![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEioMQw7xe-9LQEQRzfLL1X6Vrn_NKuXltcp8BPk-LkEEV7HCUbOynpAdAd24pVgR2vngj4jutzgQQqaLCe-6w4xeGMhG3BxNuhufIiFBtNSKx4WBvE5ef3eNn3Yy3PCTYg1pmttpVwr13E/s400/InDesign+50%25.jpg)
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgeZ-KgYclbrqHTU1SugdyCDrvEegVLPl5TzwChgcYkbXDPqYhk39zSogvFBHjtY_U0RtkiwYHs1meNibaHl3apgFZ4izj1B4p7aZTTy8gGrzUUe0CSxhsU2dHIeOE5hLL4QTmpkV7yyUk/s400/RIP+dots.jpg)
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjo6iicqEnKjZOOo9toxwQ8PX4OTDhQLAR_FOYuZD1qnMcIQ2AUDFhJ0mDC4S2iBNjgPPp3gIZ_tjyRrd6FX5zy55lTIxm4z2qApF6ZTsJBu55ZkUf9I_d3qvhAGzGD9hVruz1hfJnASTo/s400/Dots+on+plate.jpg)
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhrUerIgh33M0QxVXrZTwuaB617LfDTgmT__vbpD87DqKJ5DJMA4WM6uNVdIXsrsAf8vBMzC_FYzpiS_GZQhcIRHb-A26mKdSJo0c2t7tUV_QVMtUfsBsEJ2QXxsU3ZpByJ38uPz3bJC9A/s400/Inked+plate.jpg)
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjijmNjs08RwHVO1d_utnGpscRA2gf-Igeh1BvMD2QPuAnv4XnCqscLWirLWAm3naECxDoOOcheh1LgsDGZlTpBamWxRfYQEIG_H9ysVUXiM4KAEn0I0pNVdTrlRTxKIRM8wIHu1nlCONQ/s400/Dot+on+blanket.jpg)
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4S7ooy-GDLhp6hBCBhK4ijBoHRydDHJZs_PqZrABEOrcLw3_U2r2GlSIwjm9CJ1_saF1jesfX24K-RQEiQQbuYJPBOA03Fswu90JT35jWebSEY9pl637iyMfmFJbyTSq-bR0WbnBHbUw/s400/Ink+on+paper.jpg)
Dot gain is inherently neither good nor bad, it is simply a characteristic of a process that uses pressure to transfer an ink to a substrate.
By convention, total apparent dot gain is an incremental, or add-on, increase in apparent dot area – not a multiplier. For example, 18% dot gain means that the tone value, e.g. 50% on the plate has resulted in a 68% tone value in the final presswork (50% + 18%) rather than 59% (50% x 1.18).
Traditionally, dot gain is used as a process control metric, i.e. for a given tone request there is an expected, target, apparent dot gain value – e.g. for a requested 50% tone the expectation is the presswork will gain 18% resulting in the 50% request measuring 68% on the press sheet. If the target dot gain is not achieved then the print process is examined to determine the cause for failure.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiEX5VKx3J-GWPwJSgnP9lt9OMPtcwXXf5jLp2lVJsBjSchkPks69VLFrMoXTLFX5TrIQceqaWs6d6HfDZ5r9FD_s7hJFEX5Lj6P9_WXczelzZEsDB6Zbd_4EGTGV4P1jcRrfyhM_IkCfw/s400/Input+Output.jpg)
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEge2FIyOWr-lgSaCvPgcle7lF-zsP0xSjNu86pG7h69iWor04CYDh9C52ZwPo7Keqi7QMj_z9J0PvPud2Z4_WqXxrwlvb-ygNyTmWJBYF_NjNprzafRKgfmTWPOURWHFv9GcgRpHSpBxFw/s400/Optica+Mechanical.jpg)
Because of the optical gain component, it is not possible to directly measure dot gain/TVI. The method most commonly used involves using a densitometer to measure and compare a patch of solid ink (100%) to a specified tone patch (e.g. 50%) with the application of a formula to calculate the total apparent dot gain/TVI.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgbm0te-Hij53JRas_wHmA-C-Dyq_23I1ilIQFBcrD2u38nFDWulMILx2bFLUdR9mwwb0AyGgputVOcLfCsivxxiRVW8BpEdr_a2Cd_rv-0i5inl-so3Q1wH-HJFoRlihokFDW6-SRLwz8/s400/Densitometer.jpg)
Historically dot gain/TVI target values for presswork were provided for the 50% tone only. These values, for a 175 lpi halftone screen were: C 20%, M 20%, Y 18%, K 22% at their appropriate solid ink densities. Unfortunately, defining a single tone value as the target for dot gain/TVI does not indicate the actual appearance of the actual presswork.
For example, here is the theoretical print characteristic plotted using only the published 50% dot gain/TVI target values:
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgQL6AiT8Ws8hwQGjOosVAcBznOLTCJqIwK0Gi3-cfXn08-eevKGWIM6KO6k_qq0RqKwbHQlkFxvdFvfVNCVYm-BBnzD41xy8uUoDq2WJKXLKlJ-WOnh19tNlo9lIIUb2Ws5Vsj_rGuXxAd/s400/Theoretical.jpg)
However, measuring and plotting dot gain/TVI at several points through the tone scale defines the "print characteristic" and provides a much more effective appearance-based target for the presswork. Here, based on an actual press run using a 175 lpi AM screen, is the print characteristic targeting the same published 50% dot gain/TVI target values:
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhb7ynUvZM1jNM8TjgCl0-6nAZ5OmI8eEOZkqiWnIUyypxL0ar1L8VR1j0bKr3WnCmGe5JVrBwEBjYdrh3cI2PGZV5ZboN7y2RWDMQplT09hKm3kOK7PcPgcTjufLbd9zvgiNsFrnkjjIj6/s400/Reality.jpg)
In order to achieve better alignment between proofs and presswork as well as presswork from different locations, industry standards and specifications are increasingly adopting appearance-based targets (i.e. a specified print characteristic) for press work. The goal is not to achieve a specific dot gain/TVI at a single tone, but to target the tonal print characteristic irrespective of what dot gains/TVI values are needed to achieve it.
Making the print characteristic the target also enables different screening technologies, such as FM/Stochastic screens that have a different inherent print characteristic, e.g.:
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgreO0o54N7no5tkNU-rjcOrQfOPc9YthgD8f37kS9A5S1e-TxHFJj2_TsWfekYW8u1ksBfbjaJQ2VUG6f3ffyUclMFqct3jj4Wt0JlQe-A-M2Xm3rJo4SXW7lFgaWplStQh5o3xZL7hWA/s400/FM+Dot+gain.jpg)
Dot gain/TVI can provide more than just the print characteristic, it can also reveal issues with ink transfer. In this example, plotting the dot gains through the tone scale:
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhr51Hiu9NlkrxYTrlcJaBYHiwctoh7n_9YxS0n79O2YuyfhxRxeTo0jr3GKXQh9g69XPlb_eZsLrFQ1aTIhHBCiILXqNQ4m9NcVQpGpGH6OuEFRgkECNijJKyrYpUUzmR7Nyo-NY-AwN8/s400/Problem+Dot+gain.jpg)
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgA3n9tCRk5fVB0-9tJb_xgEkX66dM0sGbwUBG8IxTf6HKWPOkBa2Z2yaJc4UjmCMZDuD-0Cptek2KPoXZjhag1VF1Q95qwnyYv_FahC40a7mznOq-62eTROmszyDX76oP1DvB2zgrJXHY/s400/Reality.jpg)
Having a documented standard for dot gain/TVI also helps print production to forensically determine whether a color shift (as in the right side of this image):
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEilu8IhtJwjtINN8NtiKkhH1S0Q1YvDok5cy8yyRVx8zsfeDkopV4wlUPbjgnXDy-_6I2FcDz4bysvtuqI-jwSioWXucNojISi2ol44Wx1S8IWwULf31uyA_HqMMQ_VD9UnCZLcljBHjDQ/s400/krystle.jpg)
Some of the factors that cause dot variations (dot gain/TVI):
Film: mounting, exposure time, vacuum in plate exposure, development time, development chemical condition
CtP: laser exposure integrity, development time, development chemical condition
Printing plate: material wear and tear, dampening solution quantity, pH value, water hardness, temperature, incorrect tone curves
Inking: ink film thickness, consistency, temperature
Printing plate/blanket: packing, type of blanket
Printing substrate: coated, uncoated, surface texture
Presswork: ink transfer, pressure/squeeze, slur, doubling, offsetting, over/under emulsification
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh7r-cg4zJmScr9l8NSN-Qv7C9JKcfxUnalMX94FyTY-zHQYui9d8Vu_csANBHNpyqfpFQFnf4A0E4HYrg0Q6Pr7yQDGi_U994TvHqQiOiuE7qlTbqNEJUOpvPahdOnx0LVV21MsO7bWJ8/s400/Getting+fat+2.jpg)
Below are the historical dot gain/TVI value (and SID) targets for different classes of presswork. These values are based on densitometers set to Status "T" black backing, measured dry.
Sheetfed offset:
Grade 1 & 2 premium gloss coated @ 175 lpi:
C: 1.40/20%, M: 1.50/20, Y: 1.05/18, K: 1.70/22
Grade 1 & 2 premium matte coated @ 175 lpi:
C: 1.30/22%, M: 1.40/22, Y: 1.00/20, K: 1.60/24
Web offset (SWOP):
Grade 3 & 5 coated @ 133 lpi:
C: 1.40/20%, M: 1.50/20, Y: 1.05/18, K: 1.70/22
Newsprint (SNAP):
Coldset @ 85 lpi:
C: .90/30%, M: .90/30, Y: .85/28, K: 1.05/32
Heatset @ 100 lpi:
C: 1.08/32%, M: 1.15/32, Y: .95/30, K: 1.20/35
An excellent post. Appropriately concise and to the point. Good balance between theory and practical application.
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