Linearization and characterization process of an image producing device
View Patent ↗Exemplary methods are directed to the linearization and characterization of an image producing device. In the method, a color test chart of the device is reproduced and measured based on a small number of color measurement fields with defined device color values. Associated color values are determined for each color measurement field and used to calculate linearization curves for the device. Additionally, by analysis of the device color values, the measured color values, and device behavior, an expanded color test chart with expanded device color values and associated expanded color values is calculated. The number of color measurement fields in the expanded color test chart is larger than the number of color measurement fields in the original color test chart. An ICC profile for the device is calculated from the expanded device color values and the expanded color values.
1. A process for linearization and characterization of an image producing device, wherein a colour test chart is reproduced which consists of a number of colour measurement fields with defined device colour values, the reproduced colour test chart is measured to determine colour values associated with each colour measurement field, wherein from the device colour values and the determined colour values a profile is calculated for the image producing device, wherein the reproduced colour test chart (TC) has a relatively low number of colour measurement fields and is reproduced and measured to obtain measured colour values, wherein based on the device colour values (Dev(i)) and the measured colour values (PCS(i)) of the reproduced colour test chart (TC), linearization curves (LC) are calculated for the image producing device, wherein based on the linearization curves (LC), an expanded colour test chart (TCex) with expanded device colour values (DevEx(j)) and associated expanded colour values PCSLex(j), is calculated based on the device colour values (Dev(i)) and the measured colour values (PCS(i)) of the reproduced colour test chart (TC), wherein from the device colour values (Dev(i)) and the measured colour values (PCS(i)) a gradient matrix (Dev2PCS) is calculated, the gradient matrix (Dev2PCS) describes the differential relationship between the device colour values and the measured colour values in a vicinity of a center of a colour space of the image producing device and is used to model the image producing device and calculate a conversion table, wherein the number of the colour measurement fields in the expanded colour test chart (TCex) is significantly larger than the number of the colour measurement fields in the reproduced colour test chart (TC) and wherein the profile for the image producing device is calculated from the expanded device colour values (DevEx(j)) and the expanded colour values (PCSLex(j)).
2. The process according to claim 1 , wherein based on the device colour values (Dev(i)) and the measured colour values (PCS(i)) of the reproduced colour test chart (TC), a linearized test chart with linearized device colour values (DevL(i)) is calculated, and by modeling of the image producing device, corresponding linearized colour values PCSL(i) are calculated, wherein from the linearized device colour values (DevL(i)), the linearized colour values (PCSL(i)), and the gradient matrix, the conversion table (Device 2PCS) is calculated which represents a relationship between the linearized device colour values (DevL(i)) and the linearized colour values (PCSL(i)), and wherein the expanded colour test chart (TCex) is calculated by way of the conversion table (Device2PCS) with the expanded device colour values (DevEx(j)) and the associated expanded colour values (PCSLex(j)).
3. The process according to claim 1 , wherein the linearization curves (LC) are integrated into output curves of the profile (P).