Image Quality, Contrast Transfer, and Tone Reproduction

Tone Reproduction Curve (TRC) of an imaging system is an accepted way to describe its quality capabilities. Such applications were first developed in Photo Science for tonal images and then applied in Graphic Arts for halftones. The TRC is, in a sense, a description of a system in an amplitude domain of densities. Conventional attributes of halftone imaging systems (i.e. dot gain, print contrast) use the TRC for their definitions. Recently, descriptions in a spatial frequency domain became useful tools in image quality assessment. One of them, the Contrast Transfer Function (CTF) led to a single number quality merit factor (QF) for halftone imaging systems. The QF number describes overall image capabilities and can be measured for ink - paper - press, plates, proofing, etc. The integral character of the QF number apparently is masking conventional attributes of imaging systems. Current study connects the CTF with a TRC of a halftone imaging system. It shows how a TRC for an arbitrary screen frequency can be evaluated from the measured CTF. The applied value of the study is in a procedure for adjusting a scanner to fit a given in - paper - press performance.