Hi Ryuji. I believe you might be referring to my recommendation of Lee Filters as a source of free samples of ND gels. They no longer advertise the sample swatch books on their website, but I'm sure if you contact them, they'll do their best to oblige.(posted 8068 days ago)If a scanner puts out truly RAW data, then the response should be linear. Any noticeable non-linearity will be down to offsets in the A/D conversion chain, together with light flare and possibly IR 'fogging', or breakthrough, in the higher density region.
If the 'raw' data are nowhere near linear, then the scanner software will have translated the native linear response of the CCD to a gamma function (most likely 2.2 or thereabouts), again with the inclusion of any offset. The only difficulty in measuring this gamma curve is in finding the zero density point, or white point, of the scanner. It's usually set somewhere around 0.1 ~ 0.15D absolute.
Once that's established, the transfer function of the scanner should be reasonably easy to graph.
Nearly every scanner autocalibrates its whitepoint with every scan, so repeatability should be checked over a period of time, and over a reasonable range of temperature.The problem of infrared punching through the dyestuff of any sample under test might not be trivial. The problem can be detected by sampling a known silver film image density, or a reference thin metal film density wedge, and comparing those readings with known densities of dye-image sample.