Thread: An easier way to grade log footage - Tutorial

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  1. #31  
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    I'd argue that the sky is actually cyan but it really doesn't matter. The pure color blue in rec709 or RGB colorspace can only exist at about 10IRE brightness. The only way for it to be brighter is to mix it with white or shift toward cyan or red. Arguing a camera's ability to reproduce a color that 99.99% of displays can't even display mathematically let alone physically is kind of pointless. Here is a simple ramp from white to pure blue, do you see magenta? I do but the vector scopes do not. It's simply impossible within rec709 or sRGB to have pure blue at a luminance level that would represent a mid day sky.

    Blue?.jpg
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  2. #32  
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    Quote Originally Posted by Howie Roll View Post
    I'd argue that the sky is actually cyan but it really doesn't matter. The pure color blue in rec709 or RGB colorspace can only exist at about 10IRE brightness. The only way for it to be brighter is to mix it with white or shift toward cyan or red. Arguing a camera's ability to reproduce a color that 99.99% of displays can't even display mathematically let alone physically is kind of pointless. Here is a simple ramp from white to pure blue, do you see magenta? I do but the vector scopes do not. It's simply impossible within rec709 or sRGB to have pure blue at a luminance level that would represent a mid day sky.

    Blue?.jpg
    POW! There it is.
    Our eyes lie to us all the time.
    Scopes don't.
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  3. #33  
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    After comparing an Alexa to an UMP46 I have to admit, though, that there are differences. The Alexa is holding a tad more color close to sensor saturation. Surprised? Check the price…
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  4. #34  
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    Quote Originally Posted by yoclay View Post
    It's defensive, aggressive and uncalled for.
    Defensive AND aggressive, wow I must have some skill to do both at the same time. Thanks for the compliment.
    I'll re-phrase to protect egos a little, "I think you're full of it". That's my opinion on what you've said. I'm entitled to share my opinion, right?

    That you have this as your signature is VERY ironic considering what you say and seem to like:

    If I wanted my films to look like the real world I'd buy a video camera.
    WHY AREN'T THE SKIES PURE BLUE AND ONE COLOR???!!!

    What? Hahahaha.

    Quote Originally Posted by Howie Roll View Post
    I'd argue that the sky is actually cyan but it really doesn't matter. The pure color blue in rec709 or RGB colorspace can only exist at about 10IRE brightness. The only way for it to be brighter is to mix it with white or shift toward cyan or red. Arguing a camera's ability to reproduce a color that 99.99% of displays can't even display mathematically let alone physically is kind of pointless. Here is a simple ramp from white to pure blue, do you see magenta? I do but the vector scopes do not. It's simply impossible within rec709 or sRGB to have pure blue at a luminance level that would represent a mid day sky.

    Blue?.jpg
    Yep, nice example. Or maybe the color science behind rec709 should be revisited?
    Last edited by Steven Abrams; 12-19-2017 at 05:54 PM.
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  5. #35  
    Senior Member shijan's Avatar
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    Quote Originally Posted by yoclay View Post
    Hi Shijan,
    Those are excellently balanced pictures. Some of the best I have seen.


    However, I am not sure that a color checker is the answer (I myself own 5 and prefer the SMPTE charts for skin tones).
    The reason is because you are shooting them in an ideal condition with even diffused and controlled lighting in a very limited contrast range.
    It is much more simple to match cameras from various manufacturer's under those conditions.
    The issue is that when charts are used in uneven lighting conditions, or when the subject is in very different light than the rest of the scene, the performances can be quite different.
    Skies react in an entirely different way than the reflective aspect of a chart. They are quite transmissive and the issues I am seeing have to do with color shifts over an extended contrast range.
    A color chart essentially functions well in the center of the triangular gamut, however what concerns me is on the edges of the triangular spectrum of the color space for any particular camera and how those are mapped in this case.

    When you refer to "the random shifts" which come with desaturation, I also don't think these colors are as easily recoverable as you state. I feel that I am having to "jump through too many hoops" to restore certain aspects of the color spectrum.

    I know that that all camera manufacturer's create input profiles for the intrepetation of their data. That is not in question.
    What I am asking is precisely that they revisit that input profile, because in my estimation there are too many issues there currently.
    No need to do separate ColorChecker sample for every shoot. Just do ColorChecker correction in normal light conditions and apply that node to any shoot done in different light conditions. This will work way better than factory input color correction profile.
    One more tip - do ColorChecker correction in wide gamut color space and Log curve. ColorChecker correction in Rec709 looks ugly.
    This is a custom made workflow with custom made "color science" i described many times in other threads.
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  6. #36  
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    Thanks for actually pointing at some images so that we can at least discuss what you’re seeing in a meaningful way.


    Quote Originally Posted by yoclay View Post
    Juan, has done a good job of illustrating by his 4 step transform process, that there is definitely some hoops to jump through.
    Quote Originally Posted by yoclay View Post
    His process clearly illustrates why I think BM needs to revisit it's "color science". That process he has shown, shouldn't be necessary.
    I believe you're mis-representing his excellent and easily understood videos.

    He first documented his process for working with LOG footage using Alexa and FS700. It’s the first posting in this thread and without a single reference to Blackmagic footage.

    https://www.youtube.com/watch?v=8qJ7i9b28Lo

    Then he explained how he uses the same process with Blackmagic DNG files here.

    https://www.youtube.com/watch?v=T31lBQymEPs

    Theres no extra steps or hoops or clear illustration of anything. Juan clearly explains his process of working with ANY high dynamic range LOG encoded footage and if I may paraphrase it...

    ...take footage, transform it into a LogC curve, grade. (The BMD version would be take footage, linarise it, transform it into a LogC curve, grade.)

    No hoops jumped. It's his same process for any camera.

    Quote Originally Posted by yoclay View Post
    This is likely because Arri uses a pseudo HDR technology for the highlight rolloff and retains approximately a 1.5 stop gradation/transition in it's highlight values.
    Seems to me that this has already been well addressed by the numerous equally cyan sky images posted form Arri’s own channel, and I think Howie’s illustrative post about the Blue ramp.

    You use of the phrase “pseudo HDR” technology is intriguing. What exactly is it are you referring too here ? You mean their curve as embodied by what Juan has already shown a preference for LogC ? Or their dual gain sensor architecture ? Where do you get the 1.5 stop figure from ?

    If I was to guess it seems to me you like the way the Alexa holds onto colour into the highlights for longer than other cameras can do ?

    Because this is what Howie’s blue ramp post so eloquently demonstrates. As you increase brightness, saturation decreases.

    Skies, funnily enough trend towards be overexposed in a lot of our work. We tend to want to expose for what's on the ground and in foreground, and it's usually what's dramatically important. So we tend to expose for that and let the background / sky, go a bit hot.

    Juan uses one of my images in his demonstration of his technique in his demonstration of his 4 step process. It’s a deliberately difficult shot from the launch footage of the Ursa Mini 4.6K, devised to demonstate exactly what we're talking about here, trying to maintain high dynamic range. When you have a shot that has the actual sun in shot, it's always a challenge. Without any fill light, whilst still trying to hold the most amount of DR, there is detail in both shadows and highlights. Now your issue is that the sky is cyan and how those highlights track, but as I think we’ve shown, that as exposure increases towards brighter, we will always struggle to hold colour. Many examples of this from Alexa have already been posted.

    I think you just prefer the way Alexa handles this particular issue. And they do handle it very well, no doubt. The do it better than BMD do. But it’s not infallible.

    They have the same cyan and magenta issues as you've already conceded.

    Maybe this article will resonate with you

    http://www.dvinfo.net/article/produc...in-common.html

    In my experience the very strong language you use doesn’t line up with how close Ursa is to Alexa in holding detail in highlights with the issue you raise.

    Even if we accept this is a small differences as you have already done, they really aren't as large as you infer with this language.

    Quote Originally Posted by yoclay
    skin tones that lack appropriate nuances
    overly present Cyan dominance in skies
    we have to jump through a lot of hoops in order to get something faintly normal
    Its as if certain zones were 12 or 14 bit and others were 8 bit within the same image !
    The image falls apart from a color point of view
    transitions are not smooth
    The color is thin and falls apart even from Raw
    But the images are actually quite dull
    It is a problem that issues from color depth


    Quote Originally Posted by yoclay
    I can spot a video shot outside on a BM camera from a mile away
    Here’s a bunch of screen shots. Only the dallies LUT from the show was applied, no real grading, no keys, no secondaries. CDL grading only on top of the show LUT. Tell me which ones are Alexa and which are Ursa.

    And here's a clip that has Alexa and Ursa intermixed. I invite you to call them out.

    https://www.youtube.com/watch?v=Ms8faxqWtKU


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  7. #37  
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    "I can spot a video shot outside on a BM camera from a mile away"


    What size monitor would you be using for that technique?
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  8. #38  
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    No problem guys, enjoy your cameras.
    If I wanted my films to look like the real world I'd buy a video camera.
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  9. #39  
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    No matter who is correct I feel people were indeed too aggressive or in a sense not professional. While this isn't a professional platform and even if someone is or isn't completely incorrect is besides the point, it's important to remain respectful and while yoclay's opinion may have been against the many and yes he took a while to show examples he remained respectful where as many of the comments made towards him were not something I would say in a face to face situation to someone, so I believe it's important to keep that in mind here also.

    It's hard to respond when people are throwing in unnecessary comments, it's easy to miss the point of your message. It's better in my experience to take in someones criticisms even if it seems incorrect to find out why they are saying it, being overly abrasive I found only shuts down the conversation.

    This is all just my point of view following this thread along. I can see where it may have frustrated being a follow on from another thread or previous experiences but half of the responses here aren't necessary.
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  10. #40  
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    If you're refering to my comment I'd just suggest that after reading paragraph after paragraph of combative rhetoric that runs contrary to common epxerience here - a simple short sentence is hardly aggessive.
    And as a business owner and team leader it's exacty the type of "lighten up" comment I would make to someone, directly, after a hyperbolic assertion.
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