in-depth it can actually be. But when it comes down to it, this isnt nuclear engineering, everything does not have to be perfect according to the measurements gave by expensive equipment. What is necessary is the user likes the image.
The problem is some of our DIY PJs settings are so out of whack, we dont know a good place to start to get it to the point where we like it (even if it isnt "perfectly" calibrated).
one very important aspect is our display gamma. If this is off our picture will not look correct. Display gamma for TVs and PCs is between 1.8 and 2.2. Macs are 1.8, CRT TVs are usually 1.8, PCs with a CRT are usually 1.8-2.0. PCs with an LCD are usually between 2.2-2.4. Film (DVD) and HD content should have a display gamma of 2.2! So we should aim for 2.2 or close to it.
We have all heard the complaints:
"my image is to dark, no shadow detail". It is highly likely your gamma is 2.5 or higher (2.8 even)
"my image is washed out, even dark scenes look grey". It is likely that your gamma is to low 1.5 or
lower.
Now brightness (black level offset) and contrast (luminance multiplyer) settings can affect these as
well, but even if brightness and contrast are optimized; if our display gamma is not close to 2.2 our
image will look ... well... like crap.
What is gamma? Gamma is the non-linear display of the brigtness of our screens from IRE levels 1 to 100
(or RGB levels 0 to 255).
Why gamma of 2.2? There is a long history behind it (all the way back to the 50's and the origin of
NTSC TV standards), but the bottom line is, we do not see brightness linearly, so to get the most vivid
image to our eyes (in a dark room) a gamma of 2.2 is used.
Here is a picture of some gamma curves
As.... i forgot what i was saying....
Next thing, what greyscale range are we in.
for computers its 0-255
for video DVD's (sometimes) its 16-255
this is kind of a grey area, because if you play a DVD through a computer, what is actually black, 0
or 16? I will need some help here. Either way, you need to adjust brightness and contrast to make sure
you see the full range.
Next is color balance, which also affects color temperature 6500K is our aim. My ushio s400DD has a green push, and an undersaturated blue. So for a correct
color balance I had to lower the green setting on my controller board (optimally a color filter would be
used instead). This reduces the amount of colors displayed, and reduces overall contrast ratio (color
contrast ratio). But the sky is blue now, and not sea green (you get the idea). Using a digital camera
with cloudy (6500k) or daylight5200k) white balance, and a picture editor, we can look at the histogram and see the
intensity of each color. We can also use a lux meter and measure the gamma curve of each color. The
human eye "adapts" to color and brightness. So even if the PJs colors are off, they will look OK after
a few minutes. A quick test is to look at your nice PC LCD screen (white screen) when go look at your PJ
white screen right away. Your PJ screen will probably look murky at first (green tint in my case).
Then a few minutes later it will look perfectly white. Once we adjust the color balance it should look
perfectly white right away after looking at your PC LCD screen.
As of now I have made a small excel program to see the greyscale and color gamma curves using a CIE
luxmeter.
I still am going through the procedure to calibrate our PJs. I also want to put together some comarision
pictures of normal, high and low gamma curves. Along with brightness and contrast (white and black
crush). So we can all get visuals of how these settings affect a picture.
More to come soon
