano.com
http://www.vasst.com -
Yes, that was my conclusion too
My test and research also confirms to me that the downscaling capability of Vegas is not very good, not just from 4k to HD, but also from HD to SD (which a lot of people do, to produce dvd’s).
I hope Sony improves their downscaling algorithm. Or mybe some 3rd party plugin arrives (like the Virtual Dub Lancosz resize, or an OpenFX plugin) that can be put before pan/crop in the FX-chain. -
I wasn’t sure whether it was better to revive this old thread or start a new one. Has there been any new developments on how to better render 4K to HD? I’m working with 4K footage from a Sony a7sii, downscaling to MainConcept AVC/AAC, Sony Tablet 1080p. Not only am I losing detail, it’s crushing colors together, giving skin an airbrushed look. This is without any adjustments or color corrections between input and output. When I render to 4K, the detail and color stays the same. (I’m not viewing on a 4K monitor, so technically I shouldn’t be seeing so drastic a change, right?)
Recommendations for better quality?
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