Originally Posted by K1NeT1C USMC
And how about gamma? The last disc you guys had had a gamma test but it didn't work too well. It would change when ever I changed the sharpness
Just to add to what Stacey said, these quick gamma checks where you compare a high-contrast pattern to a solid gray are really just a way of getting a rough idea of the actual gamma. We debated having them at all, but we decided we find them handy so we should include them.
You just need to know what their limitations are. They don't work well at all on LCOS displays. As you point out, sharpness can throw them off. Scaling can throw them off. However, scaling and sharpness usually throw them off by a small amount, so you can still get a rough idea. If the pattern says gamma is 2.4, you know it's in the 2.3-2.5 range. LCOS, however, just doesn't work right with these patterns. It appears that an LCOS cannot keep local contrast high enough in fine-grained patterns. For the vast majority of content, this is a very minor issue. Most real content doesn't have high-contrast fine patterns, and even if it does the small contrast loss doesn't ruin the image. But for these gamma-check patterns, it just throws the whole thing off.
You can actually measure gamma much more accurately using a cheap light meter than you can with one of these check patterns. I keep thinking I'm going to write a guide to using a photographic light meter to measure gamma, since most people are never going to buy an LS-100, and I suspect you can get a good enough result using a simple old-fashioned meter you can get on ebay for $20. Some of the old meters no longer have high absolute accuracy because of aging of the light sensors. But their relative accuracy is fine, and that's all you need for gamma measurement. The problem is that they're often not labeled in units that are easy to use. EV, for example, is a logarithmic scale that has a non-obvious relationship to something absolute like foot-lamberts. But I can make a spreadsheet that will do the conversions.