|
From: | Dave Arnold |
Subject: | Re: [ft-devel] gamma correction and FreeType |
Date: | Fri, 08 Nov 2013 10:12:12 -0800 |
User-agent: | Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0 |
I've attached a simple line pattern that I use to get a rough idea
of display gamma on various devices. For my laptop screen, at my normal viewing angle and distance, I measure 2.8 at the top, 1.6 at the bottom and 2.2 in the middle. LCDs have always varied with viewing angle, some technologies more than others. Luckily, the exact gamma is not too critical. I agree that your 1.4 image looks more balanced in weight than your 2.2 image. When I repeat this test with my tools, I find that 1.4 and 1.8 are pretty close, while 2.2 (like yours) tends to make the white text too heavy. (By the way, I don't know how to extract your images from the google docs page, so I'm just relying on what Firefox does on my display.) I've noticed this effect with white text before, and don't completely understand it. Some have argued that it is a visual perception issue. That could be. Another idea is that it results from a display transfer function that is not close enough to a pure power function. The physics of a CRT naturally generate a transfer function that is close to a power curve. But the physics of an LCD naturally generate a transfer function that looks like an 'S' curve, flat at both top and bottom. I understand that display manufacturers use electronics to modify this to get a better match to sRGB (which is very close to a power curve). But the closeness of the match varies and is never perfect. The greatest errors are close to the top end (white). I agree in theory that gamma correction should make the weight of black text and white text appear the same. But this is only one of many goals. Smoother curves and diagonals is another goal, as is cancellation of color in subpixel rendering. I believe that there is a single "gamma" function that will do all of these at the same time, because it is primarily a physics problem. Thanks. -Dave On 11/7/2013 10:29 AM, another gol
wrote:
|
GammaLines2.png
Description: PNG image
[Prev in Thread] | Current Thread | [Next in Thread] |