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Old Oct 26, 2003, 2:39 AM   #1
Frank Doorhof's Avatar
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Default Buying a digital display.........


At the canon forum we had a discussion about what to use a CRT or TFT display. I have always been a very active CRT fan and user and would never think about getting a TFT now. However after some major problems with my 22" monitor (twice defect from new) I tested some TFT's and finaly bought a Iiyama 20.4" TFT with the 600:1 contrast ratio. Although blacklevel is worse than my CRT overall I'm very happy with it.

The discussion went on about the incorrect colors on TFT's in general, this however should not be true, that's why I explained a little bit about how colors are made on a display. I think it could also be nice to post it here for the general public.

The contrast ratio is the difference between full white and full black.
If you want this correct you should measure a checkerboard of white and black squares and measure those.

Than for example:
Black 0.5 ftlmb and white 30ftlm will yield a contrast ratio of 60:1. This is the right way to do it.
Most manufacturors however measure a full on full off method, meaning they raise the contrast VERY high, even beyond the punt of clipping and measure a full white screen, after that they will measure a full black field, thus getting very high contrast ratio's.

In real life the contrast ratio is VERY important especially for photo work, with a 150:1 contrast ratio blacklevels will be very poor and color fidelity will be dull, on a 1300:1 contrast ratio black level will be totally black, and the color fidelity will jump of your screen.

600:1 for a TFT is very very nice to look at, with very good blacklevel (except in a darkned room) and lively colors.

Most problems however with digital display's is the primaries reading.

There is a standard for Red Green and Blue called the SMPTE standard, this is measured in a CIE chart.
This chart will give you a Green, Blue en Red point in the total gamma of colors.

Ok to understand the working of monitors read on.....

We see only 3 colors, Red, Green and Blue.
We are VERY sensitive for Green, less for Red and only 11% for Blue.
This is also shown in the CIE chart, Green on top, Red higher than Blue and Blue on the bottom.

With the right combination of these 3 colors we can make white, all the combinations of white can be seen along the black body curve, the black curve in the middle. To understand calibration and color it's important to understand that green is no part in the measurement on an analyzer. That's why we don't talk about 6500 degrees on a monitor but on D6500, meaning this is an EXACT co÷rdinate on this black body curve.

With this point as a reference we can get almost every display dialed into this point. Meaning that when measuring a grayscale it will read D6500 over the total scale from black to white (+/- 400 degrees can be called rather good tracking).

Still this is not the complete truth, although most people stop here.

One VERY important thing (maybe the most important thing) is how the primaries are displayed.

When taking a fosfor based CRT projector for example we have 3 tubes, one Red, One Blue, One Green. All these tubes are often filtered to get the exact green, Blue and Red co÷rdinates of the SMPTE standard. When combining this with the D6500 calibration you will have PERFECT color representation.

The problem is in these primaries for digital display's. Often for example green is much to high, meaning that green will be too much on a display, this will give everything on the display a greenish tint, this is often seen in the older TFT monitors.

It goes even further away when green is not above the SMPTE point but goes to the right under that point, everything that supposed to be green will be yellowish (a problem of almost every digital projector).

It can even get more bad when also red is not in its position making the triangle totally out of balance, Colors will look very unnatural with yellow and orange casts, what should be green and red.

If you search out for a good TFT you should always try to find out how it's primaries are displayed, this is however information the manufacturers are not giving. When not having an analyzer you should therefor make a picture with a grayscale in for example 10 steps, and a few areas with intense green to less green and the same for red and blue (also for example in 10 steps).

You can than easily see color casts, it's not an exact science (an analyzer is) but it will show you that 50% of the TFT's will be out of the question immediatly.

Also it would be nice to have a bar with a gradiant fill without steps, to check the possibility for the TFT to show colors without banding, or digital steps.

Hope this helps a bit.
Sorry for the long story.

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Old Oct 26, 2003, 3:39 AM   #2
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There's been a lot of discussion about this in the General Q&A forum with CRT winning. Suggest you search for CRT LCD in that forum to see what has been written there.
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Old Oct 26, 2003, 3:49 AM   #3
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I really don't care what wins or what not (not meant negative) I know that on most points the CRT will rule over the TFT's for a long time (if not for ever), but there are other things to take into consideration.

It's impossible for a CRT to have coloruniformity over the total area, while TFT's have that, the focus on a TFT is much better than any CRT.

On the other hand, CRT's will yield standard much better colortrueness, will have much more detail in the same resolution as a TFT because it's not a fixed pixel display. Will have better black levels alway's, will have a MUCH higher contrast ratio.

The standpoint of TFT is NO good for photo use however is overdue. One advantage of TFT's for example is the portrait option. Did you ever see a 20.4" TFT (1600x1200 600:1) in portrait mode , I can promise you it will blow you away.

I miss my CRT everyday because I know it could be better for half te money, on the other hand, I absolutly love the crisp and colorcorrectness of THIS TFT, I miss the blacklevel of the CRT.
It's a win-loose situation in both directions. Whilst a year ago it was a loose-loose situation for the TFT.

I was 95% happy with my 22" pro Iiyama I'm 90% happy with THIS TFT, I used a 17" TFT before this one (Because my Iiyama broke down the second time in 8 weeks) and hated every minute working on it, I even stopped working on my photo's for a week. With this TFT the story is different, I calibrated it and tweaked some settings in the card setup and at the moment I'm blown away with the results, as with the CRT the printout and what I see on screen are DEAD on, except in the deepest black, but therefore I use a second CRT monitor if needed (I always have 2 monitor's hooked on).

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