Improving Scanner Color Reproduction

In the previous post, the scanner profile was created with the same 343 patches that were used in MP4.8 for creation of rgb printer profile.

The MP reference patches are evenly distributed in the RGB space. In contrast, PM5 has more reference patches placed along the neutral and the 3 primarily axes, as shown below.

The patches were combined to form a larger reference target for generating  the scanner profile and the effect was analysed.

Results
.  The reference RGB values were extracted from the target112 tiff file.
.  The printed copy with the target112 was measured with a spectrometer, dtp41.
.  The printed copy was scanned and RGB values were extracted.

Conclusion
The extracted RGB values from the scanned data with dedicated scanner profile exhibit good correlation with the spectrometer's measurement data.

Better Color Matching with Delicated Scanner Profile

Metamerism is an optical phenomenon which occurs when color of two samples appear to match under one light source (illuminant) and not match under another.

All photographic media are prone to metamerism to some degree.The created scanner profile may work unsatisfactorily if the image to be scanned is of a different material from the reflective IT8 target.

With the appropriate choice of targeting media for scanner profile creation, a high performance scanner icc profile can be generated, as illustrated below.

Test Pattern
Here is the custom test pattern that was used for the evaluation. It consists of total of 112 color patches.

Both plots were generated with the same scale

Profiles Under Evaluation
In the following test, the Test Pattern was printed with CP800 dye-sub printer and with PhotoShop CS4 using custom printer icc profile. It was scanned with an Epson V500 and the acquired image was assigned with the respective scanner profiles before converting to the working color space for RGB values extraction. The extracted RGB values were then compared with the measured data. Comparison was carried out with PatchTool and ΔE2000 standard was used  for checking differences in color matching, whereas actual color measurement was performed with a DTP41.

1) V500 generic profile
2) PM5-IT8, profile was created with Kodak IT8 reflective target.
3) MP-IT8, profile was created with Kodak IT8 reflective target.
4) Arygll-IT8, profile was created with Kodak IT8 reflective target.
5) Arygll-CP800-343, same paper medium was used for both scanner profile creation and test pattern  printout.

Comparing measured data and extracted RGB values

Above results show that reproduction of color for scanner can be improved significantly if the scanner icc profile is created with the same printing media that are used for generating the scanned images.