Are dE and Gamma calculated the same way in HCFR and Calman V3 for a plasma? Thanks.

Jim

Anyone?

Anyone?It's an impossible question to answer because CalMan offers more than one dE calculation and HCFR and CalMan each offers more than one gamma formula.

In CalMAN V3 we offer DeltaE in 1976, 1994, 2000, UV and Max with an option to turn off luminance in 76 and 94, we also break out the 1994 components in to L, C and H. As for gamma formula we offer ITU/EBU, Power, Dynamic offset and Studio RGB with an option for Black Level Compensation. For gamma exponent you can select from 1.0 to 5.0 with the default at 2.2. We have documentation on all of the above about the how and why of each and how the options effect the formulas.

In CalMAN V3 we offer DeltaE in 1976, 1994, 2000, UV and Max with an option to turn off luminance in 76 and 94, we also break out the 1994 components in to L, C and H. As for gamma formula we offer ITU/EBU, Power, Dynamic offset and Studio RGB with an option for Black Level Compensation. For gamma exponent you can select from 1.0 to 5.0 with the default at 2.2. We have documentation on all of the above about the how and why of each and how the options effect the formulas.

I will be getting the i1pro and Calman next year when the wifey loosens the purse trings:o But until then I am trying to learn about DIY calibration. I already tried the whole sale ends soon, etc, etc. But no go.

Could you enlighten me, or point me to a good resource that discusses gamma. In particular I was wondering if there is a standard for gamma (like color temp....6500k)? Would that standard be 2.2? Also, what are the differences between shooting for a slightly lower gamma or higher gamma in terms of PQ characteristics? Thanks.

This is a good question, and one that deserves more complete treatment than it has previously received. The current standard for HD, Rec. 709, specifies a linear portion of the curve at very low levels then a more traditional transfer function from there. The degree to which non-linear encoding follows this recomendation varies greatly. That means that if you calibrate a set to match that transfer function, you may or may not get results that work well. This is just the beginning of what complicates the discussion. Each display has different characteristics with regard to its adjustability and gamma behavior. Few have controls that allow you to match the rec.709 response, and many are erratic in their effect, not even following a simple power curve. Now add different types of displays in different lighting conditions, and you have a very large number of variables.

Now consider how we describe gamma. You will see it discussed as a single number in most cases. This single number can have very different effects on different sets with different response curves. It cannot describe the relative response at any one point or any particular area of the curve. 2.2 or 2.5 might mean very different things on different sets depending on how the response curve actually behaves.

The bottom line...well, most calibrators shoot for something between 2.2 and 2.5, usually measured relative to a power curve. It is simply meaningless to argue about the numbers to any degree of precision, however, because the reality is that there are to many variables, it is not a curve easily described by one number, and we have to work with the limitations of each display. This is where the science gets mitigated by the judgement of the calibration specialist, i.e., you have to wing it...

This is a good question, and one that deserves more complete treatment than it has previously received. The current standard for HD, Rec. 709, specifies a linear portion of the curve at very low levels then a more traditional transfer function from there. The degree to which non-linear encoding follows this recomendation varies greatly. That means that if you calibrate a set to match that transfer function, you may or may not get results that work well. This is just the beginning of what complicates the discussion. Each display has different characteristics with regard to its adjustability and gamma behavior. Few have controls that allow you to match the rec.709 response, and many are erratic in their effect, not even following a simple power curve. Now add different types of displays in different lighting conditions, and you have a very large number of variables.

Now consider how we describe gamma. You will see it discussed as a single number in most cases. This single number can have very different effects on different sets with different response curves. It cannot describe the relative response at any one point or any particular area of the curve. 2.2 or 2.5 might mean very different things on different sets depending on how the response curve actually behaves.

The bottom line...well, most calibrators shoot for something between 2.2 and 2.5, usually measured relative to a power curve. It is simply meaningless to argue about the numbers to any degree of precision, however, because the reality is that there are to many variables, it is not a curve easily described by one number, and we have to work with the limitations of each display. This is where the science gets mitigated by the judgement of the calibration specialist, i.e., you have to wing it...

Interesting. So would you advocate using the good old eye sometimes to see what various gamma measurements mean for PQ? Also, if you shoot for 2.3 gamma, would it be wise to shoot for a constant gamma at 10% ire, 20% ire, 30% ire etc.? (I think it is ire anyway).

Thanks

I look at the curve and start by trying to get it to track as closely as I can. Then I consider what the display gives me. From there you have to judge what trade-offs are best for the situation. As always, start with the standards and the science, and when they can't be achieved or don't get you what you need, work with what you have.

Could you enlighten me, or point me to a good resource that discusses gamma. In particular I was wondering if there is a standard for gamma (like color temp....6500k)? Would that standard be 2.2? Also, what are the differences between shooting for a slightly lower gamma or higher gamma in terms of PQ characteristics? Thanks.
One resource that is often overlooked is the CalMAN trial. While you can't use it with a colorimeter or spectro, you can go through the extensive set of help files, including sections on gamma that are specific to CalMAN, as well as ones that are fairly general to calibration in general (How-To's). The help file also adapts to the user profile you select, so if you find it a bit spartan on the "basic" mode, then up the level to intermediate or advanced.

This is a good point. There is much to be learned about calibration and the underlying principles by just going through the CAlMAN help files.

Again, the thing to remember is that gamma is really not well described by a single numeric value. Learn to understand what the curves mean and how your particular display responds to brightness, contrast, gamma, backlight, and even gray scale controls.