Blackmagic Pocket Cinema Camera 4K gets BRAW in extensive FFPGA hardware update delivered via software

[amanieux]

1 hour ago, Emanuel said:

No man, it was not involuntary at all : D I am joking with the terminology because they actually mean the same : )

don't want to split hairs but "lossy compression" can be  "visually lossless" or "visually lossy" , "lossless compression" is unambiguous because it means compression which does not change a single bit from the uncompressed data so it is visually indistinguishable because it is identical 

[amanieux]

On 3/11/2019 at 1:25 PM, Mattias Burling said:

The definition of raw isn't that its uncompressed. Its that its not yet processed and is just a file with the code needed to create the image. So no, compressed raw, lossless or lossy is not bullshit raw. Its still raw.

(BTW, its not "RAW", its "raw" or "Raw" if its in the beginning of a sentence.)

sorry you contradict yourself, you say the definition of raw is that its "data not yet processed" and then you say" lossy raw is still raw" but lossy compression is a "processing" of the original data and not a "minimal processing" it is a "heavy processing" involving very complex algorithms

what i don't get is that blackmagic could have minimized this BRAWgate but just adding a BRAW 1:1 consisting only of the uncompressed raw data for users who want maximum quality no matter the file size as i am sure there is no possible patent litigation involved on serializing data in a file, any coder can code that in 5 minutes. it is a step down from losless cinemadng raw because it is the exact same data but in a bigger file size but it is better than having nothing if they really have a patent claim litigation to avoid. they perfectly know their users are pixel peeper, how could they think they could get away with it with just a BRAW powder in the eyes ?

and you you are correct it was my mistake : "RAW" is not an acronym so we should rather write "raw" or "Raw" if its in the beginning of a sentence

[Emanuel]

1 hour ago, amanieux said:

don't want to split hairs but "lossy compression" can be  "visually lossless" or "visually lossy" , "lossless compression" is unambiguous because it means compression which does not change a single bit from the uncompressed data so it is visually indistinguishable because it is identical 

LOL Good one! : -) I loved that one! Now we're talking! : )

1 hour ago, Papiskokuji said:

So I tried a bit of BRAW. I'm not too worried about the very slight loss in sharpness everybody's talkin' about. I actually kind of like the braw management tab in Resolve. The only thing I noticed though, is it seems the footage has more moire than in cdng. And that's a BIG concern, at least to me ! (When will blackmagic finally add an OLPF ?  ? ) Some people talked about the fact that BRAW acted like some kind of low pass filter (just like the PRORES did on the original bmpcc). But it seems to be the opposite. And the superman video Emmanuel linked tends to confirm my first impressions. This only could make me go back to firmware 6.1...

No worries man, wait to see a fair comparative test with lossy CinemaDNG 3:1, even though, I already guess the result and/or use slimraw to cut and end straight to 60% of bytes or increase equivalently the minutes length -- here's the table from where you/we can start to calculate ; -)

https://www.bmpcc4k.tech/

 

[amanieux]

3 minutes ago, Emanuel said:

LOL Good one! : -) I loved that one! Now we're talking! : -)

sorry i am not a photographer i am a computer scientist, my job is to write algorithms were "1" are always visually 1 and "0" are always visually 0 no matter the angle you look at it

 

[deezid]

4 hours ago, amanieux said:

what i don't get is that blackmagic could have minimized this BRAWgate but just adding a BRAW 1:1 consisting only of the uncompressed raw data for users who want maximum quality

Compression isn't even the issue here. Was using 4:1 cDNG all the time with fantastic results while Braw at Q0 still smudges texture, fine details, creates fringing and color bleeding issues as well as contrast halos around edges. 

It's just an internal processing issue and I really wish BMD could add a low or no internal processing option.

[kye]

Interesting discussion, but we need to be careful we don't deviate from what actually matters, which is how the image looks to people.

@amanieux is correct that there is lossless and lossy, but there is no real 'visually lossless' category, unless they saved space by removing the metadata or something, but that's basically pointless.

It's more accurate to talk about how much visual loss is caused by how much compression.  For example, mp3s are very highly compressed (down to single digit percentages) but the perceived sound quality remains a lot higher than the file sizes because they're very smart about what information they're removing, and have chosen to remove the things that humans are least sensitive to.

In visual terms there are equivalents to this and certain changes do a lot more perceived 'damage' to an image than others.  For example, if you took a video signal and made every pixel 2% brighter then we basically wouldn't notice and no-one would complain.  But if you made every pixel 2% brighter, but only on every second frame, it would flicker like mad and would be a total shit-show, despite the video quality actually having half as much total error.  
Obviously this is a ridiculous example, but when we compress video we are essentially doing two things, one is that we are choosing how much total deviation there will be (all else being equal, more compression = more deviation from the source material) and we are choosing where and how that deviation will be allocated, both in the frame and across frames.  When you heavily compress an image you often find horrific blocking artefacts in plain shadow areas, and also on flat surfaces next to edges.  This is due to how the image is compressed and which algorithms are used to do so.  It's less obvious today since the compression in JPG and MPG has kind of taken over, but those of us who recall comparing images from a GIF file that only had a small number of colours but could do flat surfaces and edges perfectly with a JPG image that could do many more colours but flat surfaces and edges abysmally will know what I mean.

It's kind of like when we talk about ISO performance of a new camera - one reviewer says "ISO 1000 is the limit" and the next person says "ISO 6400 is totally usable" and we're really none the wiser because all we know is that they have different tolerances for noise in their images.

In video we do have some standard measurements, like Signal-to-noise, but unfortunately that's difficult to calculate, and due to perception not being purely mathematical it's also not a reliable predictor of how good something looks.

In a sense, what we should have is a standard test of what percentage of people could tell the difference between the source and a compressed version over a range of delays between the images.  That would give us something like "compression example 1 was visibly different to 80% of people over a 1 second gap and only 30% of people over a 40s gap, whereas compression example 2 was visibly different to 60% of people over a 1 second gap and only 10% of people over a 30s gap" and that would be useful when compared with other things like file sizes etc.  Unfortunately, I don't know about such a standard test, and even if there is, no-one seems to be doing it.

[Emanuel]

5 hours ago, deezid said:

Compression isn't even the issue here. Was using 4:1 cDNG all the time with fantastic results while Braw at Q0 still smudges texture, fine details, creates fringing and color bleeding issues as well as contrast halos around edges. 

It's just an internal processing issue and I really wish BMD could add a low or no internal processing option.

What about the 6.1 firmware version + saving 63.3%?

source: http://www.cineticstudios.com/blog/2015/7/slimraw-an-easy-method-to-save-space-with-cinemadng-footage.html

 

According to my math you get 134 minutes of 4:1 into a 500GB SSD which is more space in disk than .braw 5:1 offers... Not bad if you have a capable machine to handle post, I guess, even though, slimraw promises a way faster workflow.

[marcuswolschon]

I mostly used to record raw for one specific purpose:  Denoising in post in scenes where the camera could not keep up with a very dark stage that contained well lit elements.

This was absolutely needed on the BMPCC with ISO1600 and is still needed on the BMPC4K when not blowing our the well lit scene elements.

For the simple reason that it would not compress the noise, so that NeatVideo (3, later 4) could do a great job on it.

[amanieux]

2 hours ago, Emanuel said:

What about the 6.1 firmware version + saving 63.3%?

 

 this 1:58 slimraw compression result is lossless and  the original was lossless cinemadng, correct ? 

[Emanuel]

7 hours ago, amanieux said:

 this 1:58 slimraw compression result is lossless and  the original was lossless cinemadng, correct ? 

Yes. No idea how it goes with 4:1, even though, the idea is to keep the original 4:1 quality. So, is there more space to save on disk? Maybe Mihail @cpc may drop a word here. I've called him on here but he seems to be offline so far though : -)

[cpc]

16 hours ago, amanieux said:

 this 1:58 slimraw compression result is lossless and  the original was lossless cinemadng, correct ? 

This is most likely uncompressed source to losslessly compressed output. It also looks like a rather old version of slimraw. But if you want to know more about the various types of compression in the dng format, here is an overview: http://www.slimraw.com/article-cdngmodes.html

(@Emanuel I am around, just not following the discussion closely )

[Emanuel]

14 hours ago, cpc said:

This is most likely uncompressed source to losslessly compressed output. It also looks like a rather old version of slimraw. But if you want to know more about the various types of compression in the dng format, here is an overview: http://www.slimraw.com/article-cdngmodes.html

(@Emanuel I am around, just not following the discussion closely )

Very useful indeed. Easy to understand as well. My hat, mate : ) I see you have new customer(s) here, I believe.

 

I am looking for three levels quality to know:

 

Quality A / QA:

- Green screen for VFX work;

 

Quality B / QB:

- Motion picture acquisition for intense grading work towards movie theater screening;

 

Quality C / QC:

- Casual shooting for further use as stock footage to fit any serious professional project later on wherever platform is (including big screen/broadcast, printing stills, etc).

 

I had found Q0, 5:1 and Q5 respectively the .braw answer to my needs.

What about slimraw?

 

You wrote: "When shooting a Blackmagic camera which allows for both lossless and lossy raw with the intent of passing the raw footage through any of the slimRAW lossy compression modes it is best to record lossless CinemaDNG in camera".

Does this mean should we avoid to record cDNG 4:1 or even 3:1 in-camera?

 

You also say there: "But if you are doing recompression (for example, when the source is Blackmagic lossless CinemaDNG) the resulting ratio will depend on the level of compression in the source files. For example, if the source is 1.5:1 losslessly compressed, and 3:1 is selected as target, then the result will be approximately 2:1 (or down 50% of the original size, for a total ratio of 1.5*2 = 3:1)."

From that table:

source: https://www.bmpcc4k.tech/

 

If we use your VBR HQ (for my QB usage above) let's take 3.5:1 as average compression, once cDNG compression by Blackmagic rounds 1.6:1, we'll end with about 80 minutes (more or less in the .braw range), correct?

How can we extend that without losing any quality towards my QB table trying to match 5:1 at .braw side at least?

 

Is it safe going with recompression?

What slimraw setting?

Would cDNG 4:1 or even 3:1 acquisition + VBR HQ be a possibility and safe enough to match my QB standard and goal?

[Emanuel]

PS as disclaimer:

I obviously intend to let clear that equivalent minutes length only comes later at post and under GBs form, of course. But, these new SSD of nowadays are true digital camera magazines as matter of fact, isn't it? ; -)

[cpc]

4 hours ago, Emanuel said:

I am looking for three levels quality to know:

 

Quality A / QA:

- Green screen for VFX work;

 

Quality B / QB:

- Motion picture acquisition for intense grading work towards movie theater screening;

 

Quality C / QC:

- Casual shooting for further use as stock footage to fit any serious professional project later on wherever platform is (including big screen/broadcast, printing stills, etc).

 

I had found Q0, 5:1 and Q5 respectively the .braw answer to my needs.

What about slimraw?

This is very resolution dependent, but assuming 4k, the corresponding settings would be: lossless,  5:1, and 7:1 / VBR LT.

 

Quote

You wrote: "When shooting a Blackmagic camera which allows for both lossless and lossy raw with the intent of passing the raw footage through any of the slimRAW lossy compression modes it is best to record lossless CinemaDNG in camera".

Does this mean should we avoid to record cDNG 4:1 or even 3:1 in-camera?

Only if you'd use slimraw in a lossy mode afterwards. It is generally better to avoid multiple generations of lossy compression, and there are a few significant differences in how in-camera dng lossy compression works in comparison to slimraw's lossy compression.

 

Quote

If we use your VBR HQ (for my QB usage above) let's take 3.5:1 as average compression, once cDNG compression by Blackmagic rounds 1.6:1, we'll end with about 80 minutes (more or less in the .braw range), correct?

Yes.

 

Quote

How can we extend that without losing any quality towards my QB table trying to match 5:1 at .braw side at least?

Well, 5:1 is matched by 5:1. The meaning of these ratios is that you get down to around 1/5 of the original data size, which is the same no matter what format you are going to use.

 

Quote

Is it safe going with recompression?

What slimraw setting?

Would cDNG 4:1 or even 3:1 acquisition + VBR HQ be a possibility and safe enough to match my QB standard and goal?

"Safety" is something only the user can judge. You are always losing something with lossy compression. It is "safe", in the sense that it is reliable, and it will work. VBR HQ will normally produce files between 4:1 and 3:1, but since it's constant quality/variable bit rate it depends somewhat on image complexity.

 

Now, it is important to note that it is probably not a good idea to swap a BRAW workflow for a DNG workflow, unless you need truly lossless files (for VFX work, for example). Even though a low compression lossy DNG file will very likely look better than an equally sized BRAW frame (because by (partially) debayering in BRAW you increase the data size, and then shrink it back down through compression, while there is no such initial step in DNG; remember: debayering triples your data size!), this quality loss is progressively less important with resolution going up. Competing with BRAW is certainly not a goal for slimraw. There are basically 4 types of slimraw users:

1) People shooting uncompressed DNG raw: Bolex D16, Sony FS series, Canon Magic Lantern raw, Panasonic Varicam LT, Ikonoskop, etc. The go-to compression mode for these users is the Lossless 10-bit log mode for 2K video, or one of the lossy modes for higher resolution video.

2) People shooting losslessly compressed DNG on an early BM camera (Pocket, original BMCC, Production 4K) or on a DJI camera: these users normally offload with one of the lossy modes to reduce their footprint (often 3:1 or VBR HQ for the Pocket and BMCC, and 4:1/5:1 for the 4K). Lossless 10-bit log is also popular with DJI cameras.

3) People doing DNG proxies for use in post with Resolve. They are usually using 7:1 compression and 2x downscale for a blazing fast entirely DNG based workflow in Resolve (relinking  in Resolve is a one-click affair and you can go back-and-forth between originals and proxies all the time during post).

4) People shooting BM cameras and recording 3:1 or 4:1 CDNG for longer recording times, who do their post in Premiere. They use slimraw to transcode back to lossless CinemaDNG in post and import the footage in Premiere.

Of course, there are other uses (like timelapses, or doing lossless-to-lossy on a more recent BM camera, if you are a quality freak (a few users are), slimraw will beat in-camera for the same output sizes, which is expected -- it doesn't have the limitations of doing processing in-camera), but these are less common. So yeah, if you don't need VFX, it is likely best to just stick to BRAW and don't complicate your life.

[Emanuel]

3 hours ago, cpc said:

This is very resolution dependent, but assuming 4k, the corresponding settings would be: lossless,  5:1, and 7:1 / VBR LT.

Yes, 4K: DCI and UHD. OK, so let's set up 5:1 compression as big screen requirement for 4K then. I've also arrived to similar conclusion as reported.

 

3 hours ago, cpc said:

Only if you'd use slimraw in a lossy mode afterwards. It is generally better to avoid multiple generations of lossy compression, and there are a few significant differences in how in-camera dng lossy compression works in comparison to slimraw's lossy compression.

Which means better to avoid lossy compression in-camera?

 

3 hours ago, cpc said:

Well, 5:1 is matched by 5:1. The meaning of these ratios is that you get down to around 1/5 of the original data size, which is the same no matter what format you are going to use.

I meant quality-wise.

.braw seems lower quality, I bet.

 

3 hours ago, cpc said:

"Safety" is something only the user can judge. You are always losing something with lossy compression. It is "safe", in the sense that it is reliable, and it will work. VBR HQ will normally produce files between 4:1 and 3:1, but since it's constant quality/variable bit rate it depends somewhat on image complexity.

 

Now, it is important to note that it is probably not a good idea to swap a BRAW workflow for a DNG workflow, unless you need truly lossless files (for VFX work, for example). Even though a low compression lossy DNG file will very likely look better than an equally sized BRAW frame (because by (partially) debayering in BRAW you increase the data size, and then shrink it back down through compression, while there is no such initial step in DNG; remember: debayering triples your data size!), this quality loss is progressively less important with resolution going up. Competing with BRAW is certainly not a goal for slimraw.

Competition is part of the game. Impossible to not compete if you offer something better.

 

3 hours ago, cpc said:

There are basically 4 types of slimraw users:

1) People shooting uncompressed DNG raw: Bolex D16, Sony FS series, Canon Magic Lantern raw, Panasonic Varicam LT, Ikonoskop, etc. The go-to compression mode for these users is the Lossless 10-bit log mode for 2K video, or one of the lossy modes for higher resolution video.

2) People shooting losslessly compressed DNG on an early BM camera (Pocket, original BMCC, Production 4K) or on a DJI camera: these users normally offload with one of the lossy modes to reduce their footprint (often 3:1 or VBR HQ for the Pocket and BMCC, and 4:1/5:1 for the 4K).

(...)

Does this mean the lower resolution the lower compression needed?

 

Quote

Lossless 10-bit log is also popular with DJI cameras.

Why not with Blackmagic cameras too?

 

3 hours ago, cpc said:

3) People doing DNG proxies for use in post with Resolve. They are usually using 7:1 compression and 2x downscale for a blazing fast entirely DNG based workflow in Resolve (relinking in Resolve is a one-click affair and you can go back-and-forth between originals and proxies all the time during post).

How to not see it as serious contender to the .braw workflow?! : )

 

3 hours ago, cpc said:

4) People shooting BM cameras and recording 3:1 or 4:1 CDNG for longer recording times, who do their post in Premiere. They use slimraw to transcode back to lossless CinemaDNG in post and import the footage in Premiere.

Won't this save disk space in the end? If so, how much will the ratio be?

 

3 hours ago, cpc said:

Of course, there are other uses (like timelapses, or doing lossless-to-lossy on a more recent BM camera, if you are a quality freak (a few users are), slimraw will beat in-camera for the same output sizes, which is expected -- it doesn't have the limitations of doing processing in-camera), but these are less common. So yeah, if you don't need VFX, it is likely best to just stick to BRAW and don't complicate your life.

LOL I guess there's a quality freak inside each P4K owner... ; )

 

In conclusion, what's the best method to save bytes as highest quality as possible other than VFX?

Lossless cDNG in-camera acquisition + Lossy 5:1 as for instance? Or some other compression ratio? -- What else then?

4:1 or 3:1 cDNG (any of both obviously lossy modes) in-camera recording + slimraw later on towards to archive / post? -- If so, what setting route? Lossless (slimraw)? What additional compression ratio?

Let's put big screen and intense color correcting / grading without the need of VFX as only paradigm now.

[cpc]

19 hours ago, Emanuel said:

Which means better to avoid lossy compression in-camera?

Only if you will be doing more lossy compression on the same video down the line, and the methods used in the different compression passes differ in some significant way. If you are going to use the same method (only with different amounts of quantization), it doesn't matter much. So if you'd be doing compression after acquisition with, say, slimraw, there are enough differences between lossy slimraw and lossy in-camera to warrant doing lossless in-camera.

19 hours ago, Emanuel said:

I meant quality-wise.

.braw seems lower quality, I bet.

Well, it is normal. Not only BRAW needs to happen in-camera which imposes some limits (power, memory, real-time, etc), but it is likely hindered by its attempt to avoid Bayer level compression (possibly due to the patent thing). On the other hand, denoising (which often goes together with debayering) does have advantages when done before very high compression.

 

Quote

Does this mean the lower resolution the lower compression needed?

More precisely, lower resolution images can withstand less compression abuse. It should be fairly intuitive: if you have a fixed delivery resolution, let's say 2K, and you arrive at this delivery resolution from a 2K image, you can't afford messing with the original image much. But if you deliver to 2K from a 4K source, you can surely afford doing more compression to the 4K image.

 

19 hours ago, Emanuel said:

Why not with Blackmagic cameras too?

BM raw is already tonally remapped through a log curve. The 10-bit log mode in slimraw is only intended for linear raw.

 

19 hours ago, Emanuel said:

Won't this save disk space in the end? If so, how much will the ratio be?

No. Size will always go up when transcoding from lossy back to the lossless scheme: this works by decompressing from lossy to uncompressed, then doing lossless compression on the decomrpessed image; you can't do the lossless pass straight on top of the original lossy raw, it doesn't work like this. So going this route only makes sense when people need to maximize recording times (and shoot lossy), but still want to use Premiere in post.

 

20 hours ago, Emanuel said:

In conclusion, what's the best method to save bytes as highest quality as possible other than VFX?

Lossless cDNG in-camera acquisition + Lossy 5:1 as for instance? Or some other compression ratio? -- What else then?

4:1 or 3:1 cDNG (any of both obviously lossy modes) in-camera recording + slimraw later on towards to archive / post? -- If so, what setting route? Lossless (slimraw)? What additional compression ratio?

Let's put big screen and intense color correcting / grading without the need of VFX as only paradigm now.

If you insist on using DNG, you'll get best quality per size from shooting lossless in-camera, then going through any of the lossy modes in slimraw: which one depends entirely on what target data size you are after. I honestly wouldn't bother doing it for a camera that has in-camera lossy DNG, unless I really, really wanted to shrink down to 5:1 or more.

[Emanuel]

1 hour ago, cpc said:

Only if you will be doing more lossy compression on the same video down the line, and the methods used in the different compression passes differ in some significant way. If you are going to use the same method (only with different amounts of quantization), it doesn't matter much. So if you'd be doing compression after acquisition with, say, slimraw, there are enough differences between lossy slimraw and lossy in-camera to warrant doing lossless in-camera.

Well, it is normal. Not only BRAW needs to happen in-camera which imposes some limits (power, memory, real-time, etc), but it is likely hindered by its attempt to avoid Bayer level compression (possibly due to the patent thing). On the other hand, denoising (which often goes together with debayering) does have advantages when done before very high compression.

Right. That's also where I believe cDNG coupled to slimraw will shine over braw at my first bet.

 

1 hour ago, cpc said:

More precisely, lower resolution images can withstand less compression abuse. It should be fairly intuitive: if you have a fixed delivery resolution, let's say 2K, and you arrive at this delivery resolution from a 2K image, you can't afford messing with the original image much. But if you deliver to 2K from a 4K source, you can surely afford doing more compression to the 4K image.

Correct. Reason why we can have less where there's more, not vice versa. People always call for '1080p enough' mantra without clue what they're asking for ; )

 

1 hour ago, cpc said:

(...) Size will always go up when transcoding from lossy back to the lossless scheme: this works by decompressing from lossy to uncompressed, then doing lossless compression on the decomrpessed image; you can't do the lossless pass straight on top of the original lossy raw, it doesn't work like this. So going this route only makes sense when people need to maximize recording times (and shoot lossy), but still want to use Premiere in post.

 

If you insist on using DNG, you'll get best quality per size from shooting lossless in-camera, then going through any of the lossy modes in slimraw: which one depends entirely on what target data size you are after. I honestly wouldn't bother doing it for a camera that has in-camera lossy DNG, unless I really, really wanted to shrink down to 5:1 or more.

That's the whole point : ) P4K doesn't shoot lossy cDNG (nor lossless) anymore in any way other than as going back to 6.1 firmware version.

In such case, is slimraw able to match braw file sizes as well the same amount of minutes length as for instance for 4K DCI 24fps 5:1 compression around the 110-120 minutes range per 500GB?

Quality-wise, enough for movie theater screening with intense color correction / grading work even though without VFX needs?

[helium]

On 3/12/2019 at 2:29 PM, deezid said:

With these strong amounts of spatial noise reduction creating all kinds of detail smudging, color bleeding, low frequency texture removal etc as well as edge enhancing creating halos and fringing - nope.

Are you claiming that you can detect these defects under normal viewing conditions or just that they're visible zoomed in?  Would you, for example, bet the house on being able to tell difference in a blind test, without being able to move your chair or hit the zoom key?  If the answer is yes, please link to full rez examples, so the rest of us can test our own eyesight under the usual viewing conditions.

If that sounds like I'm being over-generous with your time, you've repeated these same claims on several discussion sites, so surely you must have examples on hand?

[cpc]

22 hours ago, Emanuel said:

In such case, is slimraw able to match braw file sizes as well the same amount of minutes length as for instance for 4K DCI 24fps 5:1 compression around the 110-120 minutes range per 500GB?

Quality-wise, enough for movie theater screening with intense color correction / grading work even though without VFX needs?

Yes, a couple of hours of 4K at 5:1 should be somewhere under 500GB.

I usually recommend 5:1 for oversampled delivery only (i.e. when shooting 4K or higher, but going for a 2K DCP). I know some users routinely use 5:1 for 4K material and are happy with it, but I am a bit conservative about this. I'd imagine most indie work ends up with a 2K DCP anyway (well, at least anything I've shot that ended in a theater has always been 2K).

[Emanuel]

9 minutes ago, cpc said:

Yes, a couple of hours of 4K at 5:1 should be somewhere under 500GB.

I usually recommend 5:1 for oversampled delivery only (i.e. when shooting 4K or higher, but going for a 2K DCP). I know some users routinely use 5:1 for 4K material and are happy with it, but I am a bit conservative about this. I'd imagine most indie work ends up with a 2K DCP anyway (well, at least anything I've shot that ended in a theater has always been 2K).

What maximum compression ratio would you recommend in order to a 4K DCP with no need of VFX?