ycbcr709 vs RGB709

[Hector Berrebi]

hi Aaron

if you are referring to the new feature in MC5 when opening a new project or changing a project in the format tab, then the difference would be in handling formats natively shot in RGB/YCbCr color spaces for finishing and color work. avid’s YCbCr is 4:2:2 color space meaning it is suitable for formats shot 4:2:2 (most pro HD formats such as dvcprohd, xdcam 422, most prores files,SR captures, and more). in this sampling method, half of the color information is lost in camera. sounds hard… its not that bad 🙂 broadcast requirements are 4:2:2, our eyes hardly notice the differences, and most of the viewing equipment (TVs and projectors) wont be that subtle anyway. if you generally work with 4:2:2 material, in 4:2:2 space you should be happy

RGB is a color space in which each primary color is individual captured with its luminance values included (unlike ycbcr where luma and chroma are sampled separately). some cameras shoot either in RGB or in 4:4:4 sampling, both keeping all color information (RED, ALEXA – both as raw and as prores 4×4, uncompressed HD coming from dual link hd-sdi cameras, some variation of SR and more)

when working with these formats and finishing on same AVID you would choose RGB
for higher fidelity and better response in color work and better looking video.
consider though, that hardware requirements are strict and quite high, from your drives’ speed to your video card and monitor.

when working with RGB materials for an end result which is YCbCr you can also select RGB, to maintain full color space until final export or output

this will only work for 1080. SD and 720 is ycbcr

its nice that AVID added this option to MC.
i’ve used it on RED material and was pleased with results, which ended up being ycbcr.

one thing though… it is a bit confusing that its called RGB 709. unless i’m terribly wrong its a mistake on Avid’s side. it should be called 4:4:4, or just RGB

RGB and 709 are different color spaces, where black and white have slightly different values (clipped in 709)

as 709 is a broadcast recommendation, and there is no need currently (and in coming years) for 4:4:4 broadcast material, the the options should be RGB (for film and potentially web) and 709 (which would mean Ycbcr 4:2:2 hd)

is there any use for YCbCr 709 4:4:4 option?

would be glad to be corrected on this one…

if you refer to export and import settings btw, then its a different matter, more dealing with white and black clipping

hope this helps

hector

Hector Berrebi
Schibber Group
prePost Consulting

[Avi Lev]

If I understand you right I should set the Color Space on YRbCr709 in case I’m editing HDV 1080i material

[Hector Berrebi]

[Avi Maximoose] “If I understand you right I should set the Color Space on YRbCr709 in case I’m editing HDV 1080i material”

yes

you should almost always set it that way.

the only times you might need to set to RGB is when finishing material that was recorded that way (and kept that way) on your system. RED files for example. to be done properly, this will be hardware demanding.

and even then, in most cases, it would be an overkill

Hector Berrebi
Schibber Group
prePost Consulting

[Daniel Huber]

“one thing though… it is a bit confusing that its called RGB 709. unless i’m terribly wrong its a mistake on Avid’s side. it should be called 4:4:4, or just RGB ”

This is not a mistake, it is due to the fact the avid will always output at rec709.

[Aynsley Baldwin]

With regard to the original post and this comment: “one thing though… it is a bit confusing that its called RGB 709. unless i’m terribly wrong its a mistake on Avid’s side. it should be called 4:4:4, or just RGB ”

I’ve always found the topic of RGB vs Rec709 vs YCbCr super confusing. Since this thread was created, Media Composer at least has changed the language in some parts of the software and made it a bit more intuitive. But one thing that’s also helped me decode some of the confusion is learning more about what all these and related terms actually mean. For those of you out there who have been equally confused, here’s a bit of a tangent… and please, folks, correct me if I’m wrong here.

As I understand it, the specific term “RGB” does not refer to a colour space, it refers to a colour model. That is to say it refers to a method of quantizing colour information that assigns a value to each of the R, G, and B channels. Each of these three values account for luminance. There are many colour spaces which use the RGB model, including sRGB, Adobe RGB and ACES as examples.

By comparison, as Hector explained, YCbCr is a colour space that uses a model which assigns one value for luminance that is separate from two chrominance values.

The origin of the term “Rec709” refers to a “Recommendation” made by the International Telecommunication Union on the “Parameter values for the HDTV standards for production and international programme exchange.” This is a list of allowable specifications for HD broadcast which include frame size, frequency, frame rate, colour, etc. It is important to note that Recommendation ITU-R BT.709 specifies values for encoding colour in either an RGB channel configuration, OR YCbCr, and 8 bit and 10 bit options for each.

As far as I understand it, this is why you can have RGB 709 and YCbCr 709.

The things that have confused me endlessly over the years are:

• RGB often seems to be used to mean sRGB, though there is an important difference between the two terms. sRGB is a colour space with a specific gamut and white and black points associated with it, while the simple term “RGB” refers more generally to a way we organize colour information. It’s like saying “software” when you mean “Media Composer.” Maybe it’s just me, but it seems like as a result the actual meaning of RGB when it IS used correctly is often misunderstood.

• YUV is often used to mean YCbCr. YCbCr, as I understand it, is a kind of derivation from YUV, but again, not the same. Even the latest version of Adobe Media Encoder refers to it YUV instead of YCbCr. Arg.

• My perception is that Rec. 709 is often thought to be a colour space, which technically speaking it is not. The HDTV broadcasting standard known as Rec. 709 includes specifications for allowable colour values and luminance values, and those are often referred to as “Rec. 709” (especially in Media Composer), clouding the fact that Rec. 709 actually represents a much wider array of specifications.

• Given that my introduction to all of these things was pretty much through early Media Composer import and export settings, my sense was always that sRGB (or at least what I now understand to be sRGB) and Rec. 709 were two entities equal in form, opposing in content. Not true! The sRGB colour space uses the primary colour values dictated by ITU-R BT.709 (Rec. 709) broadcasting standard. The white and black points, however, in sRGB colour space are outside those dictated by Rec. 709, and this was what Media Composer was always asking you to choose between on import and export. sRGB white and black points have digital values of 0 & 255, whereas Rec. 709 specifies values of 16 and 235. The new language used in the import settings, “do not modify, keep as legal” and “scale from full to legal” (legal implying Rec. 709 broadcast standard) is much clearer, but still not ideal IMHO.

Getting back to Aaron’s original question, YCbCr colour spaces vs RGB model colour spaces come up as options when setting up a project. Whereas I believe the options in the import/export settings (formerly asking one to choose between “601/709” and “RGB” or sRGB as I believe it should have been named) refer only to how you want to affect the luminance range on a specific import or export.

[Daniel Huber]

Aynsley Baldwin, that is all correct information. One thing you have to keep in mind is Avid is not Adobe or FCP and this has nothing at all to do with colorspace like still images colorspace.

This is all about what a consumer TV in your home can handle. What is the colorspace of the device the footage will be viewed on in the end.
We add video “color space” for each time the industry changes. think RGB is a computer monitor, REC709 is your home TV, and now we have 2020 and beyond!

Avid just always assumed back in the day that you were going to output via a broadcast signal. 709 simply has to do with blacks and whites, or Y waveform (luminance) Avid always would output via 16-235 in the Y channel.

We asked you what type of footage you were bringing in so it could deal with the white and blacks levels correctly.