SHOULD YOU USE Rec709-A ? - Explained by a Colorist
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- čas přidán 1. 07. 2024
- Bonjour everyone !!
Rec709-A is used like the magic solution against your natural gamma shift, but it has some cons.
SOURCES :
ITU BT1886 : www.itu.int/dms_pubrec/itu-r/...
ITU BT709 : www.itu.int/dms_pubrec/itu-r/...
Article about Rec709-A behavior : ff.de/rec-709-a-exposed-navig...
Todd Dominey's video about Gamma shift on Macs : • Why Are QuickTime Vide...
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Time code:
0:00 Intro
0:38 What is Rec709 ?
1:41 What is a gamma ?
2:51 Why is there a gamma shift on Mac ?
4:38 Should you use Rec709-A ?
8:36 Outro - Krátké a kreslené filmy
The underlying issue is that Colorsync on a Mac does it's profile processing on the fly and Apple has ( to make a long explanation short ) a different gamma from the camera capture that it uses for the display function in your file. Apple assumes that a cameras capture will be the equivalent gamma of approx 1.96 and all other computers etc. have the math variable at 2.2 for the display function when writing to the card.
So when played back on a Mac it will have the correct gamma that you assign to it for a display function for your monitor but when it does the inversion on the fly for your monitor it uses the incorrect math from the camera and applies it to the function.
Warning technical data ahead.
Typical math with gamma 2.2
Suppose we have a camera that uses a gamma value of 2.2 for encoding (γ = 2.2).
1. Gamma Encoding (Camera):
• Let's say the camera captures a pixel with an original linear light value of V_in = 0.5.
• The gamma encoding operation is: V_out = V_in^γ = 0.5^2.2 ≈ 0.2176
• So, the camera encodes this pixel with a value of approximately 0.2176.
Then in the display gamma decoding ( for your monitor )
• Now, we want to correctly display this encoded pixel value on a monitor. We need to perform the inverse operation.
• The decoding equation is: V_out = V_in^(1/γ) = 0.2176^(1/2.2) ≈ 0.4999
The monitor will display this pixel with a value of approximately 0.4999 ( which is the .5 linear we started with )
This process ensures that the image is correctly displayed, compensating for the gamma encoding applied by the camera. This correction is crucial for the image to appear visually accurate to human observers.
Now if Apple uses gamma 1.96 for the gamma encoding to a file as it does on the fly whenever a file is going through Apple colorsync.
The display encoding math will return a different result - the V_out = V_in^(1/γ) = 0.2176^(1/2.2) ≈ 0.4999
in this equation using 2.2 we get the 0.2176 but using 1.96 we get 0.2570^ (1/2.2 ) = 0.5392
The difference being that the final gamma curve is slightly higher using 1.96
and the difference between 0.4999 ( using 1.96 ) and 0.5392 ( using 2.2 ) from the camera gamma,
the footage appears brighter at the display function.
But I think That Frenchie's opinion is correct - ignore it or bake it in.
If you bake in the rec709-a hack - it will have a distinct effect on PCs and other players that are not Macs.
I believe that Apple will eventually fix this problem in the future, and if they do all the Rec709-a baked in file out there will be wrong.
Best to ignore and make sure you have a calibrated display with a proper break out box that bypasses the Operating system and use that for all decisions.
Exactly, thank you for the comment, love your explanation as it adds more info to the video !
Warning technical data ahead? No need to warn us, mate. It is literally what the girl should have included in her vid, instead of stating the obvious... Content creators should stop trying to dumb down everything for the masses. Give us the facts. The hard data. Then the channel will be useful for people willing to learn. Normies will not make the effort anyway.
Great video Frenchie! Through explanation, I’ll be sending anyone with questions here. Thanks! 😁👍
REC709-A has worked for me and it seems to have a constant delivery for CZcams. I will experiment more...Thanks Frenchie !
Sure, this video is to help you guys to be more aware about how Rec709-A works and to understand better what's under the hood to make the best decisions possible for your comfort and your workflow :)
frenchie, this has been a problem I have had for days and I didn't know how to solve it. Today I was surfing youtube and suddenly I came across your video and you just helped me like you have no idea. thank you very much for sharing this information. keep uploading tutorials like this and you will go a long way.
I am happy my video was helpful to you ! 😊
Thank you for your knowledge about gamma selection. I make sure my output is what the client requests, avoiding any confusion down the line when delivering your product.
Brilliant!
I agree, this is also the solution I prefer as I am sure that there will no major issue with my export later in the process :)
Here's what I've experienced myself and what has worked for me:
The problem is the Apple's ColorSync and how Apple devices display the gamma and saturation of the colors.
If you are just grading web content on a Mac and don't have an IO device like BM Ultrastudio, you should have "Use Mac display color profiles for viewers" always checked in Resolve. This will make your viewer in Resolve match Apple's ColorSync. Your output color space can still be set to Rec709 gamma 2.4. The 1-2-1 tagged export will look the same on QuickTime player as it looks in Resolve, so no need for Rec709-A even in preview purposes :) However there will be a gamma shift when you upload that same file to CZcams, Vimeo etc.
When I grade on a Mac in Rec709 gamma 2.4 environment I do this: After the grade is finished, for the final export I'll put a cst node on timeline level going from gamma 2.4 to gamma 2.2 for content showed mostly on mobile devices, and for content viewed mostly on desktop, from gamma 2.4 to Rec709-A. Then leave the color space/gamma tags to "same as timeline" on the delivery page, so the file will be tagged 1-2-1. The timeline level cst node will make the image darker but it'll compensate for the gamma shift, and when uploading to the web the gamma will shift back to the original. For me this gets consistent and pretty close results and you can still grade the footage in gamma 2.4 setting.
Also from my experience, grading in Rec709 gamma 2.2 environment (with display calibrated to gamma 2.2) works if you are on a Windows, but after the exported file has been uploaded to CZcams etc, it will still have a slight loss in contrast/saturation when viewed on a Mac. And vice versa the footage graded/viewed on a Mac will look a bit darker when viewed on a Windows device. So it's basically impossible to make the same file look identical on both systems. You just have to decide yourself which one you want to prioritize. Just my two cents :)
I agree !
The answer with this whole gamma shift problem is "pick your battle" :)
That was helpful, thank you. :)
Understanding this problem is very much like chasing rabbits down rabbit holes in the bottom of a dark coal mine, with a box of matches for illumination.
My understanding of rec.709-a in resolve was that it was simply a tag, not a grade. So you output rec.709 gamma 2.4 with a tag of rec.709-a so that QuickTime recognises the output as rec.709 gamma 2.4. And other systems and applications would then just ignore that tag.
It seems to me based on your tutorial that we ought to be delivering bt-1886 for broadcast, and distribution when rec.709 gamma 2.4 is requested or when destined for tv broadcast. Because that sidesteps the issue of the gamma curve of rec.709 being “undefined” or misinterpreted, yet meets the assumed broadcast standard of rec.709 at gamma 2.4.
Genius!
OOOH I've wondered this since I have a Mac and 709a so far has given me good consistent output. Can't wait to watch this.
Same for me!
It works i have tried it thanks Frenchie i only apply that at the timeline level colour management when exporting i left it at timeline option it works for me no darker or washedout image and am haopy with it
I edit on a Mac and deliver in color space tag P3-DCI and gamma sRGB and my colors are consistent everywhere even without checking “use Mac display” in settings. The only time I change it is when delivering for TV since rec709 is the broadcast requirement.
Merci cher Frencie! Vote for democracy next weekend ! Vive la France! ... and I like the nice warm light split setup
I have to used Rec.709-A as my OutPut color space every time (in my project settings). otherwise my final render and the CZcams video looks washed, all my color grading is gone. I don't understand why. So I would like to try rec709 gamma 2.2 but this is the problem. This is one of my challenges stuff to learn. I'm using a Macbook.
Very good video… rec709A g2.2 CST node best used in pre grading then disable mode and export to rec709 g2.4
Super Chloé, merci ! Il y a plein de youtubeurs qui suggèrent l'utilisation du Rec709-A mais je préfère l'avis de quelqu'un dont l' étalonnage est le métier ! 😊👍
Merci ! Oui. tout le monde sort Rec709-A comme l'arme magique pour contrer le gamma shift mais en termes de deliverables, cela peut engendrer des problèmes dans les exports, ce qui peut vraiment embêter le client
@@frenchiecolorgrading absolument, encore merci pour cette mise au point ☺️
Brilliant!
@@frenchiecolorgrading Bravo pour ta vidéo. Je vais me faire l'avocat du diable du CZcams game de l'étalonnage, hehe. Les trois quarts des vidéos que je vois sont faites par des gens qui ne connaissent pas vraiment notre métier, qui n'ont pas de I/O box. Pour moi, cela signifie juste : c'est top, hein, faire de l'étalonnage sur un moniteur où tu n'as aucune certitude du rendu. Certains te diront qu'il y a le clean feed, mais après avoir fait le test encore récemment, il y a des différences et des incertitudes dans le clean feed. Donc, forcément, pour eux, le gamma shift n'est pas la priorité.
En revanche, comme tu l'as très bien expliqué (encore bravo), la différence se trouve dans les tags. C'est pourquoi, notamment pour les uploads en ligne, le mieux est de changer les tags de l'export. Faire un export en gamma 2.2 avec un tag 709-A est une possibilité envisageable (sinon vous allez avoir un différentiel dû à la compression de la plateforme). Ah, et dernier point : n'utilisez pas VLC. Ok, le logiciel lit tout, mais il bypass les informations colorimétriques.
Curious! what I do is grade 2.4 709 etc, but on timeline made a 709a cst, and also add rec709a on gamut tag. Seems to export properly that way for me but the primary reasoning behind it being the 1-1-1 tag carrying through
As for calibration Mac display custom calibration is good ?
What if I am using Benq monitor as my secondary display and Macbook pro as my primary display. where My reference monitor is BenQ PD2700U.
If you select the “use mac” in davinci preferences does it matter what iMac monitor profile you are using?
Nice.
What about automatically tagging Rec.709 as Rec.709-A in the general preferences as seen at @8:00 ? Will that stuff things up?
Thanks for this. One question : While grading in Resolve, I use my M1 macbook as viewer for video clean feed. What should the display settings within Mac OS system preferences be set at?
Especially if delivery is to be made to different platforms like TV, internet, cinema? There are many in-built display presets which make it confusing.
If your Macbook is your viewer for video clean feed then you'll have to calibrate it.
The calibrator will create an icc profile and overwrite the default you have :)
This is exatcly why I grade in HDR first and trim down to SDR using Dolby Vision. Or I export as Dolby Vision 8.4 which is interpreted as SDR correctly when the destination doesn't support HDR/DV.
PQ Gamma aka ST.2084 doesn't suffer from any of this nonsense
what you monitor referent ?
Not taboo for me: I'm using a PC (but with a crappy monitor which isn't even calibrated 😭)
Ta vidéo est top, mais il y a un un petit manque : 🥔🐇😁
OMG THANK YOU FRENCHIE !!!
Seeing your comment the other day, I think it was time I make a video about it !!! :p
@@frenchiecolorgrading This is SUUUUPER helpful!
I have some more questions! if i work on a gamma 2.2 timeline and render it out, there will still be a gamma shift right? I saw the other video of you
explaining that when use gamma 2.4 > for viewing use compensation lut before render.
but if i work on 2.2, is there a compensation lut for it as well?
another question: you use calbrite right? i assume i can just set the calibration to either 2.2 or 2.4 right? ahaha
i was gonna hired a monitor calibrator guy who uses a spyder i guess thats not accurate enough.
thank you so much Frenchie ! you are the best !
best regards from Bangkok
peng
@@PengTn The compensation lut is only for preview purposes, not for delivery :)
If you want to use it, it will give you a Rec709 gamma2.4 compensation so if you are set in gamma 2.2, stay in gamma2.2 without any compensation, you won't have that much shift :)
With Calibrite you can set your calibration in 2.2 and 2.4 yes :)
I also only advice on tools that I know. As I've never used Spyder, I don't know if it's good or bad so maybe make your researches if you hesitate on having a calibration with a Spyder :)
@@frenchiecolorgrading Thank you Frenchie @ Gamma 2.2 it is ! if little to no shift, ill give it a try ! thank you for putting your time to make this video for me and everyone ! we re forever grateful !! 10000% you have my support ! thank you !!
I work with a Mac mini on a BenQ monitor, should I enable 'use Mac display color profile'? Thanks!
Use mac display color profile is basically telling Resolve to use the system color profile without Resolve going in between.
On this I would suggest to have it on as you have still color utility working in the background even with a mac mini.
I strongly suggest though to have a grading monitor connected via an I/O device to control your grade if you can, this is the best and safest bet to have correct colors :)
I wish you showed an example color grading it in a Mac but this was very helpful. Thank you!
So, as long as I'm using an external monitor calibrated to 2.2, I don't even need to concern myself with 709-A. Am I understanding that correctly?
Exactly, trust your monitor
The mac is doing its own thing by itself, it is a too free spirit to be reliable 😀
Gamma es Muy importante !
It is !!!!
This is one of the best explanations of this mess, but I still do not understand it. 😃
Auto colour!!! 😄😄
Ahahahahah, the most awaited video 😂😂😂😂
The Solution : Work on Windows - no more gamma shift issues haha
@@FilmOneShot haha, in starting to feel this way myself
gamma is absolutely not contrast lmao
It is, it's representative of the curve on our monitor. Log to 709 is just a contrast curve but expressed mathematically.
frenchie, this has been a problem I have had for days and I didn't know how to solve it. Today I was surfing youtube and suddenly I came across your video and you just helped me like you have no idea. thank you very much for sharing this information. keep uploading tutorials like this and you will go a long way.
Hi, I watch your channel and I really like it. Could you make a video about color grading for movies shot with an iPhone, for example, the 13 PRO model? Without using LOG coding.
There is no such video and there are many users with similar phones.
I’d love to see this too!
Why not, this is great idea :)