ISO 18946:2012 describes test methods for evaluating reflection colour photographic prints with regard to changes in image appearance resulting from exposure to both low and high relative humidity.
The observed changes relate to colour, tone and loss of sharpness caused by horizontal and vertical diffusion of colorants from exposure to elevated humidity levels. Other humidity-related factors are outside the scope of this test method.
The method and procedures described in ISO 18946:2012 are particularly appropriate to systems where the colorants are applied by a mechanism involving the diffusion of colorant into image-receiving layers and to certain types of inkjet media that are susceptible to Dmin yellowing.