Whre are the specs for absolute blacks??

Voo

Standard Member
I've seen lots of impressive sounding contrast ratios for LCD projectors lately (5000:1, 7000:1, 10000:1 etc......) but these claims seem somwhat suspect, or, at the very least, misleading e.g. you would expect the absolute black levels of a 7000:1 contrast projector (say...the Sanyo Z4) to out perform one rated at 4000:1 (say...the Optoma H79). As far as I can tell, this is simply not the case, in fact, from experience so far, the Z4 barely matches the absolute blacks of the Optoma H30 let alone the H79 (incidently, i've seen the H30 vs Z4). Isn't there some sort of standard by which these absolute blacks can be compared or is it simply impractical :confused: Sorry if this issue has been brought up before but i'm finding it hard to compare LCD and DLP contrast specs. Black levels are an important issue when selecting a new PJ and as far as I can tell, DLP still have the edge by quite a considerable margin, inspite of what the specs might tell you (have DLP missed a trick here in the way they advertise their contrast specs??)..........Any thoughts :lease:
 

JiveTalker

Standard Member
Voo said:
I've seen lots of impressive sounding contrast ratios for LCD projectors lately (5000:1, 7000:1, 10000:1 etc......) but these claims seem somwhat suspect, or, at the very least, misleading e.g. you would expect the absolute black levels of a 7000:1 contrast projector (say...the Sanyo Z4) to out perform one rated at 4000:1 (say...the Optoma H79). As far as I can tell, this is simply not the case, in fact, from experience so far, the Z4 barely matches the absolute blacks of the Optoma H30 let alone the H79 (incidently, i've seen the H30 vs Z4). Isn't there some sort of standard by which these absolute blacks can be compared or is it simply impractical :confused: Sorry if this issue has been brought up before but i'm finding it hard to compare LCD and DLP contrast specs. Black levels are an important issue when selecting a new PJ and as far as I can tell, DLP still have the edge by quite a considerable margin, inspite of what the specs might tell you (have DLP missed a trick here in the way they advertise their contrast specs??)..........Any thoughts :lease:
If you search through earlier threads you will find LOTS of details about contrast ratios. The values in specs from manufacturers do not correspond to any real world performance. For example, the more recent LCD projectors use a digital iris to extend there CR ratings but an iris can't be both open and closed at the same time so you can't get the very brightest levels and very darkest levels at the same time so it has to make a best guess choice. However, the iris in your eye isn't good at dealing with very bright and very dark at the same time either so it shouldn't often be a problem. The only meaningful figure to compare is "ANSI Contrast" which is measured in a more objective manner. I'm sure others could explain this in a more technical fashion but I think I've got the basics right.

Last night I went to a bar with my girlfriend and they had three NEC (DLP?) projectors in use. I'd told her about issues with black in ambient light and she said she couldn't see what the fuss was about as she couldn't see a lack of black in the picture at all due to the brightness of the other colours. Hopefully she'll like the Z4 that I'm getting tomorrow then... :D
 

LV426

Administrator
Staff member
Contrast ratio isn't directly related to "black" anyway.

If you had (say - just for illustration)

Projector (A) which does black with a brightness level (any measurement) of 1 unit
Projector (B) also does black at brightness of 1 unit of measure

Projector (A) does absolute WHITE at a brightness of 2000
Projector (B) does absolute WHITE at a brightness of 4000

then clearly, the black level is the same in each case, yet the contrast ratio is wildly different.

Perfection in black level is nothing more or less than the total absence of projected light.
 

Peter Parker

Distinguished Member
Although contrast ratio tells you the difference in levels from white to black, you need to know how bright it is at white to be able to determine the actual black level.

As Nigel above has shown, if you have a projector with 1000 genuine lumens (not advertised which are measured when the pj is not set for video), and a CR of 2000:1, the black level will be 0.5 lumens. If another projector with 1000 genuine lumens but a CR of 4000:1, the black level will be 0.25 lumens provided the white level is the same (they're both at the same brightness).

So to compare them you need to have them at the same level of brightness. One way to do this is to add a lens filter so that it will dim the projector down thus reducing the black level at the expense of overall brightness.

Just to add - the advertised figures are measured before the pj is set for video. In order to get all projectors at the same bench mark they need to be calibrated to D65 which is the colour temperature of white in a specific point in colorspace. Contrast ratio measurements can then be directly compared between machines, as can the lumen output, provided that too is calibrated for white and black levels (contrast and brightness settings). That still isn't a direct comparison for absolute black since the lumen output of the machines will vary, but the measurements will tell you what levels can be achieved along with reflectance levels from the screen.


Gary
 

Voo

Standard Member
Thanks for the info guys, I probably should have done a search on the subject first. Your patience is much appreciated :) I still think DLP has the edge however on absolute blacks (or the absence of light)......if it weren't for all the rainbows i'd seriously consider one. Thanks again, Voo
 

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