Talk:Contrast ratio

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is this the ANSI contrast? Actually, the darkest color is black, and that means zero luminosity (should be not hard to achive)... the contrast then would have an infinite contrast ratio. thus i guess the contrast ratio isn't that good in telling you about the quality of a display - or am i wrong? thanks, --Abdull 13:34, 26 Apr 2005 (UTC)

It's quite difficult to achieve zero luminosity using any display technology. For example, in DLP projectors some light will reflect from between the mirrors, and some will reflect from the very mirrors themselves. Reflection from aluminum is not completely mirror-like (specular reflection), there will be some diffuse reflection as well, meaning that mirrors that are turned away in a [[DMD] device and that should look totally black, will scatter a little light into the screen - maybe 0,05% of the amount if the mirrors would be turned the other way (figures not checked). Santtus 22:05, 24 July 2005 (UTC)

Actually CRTs achieve a theoretically infinite contrast ratio and practically achieve enough of one to make such quantification pointless. (comment 23:53, 8 January 2006 Zbobet2012)

Checked that fact, you're right. I found something lot more interesting tho. I'll re-arrange the article later on.. lots of stuff that needs to be added. I'll work on that. Added some references already.

The static contrast ratio of the eye is just about 0,5-2%, so that a display with 200:1 contrast ratio would suffice, if the average light level in the image would stay the same. The overall light level in the image usually changes, so greater ratios are required. The eye adjusts to various light levels to the extent that about 10^7:1 ratios can be achieved, but mass produced display devices are incapable of such contrast ratios. This is explained to better depth in here [1].

A presence of single candle in an average room will render 30000:1 (or infinite, for that matter) and 500:1 displays indistinguishable from each other. In a typical brightly lit office only contrast ratios of 10:1.. 30:1 can be achieved. In this situation, the determining factors are the ambient light level, reflectivity of the display surface and the maximum luminocity the device is capable of. The slight variations in the lowest blackest levels would be totally lost in the presence of ambient light 10 or 100 times more than that of the device. Santtus 11:58, 11 January 2006 (UTC)

Contents 1 Removed the unsourced template 2 New reference format 3 This sentence 4 Good article 5 Extraordinary contrast ratio 6 Local contrast 7 Methods of measurement

[edit] Removed the unsourced template

I added sources to perhaps one half of all the statements that could use one. I'll try adding some more references soon. Santtus 12:06, 11 January 2006 (UTC) Oops, sorry I'm late from addding references. Btw one thing.. I guess that someone mixed having ability to resolve brightness levels 1% apart (1:100) and having 100:1 resolution. Santtus 21:15, 5 March 2006 (UTC)

[edit] New reference format

I've updated the first couple notes to the new format, which can match up the numbers more accurately. Shawnc 23:19, 20 April 2006 (UTC)

[edit] This sentence

"This may not sound too bad though, as the static contrast ratio of a human eye is somewhere between 100:1 - 1000:1 so the details in those highlights might not be resolvable anyway." This can probably use a citation and be re-worded a bit, in particular "sound too bad" and "might not be resolvable". Shawnc 00:06, 21 April 2006 (UTC)

That 100:1 - 1000:1 thing was from an article, although I summed up the controversy surrounding the issue. I'll try to look at it soon enough. Santtus 15:12, 26 April 2006 (UTC)

You may want to edit the article on eye as well, because it states only the 100:1 figure. GreenGrass 14:58, 7 May 2006 (UTC)

Was in the middle of editing, but I couldn't finish my writing before getting a headache ;) I'll finish it later. I checked from various sources that 100:1 seems to be fine - it's the most often quoted value. Found some info on contrast sensitivity too, but it measures minimum noticeable contrast, not maximum. Now I just got one more question. How do you define maximum contrast a person can see? I'll try to find an answer for that.. Santtus 13:18, 9 May 2006 (UTC)

Well, as the performance of an eye is apparently limited by the performance of its lens, it should be easy to measure its static contrast ratio. You can fill 50% of your FoV with a white object, and 50% with a black object (with sufficiently high ratio between their diffuse reflectivity). Then you place a small text on the black object with a brightness just a bit more than the background. Afterwards, you gradually increase the brightness of the text until it becomes resolvable (in layman's words: "readable"). Than you measure the contrast ratio between the luminosity of the text and the luminosity of the white object, multiply it by two, and there you have it. (I took the last number from my head, it should be the minimum contrast necessary for the eye to detect edges of letters, which is probably a bit subjective issue). GreenGrass 19:55, 15 May 2006 (UTC)

[edit] Good article

Good job on the article. I would start working on correcting grammar & etting some pictures.

[edit] Extraordinary contrast ratio

It appears that the phrase "extraordinary contrast ratio" doesn't mean anything special, except that a someone feels that the contrast ratio is great. I've found no examples of professional use of that phrase, so I'll revert the changes unless I'm otherwise convinced. Santtus 09:12, 13 June 2006 (UTC)

[edit] Local contrast

The article should mention the difference between local and "global" contrast (both spatial). Local contrast means contrast near differences between luminances. For example, if there is a white box on a black background, local contrast is the contrast close to the border between the white and the black areas. Global contrast is a bit like dynamic contrast, except both bright and dark areas may exist simultaenously - contrast is measured where the differing luminances don't "contaminate" each other. CRT monitors may have infinite global contrast because of the ability to turn off the electron beam completely, but they have worse local contrast than LCD displays, because due to internal reflections bright areas have halos which contaminate the dark areas. ANSI contrast measures local contrast unless the checkerboard pattern is very sparse. Global contrast should still be differentiated from dynamic contrast, because for example even if you adjust the backlight of an LCD monitor to achieve a high dynamic contrast, it won't help you if you have bright and dark areas at the same time. The great thing (for CRTs!) is that out eyes have low local contrast and high global contrast. This is also exploited for LCD monitors that are backlit by LEDs. Since there are fewer LEDs than pixels, the local contrast is low, but the global contrast can be great. A local HiFi magazine measured each three contrasts for the televisions they reviewed. This online article also highlights the differences between local and global contrast (in the article they're called contrast and dynamic range respectively): http://www.displaymate.com/ShootOut_Part_1.htm As you can see, the CRT has a global contrast of ~18,000:1 compared to the LCD's ~600:1! But a 9x9 checkerboard pattern demolishes CRT's local contrast, reducing it to ~100:1, while the LCD retains ~600:1 —The preceding unsigned comment was added by 84.231.81.152 (talk • contribs) 23:46, 3 December 2006 (UTC).

[edit] Methods of measurement

This paragraph:

Many manufacturers of display devices favor the use of the full on/full off method of measurement, as it will effectively cancel the effect of the room completely, giving as high ratios as possible. Equal proportion of light will reflect from the display to the room and back in both measurements, as long as the room stays the same. This will inflate the light levels of both the "black" and the "white" measurements in the same proportion, unaffecting the black/white luminance ratio.

is simply not true! If Lw, Lb and Lr are the white, black and room luminosity, respectively, then Lw/Lb might be very different from (Lw+Lr)/(Lb+Lr). The reason manufacturer prefer this contrast measurement is that it might give them higher contrast, than say the ANSI contrast. See for example the CRT (global) contrast vs. LCD (global) contrast in the previous comment.

I would suggest the following phrasing:

Many manufacturers of display devices favor the use of the full on/full off method of measurement, as it will give higher contrast ration over the ANSI contrast measurement method.