Hello!
Please help me with my problem.
I’m try to program my own software for FLIR  A40 using FLIR SDK and I want to find formula to calculating emissivity E2 with known jbject temperature T1,T2 and old value E1 (like a function “Emissivity calculation” in ThermaCAM Researcher).

In the user manual to NEC San-ei Image Processor software i'm find this: 

The intensity of infrared radiation coming from a point on an object is the sum of the radiation emitted by the object itself and the ambient radiation reflected by the

object:

I =E*I object  + (1 - E)I ambient

Where,  I object is the intensity of radiation coming from the object. I ambient is the intensity of radiation coming from the object’s environment. E is the emissivity of the surface of the object. I  is the intensity of detected radiation.

Note: The emissivity is in general a function of both the object temperature and

the frequency of the radiation, but in practice, it is regarded, to a good approxima-

tion, as independent of these factors for the materials and temperatures that are

likely to be encountered. We also assume that the contributions from atmospheric

absorption and emission are insignificant.

Equation above shows that in order to calculate the true temperature of a point on

the object from the detected intensity, you have to know the values of emissivity

and ambient temperature at that point.

If you know the value of the intensity of radiation coming from each point for two different uniform temperatures T1  and T2, you can calculate the values of emissivity and ambient temperature at each point on the surface of the object.

If to assume that the effect of the environment is uniform across the surface of the ob- ject, a single image at a single uniform temperature (but different from the ambient temperature) is sufficient to calculate the emissivity at each point on the surface of the object.

I’m try to integrate Plank’s radiation formula with wavelength range 7.5 -13 mkm (it's spectral range of FLIR A40 camera ) to find emmitance (W1) from the object with known temperature T1. Then I dived this emmitance to known emmisivity E1 to find blackbody radiations(Wbb1). Then I use integrated Plank’s formula for new temperature value T2 to find emmitance(W2) and i don't know what to do next

Please tell me is I choose a right way? and how I can finish this formula.

Sorry for my bad English. I’m just a Russian student.

Artem.