How to Choose a Professional Display Monitor (Part Five): Understanding Delta and Charts

In Part One and Part Two we classified professional display monitors according to our need.

In Part Three and Part Four we looked at how manufacturers classify their monitors and why.

In this final part, we will get our hands dirty, and see how we can put all this information to good use. But first, let’s tackle Delta and Charts.

Eizo CG246

Understanding Manufacturer Reports and Graphs

I’m sure you’ve seen many movies where a prosecutor browbeats a witness with a ‘Yes or No’ question. The witness wants to clarify his or her answer, but the prosecutor demands a Yes or a No.

This is approximately how marketing and management executives question engineers. They don’t care which data or graphs tell the whole truth, only the ones which show the product in best light. It’s basic Sales 101. If you’re selling your services, you wouldn’t highlight your negatives, or would you?

Monitors are all about grey. Manufacturer charts are useful, but only to an extent.

First you need material. Here are links to five documents provided by their manufacturers:

Model Colors Adobe RGB sRGB/ Rec.709 NTSC Price*
Dell Ultrasharp U2410 1.07 billion 96% 100% n/a $422
NEC PA241W 1.07 billion 98.1% 100% 93.2% $1,099
Eizo ColorEdge CG246 1.07 billion 97% 100% n/a $2,459
HP Dreamcolor LP2480X 1.07 billion 100% 100% 133% $2,217
Dolby PRM-4200** 1.07 billion n/a 100% 100% $30,000

*Prices are as per Amazon, February 20th, 2013. Dolby price is not confirmed, please contact manufacturer directly.**Dolby PRM-4200 also supports 100% DCI P3. It is the only monitor that is 42″ . The others are all 24″ monitors.

These monitors are factory calibrated, and might come with reports for each unit. But you only get it after you purchase your display monitor. If you’re an experienced colorist or video signal engineer, you can make mincemeat of the specifications any manufacturer provides. But what if you’re starting out?

Colors and Color Bit Depth

You might find manufacturers referring to 12-bit or 10-bit or 16-bit ‘processing’, but that’s not the monitor’s bit depth. You might find 12-bit or 16-bit or 10-bit ‘LUTs’, ‘Dithering’, etc., but that’s not the monitor’s bit depth. So, what is the monitor’s bit depth?

Take the total number of colors, and use the simple formula I explained in What is Color Bit Depth? You should get 10-bits for all of the monitors in our list. An 8-bit monitor can show only 16.7 million colors.

If a manufacturer is sketchy about this, use this method as a rule of thumb.

Color Space and Gamut

You can see from the values NEC provides that even 98% of Adobe RGB isn’t good enough for true 100% NTSC (SMPTE C). This is why NTSC capable professional display monitors are expensive, even today.

On the other hand, Rec. 709 is child’s play. The average high-end consumer monitor meets this requirement. The cheaper ones don’t, mind you. Most mobile device displays don’t, either.

As a rule of thumb, always aim for 100% sRGB.

LUTs

LUTs are like math multiplication tables. Sometimes you just don’t want to waste time or resources calculating something, and ‘looking it up’ in a table is faster. A LUT (Look-up Table) is just that. It maps one set of values to another. 2×5=10. If your video is 2, but your monitor is only capable of 10, you mathify (my term) 2 by 5.

There are different ways in which LUTs can be programmed and shown. Its basis is purely mathematical, but its use is totally subjective.

As a simple rule of thumb, if a 10-bit monitor has the option to display a 12-bit file via a LUT, it is not a bad thing. The monitor remaps the values as best it can. What many people forget is that this is still an approximation. Your monitor is still only 10-bit.

Think of LUTs as fancy toys, like lens filters. Useful, sometimes, but only if you know what you’re doing. Not mandatory.

Delta-E

In traditional science, whenever you see the term ‘Delta’, it means ‘difference’ or ‘deviation’. If today the temperature is 30 degrees and tomorrow it’s 31 degrees, the delta between the two is 31 – 30 = 1 degree.

Remember the EBU Grading classification we dealt with in Part Two? There were a lot of deltas in there. That’s because you can always specify a theoretical perfect value for each property – like color primaries, gamma, grey, white point, etc. In reality, however, monitors are allowed to deviate from the perfect value up to a point.

E.g. Delta-E for color primaries shows how each color deviates from the ‘perfect color space’ value. Every monitor, even the most expensive ones in the world cannot reproduce a space perfectly. You’ll never find anything in the universe with a Delta-E of 0.

The Delta-E of the human eye is about 1. The best color grading monitors should have a Delta-E of less than 3. The EBU requires Grade 1 monitors to have a Delta-E of less than 4. The Delta-E of the Dell Ultrasharp is about 4, which they represent as <5 for both sRGB and Adobe RGB. All the monitors on our list make the grade. The Dolby has an unprecedented (their term) delta of 0.2 or less.

Delta-E has many variations, the most used was ratified in 1994 by CIE so it’s called DeltaE94. Again, the value depends on how you measure it. Don’t take Delta-E as the law.

Gray scale Tracking

Different manufacturers measure these in their own way. The only thing you need to be concerned about is that the graph is as horizontal as possible, across whatever else it is plotted against. This shows uniformity. As you can see, no monitor on earth achieves a flat line.

Gamma

Display gamma is 2.2, which is the standard. To know more, read my primer on Display Gamma. All things being equal, a monitor that allows you to change gamma is desirable, for accurate calibration.

Bottom bottom line? Color graphs are to monitors as sensor megapixels are to camera manufacturers. Don’t believe everything you see.
Viewsonic

How to put all this information to good use

We’ve looked at everything a manufacturer will want to throw at us, and now it’s time to use all this information practically.

This is where we go back full circle, to Part One. Now you’ll appreciate why knowing your requirements makes everything else a lot easier. Let’s bring out the examples:

  • If you know you’re only going to work in HD for web videos, you know 8-bit 100% sRGB is more than enough.
  • If you’re working for HDTV broadcast, you know 10-bit 100% sRGB is great.
  • If you’re working for SD and HD broadcast in an NTSC region, you know you need 100% NTSC 10-bit.
  • If you’re doing the above in a PAL region, you can make do with 100% sRGB 10-bit, since PAL and Rec. 709 are pretty close. However, if your broadcaster is demanding, you might need a PAL-exclusive monitor.
  • If you’re planning on a theatrical release with DCI, you’ll need to conform to a DCI P3 10-bit color space.
  • If you’re a low-budget indie filmmaker with no option to grade in DCI P3, then it doesn’t matter where you grade. Seriously. No kidding. You have no control over the color delivery anyway, so why cry about it?
  • If you’re planning videos for mobile devices, use the intended mobile device(s) as reference, because they have their own gamuts. Generally, an 8-bit 100% sRGB monitor should be more than enough.

 
You’ll be amazed how a simple step like knowing your target audience can bring your choices to a very manageable level. You might only end up with three or four options all said and done.

Move on in the list. It’s pretty easy. Now, we’re in Part Two.

What size and viewing angle? Easy. Choose your location and viewing distance. Basic trigonometry, and you’ll know what ppi you’ll need, maximum. Find the monitors that deliver that and more.

If you are a high-end broadcast media supplier, you’ll find life easier if you conform to your broadcaster’s specifications. In this case, Grade 1 monitors. Obviously, you’ll also need access to Grade 2 and Grade 3 monitors for verification.

Finally, you come to budget. By now you should only have a few options left, which can be broken down according to what we’ve covered in Part Three and Part Four. You already know what to look for, so this step’s a bit time-consuming, but easy. If there are no monitors in your budget, then you’ll have to compromise. Compromise if you must, but don’t fool yourself.

How easy or hard has it been for you? What steps do you take before you select that perfect professional display monitor? Tell me about it.

 

One reply on “How to Choose a Professional Display Monitor (Part Five): Understanding Delta and Charts”

  1. The guide is extensive but absolutely worth it. The important thing it has taught me is to see through the marketing jargons for what I really need and not what the manufacturers think I do.

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