Tonal Gradation Curve

It describes the way tones in the original are matched to tones in the reproduction.

• Setting the tonal gradation involves controlling the placement of end points (i.e. lightest and darkest) and adjustment of the intermediate tones to meet the needs of the reproduction.

• The tonal range that can be reproduced depends on the process. For display it depends on the phosphors, the gun voltage and the amount of video memory. For printing it depends on the type of substrate as well as the printing process.

• Highlights may be lost because the voltage is too high on the monitor or the smallest dots are lost either during transfer to the plate or by being worn away.

• Printable tonal ranges can vary from as much as 1- 98% in sheetfed offset to as little as 25-50% in flexo on newsprint.

• The highlight placement is most important both in scanning and in adjusting the gradation.

• For printed output, the lightest point of the original should be mapped according to the lightest value (e.g. smallest dot for halftones, shallowest gravure cell depth or lightest detectable dot in dye sublimation) that can be detected on the output.

• Likewise, the darkest point of the original should be mapped to maximum printable density.

• Intermediate tones can be distributed to emphasize interest areas of the original or control placement of midtones. These can be done using tools in image editing software such as the Image adjust curves feature in Photoshop.