Fridtjof Busse wrote:
For example: If I use the profile produced by Argyll, many of the numbers on the testchart  are invisible, while the profile from basICColor shows even the "1" (though very weak).
There are many possible explanations for this, but without further information it's hard to guess what your particular situation is. One issue is that the test chart you refer to is an unknown. It's unknown what situation it is intended for. What gamma is it encoded in ? What display brightness is it intended for ? What viewing environment is it intended for ? If any of these things don't match your situation, the chart may be difficult to read. It's also not clear whether you are talking about calibration or profiled behaviour. The latter can be affected a great deal by the way that profiles are linked (ie., whether the source to destination black points are being mapped to each other.) If you're talking about calibration only, then there are still several variables that could explain the difference, such as a difference in target parameters, even though you say you've tried to match them. Note for instance that Argyll defaults to a Gamma target of 2.4 on non-Apple machines, a number suitable for viewing typically encoded images in a darkened viewing environment. This is slightly higher than the defaults of some other software, and results in a slightly higher contrast that may make a chart intended for display at a lower gamma hard to read in the shadows. Also note the lack of agreement on how real world gamma's are measured. The default 2.4 target in Argyll is an effective gamma value, not a technical gamma value (ie. the curve shape won't follow a power of 2.4 once the non-zero black is accounted for, but the mid level brightness of the actual curve used will match that of the theoretical ideal power curve.).
Any way to determine why the profiles are so different? Thanks.
If it is the profile (rather than calibration), then the basic measure of profile quality is how accurately it represents the display behaviour. The usual way to evaluate this is to measure the display (ie. generate a test chart and then used dispread), and then verify against the profile <http://www.argyllcms.com/doc/profcheck.html>). Graeme Gill.