This is also posted in the Neutral Gray thread as well. A lot of topics overlap each other and are very much intertwined. Some people may not be interested in a particular thread, so they may never see certain information. Normally I would just post a link, but this is key to screen color balance in my opinion and this is definitely on topic in here.
A quick note: There has been some recent talk by some that RGB is meaningless and shouldn't be used. I disagree. It is an excellent way of presenting a 'snapshot' of a color. Not only does it give us a visual representation of what a color looks like, it also gives us a quick indication of that color's balance. RGB alone doesn't tell the whole story, and for those of use doing testing and research we tend to dig deeper and go into some areas that quite honestly most people just don't care about. So in that sense RGB is perfectly fine in my opinion as a presentation tool and quick color balance indicator, but it certainly is not what everything is solely based on.
There was also some debate on conversions. Some of the charts and numerical values may change slightly and I will update them if that is required. Still the "V" theory is a sound principle. I have discussed this with a few college professors that teach light and color theory and they agree with the concept.
So what is the 'V' curve, and why do I feel it is important? First let's take a look at the typical Home Theater. A Home Theater that is comprised of a front projector has many components and variables that ultimately determine the overall performance. Some items and elements we can control, like the projector's color balance, brightness, contrast, gamma settings and so on... and then there are other items that are harder to control or in some cases impossible, such as sunlight, room layout, etc. We really shouldn't be using the screen as an 'adjustment', only if there is a reason to do that. The color balance of a screen may be one of the most critical items in an entire home theater setup. If the screen skews the colors of the projected image, it is not a very good screen. Ideally we want a screen that reflects the projected image the most accurately and efficiently- accuracy for the image color, and efficiency for the overall brightness.
White screens are the easiest and most forgiving, but even they need to have a good color balance or it can shift the projected image's color.
There always seems to be an ongoing debate about color balance, especially with gray. Either about its ambient properties, or that it takes more than gray to make an ambient light screen, or it kills whites and makes images look muddy… to it is the best type of screen a person could have. So who’s right and who’s wrong? Everybody and nobody.
A lot depends on a person’s personal tastes and what they like. Gray undeniably helps with black levels and perceived contrast for projectors with less than stellar contrast ratios. It is also better with lighting in a room and can deal with ambient light better than a white screen can. I still do not feel this makes it a true ambient light screen, but as stated by others I agree it is better than a white screen and more appropriately should be called
'ambient light friendly'. What is important and something every DIY method should strive for is color balance.
I find it interesting that neutral gray is viewed by some as the Holy Grail of gray screens. This has been debated for a long time now. Some have gone back and forth in this debate, stating neutral is the way to go and then later questioning why the importance of a neutral. I have questioned this myself since manufactured screens are not completely neutral. If you look at the color curve once the spectrophotometer values are converted to RGB, most have a distinctive ‘V’ curve. So the question is why would they do this? Here are some explanations I got:
- They did it on purpose- so the screen will look good even if the projector is off a little. A red or blue push doesn’t look too bad, but a green push kills skin tone- and this is how many people judge image quality.
- They did it accidentally- when gray came into popularity, they just used the most common standard, which is illuminant C (6774K). Many commercial grays are almost exactly on for illuminant C, but there are some that are not…
- Probably the biggest reason, most projectors have a green push out of the box. Since many people just run through a quick calibration, and most of the time just by eye, it makes a screen the easiest to calibrate to for the widest range of projector's and users.
Here is what those pushes can look like as compared to the correct image.
Correct Color
Red Push
Green Push
Blue Push
Red is the most acceptable and forgiving to a point. Some people actually prefer a cooler image, so they may not mind a blue push, but green is definitely a bad thing to have any type of push in. Seeing that some Director's and Director's of Photography film with a blue tint (check out the Terminator movies sometime, especially T2, it has a distinct blue tone to it) a screen that already pushes blue would certainly take the movie image over the top and beyond what the Director intended it to look like. In some cases to a point that is unwatchable to some people.
Hopefully the reason why screen color balance is so crucial is starting to make sense.
So I asked the question if commercial screen companies aren’t concerned about their gray’s being totally neutral, should we? That’s like the opening statement about who’s right and who’s wrong… yes we should be concerned, yet no we shouldn’t… but both of those answers have a reason in my opinion.
If we look at what I call the ‘V’ curve, we see there is a green deficiency, but usually the red and blue components are relatively balanced. There are instances where a slight blue push, or a slight red one, (or a slight deficiency) can be beneficial, but mainly it would be more of a user preference. A slight red deficiency could help some with incandescent lighting since it leans in that direction, while a slight blue push can make whites appear ‘whiter’ (another color conditioning we all have had since we were born). The trick and key is knowing when the push is too much.
A few years ago DIY was dealing with these questions and ideas, but for the most part there was no data. The spectrophotometer tests that have been done recently, as well as the converting of that data to RGB values has done a lot in the way of understanding screen balance as well as now knowing the color composition of DIY methods. RGB is widely debated by some as being useless when discussing screens. I disagree. It’s hard for the average person to understand CIE data and looking at those numbers isn’t easy for someone not used to what they mean to determine if a color is pushing to hard one way or another. RGB makes it easy to quickly see the color curve. If the ‘V’ is in line with typical commercial screens, then yes that color would most likely make a nice screen- as long as the color itself isn’t some wild off the wall color. If it is a white or gray then I would have no problem using it as a screen.
So I just completely contradicted myself when it comes to neutral colors vs a well balanced color? Not really. Even though it was just stated that many screens tend to have a slight green deficiency, that doesn’t mean a neutral color is bad… just that the commercial companies strive for the best image across the widest range of projectors AND consumers tastes. As stated earlier, green can push hard even with the slightest increase in RGB value. Most people only do basic calibrations. This way the commercial screen looks good out of the box to most users and projectors.
Seeing color is a sensation, like hearing, taste, or smell. Sensations are not felt the same way by every person. Food tastes differently to each person. In the same way, there is no absolute color that is inherently seen the same way by every person. Nor is every person’s vision the same. This is where neutrals come into play.
Neutral gray will eliminate/reduce color contamination from reflected light. Even though slight variances in screen composition and colors will work fine, a neutral palate is the best at reflecting the colors back the most accurately.
Also different light sources affect the colors that you see. For instance, a color viewed under fluorescent light will look radically different when viewed under incandescent light. Fluorescent light adds green to colors while incandescent light adds red. (This is why a slight red deficiency in screen color can be helpful with incandescent lighting)
A front projection Home Theater system consists of several devices that all deal with color at some level, and in different ways. Projectors deal with colors being created by light, and the screen deals with colors being reflected by pigments. Because all of these components in the system handle color in different ways, color reproduction between them is not so obvious. They use different color models, have different color gamuts and different Gammas. Moreover their colors are influenced by calibration settings and environment. Again neutral colored screens reflect the light from the projector with the least amount of color skewing. The other option is a screen that has a good color balance.
I am not abandoning any previous research and testing I have done. I think both can coexist… as long as the ‘V’ curve isn’t radically pushed by the red or blue components it will work just fine. Neutral grays however will allow us to go darker with fewer color problems than if the gray is not neutral and meant to be an aesthetically pleasing color as a wall paint. Also a neutral color reflects light the most efficiently, therefore the image tends to be brighter even with darker shades of gray.
Many people have been searching for neutral grays for a long time now. It’s not that they didn’t know what they were looking for; it has more to do with technology and more readily available data. Now we can actually see spectro data and the color breakdown where a couple of years ago that type of data didn’t exist in the DIY realm, at least not from what I have seen. So both a neutral screen or a well balanced screen or 'V' curve screen will definitely work, and like I said earlier, everyone’s tastes are different. I know when I finally found a ‘compromise’ with one gray paint I used, it still wasn’t optimal. Even though I probably could have gotten used to the color shift, anyone else walking in for the first time would most likely see it was off since they were not ‘adjusted’ to the screen themselves. To me that is a bad screen. People should not be told ‘Well you’ll get used to it…’ there should be no reason to... and that is where color balance comes into play and is so important.