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428 · BIOMEDICAL SENSORS of the spectral response for that model of camera. While best-fit formulas like this have evolved and been perfected over the years by various manufacturers, it is illustrative of the empirical, rather than theoretical, nature of instrument calibration. 9.4.3. CURRENT CHALLENGES As indicated previously, details of the methods for conversion from signal to temperature remain in the realm of the manufacturers' proprietary information. As they strive to produce instruments of higher measurement accuracy (currently evolving to values better than ±2°C or ±2%), they are maintaining proprietary control of their signal data conversion algorithms, and hence their software. For example, one manufacturer has sold more than fifteen different software programs, most of which had data formats not directly compatible with each other, and some that could not even be converted with a utility. Some view this as positive marketing, maintaining control over the customer base and increas- ing profit margins on camera sales by selling high-priced software. Yet this philosophy is inhibiting the development and growth of generic specialty analysis software, especially for medical, electrical apparatus, machine, and building diagnostics. The need for a certain degree of proprietary control of signal conversion is recognized, and prob- ably essential. But if the industry is to mature, a universal standard 14-bit image format needs to be developed, allowing users to have generic software analysis capability in order to change values of emis- sivity, background, and optical transmission. Only then will powerful industry-wide software analysis tools emerge.