Linear colorbar vs. curved colorbar

[roger]

Hi Everyone,

Are there any real disadvantages to running a linear, prescreened 175L color bar (vs. one screened and curved with the live work) other than the fact that it's not EXACTLY representative of the live work that's printing at 20 micron stochastic.

Also, does anyone have experience with the notion that the 175L color bar's dot gain and gray patches might actually show drift quicker than a curved 20 micron colorbar?

Thanks and Fire Away!

Roger

 

[meddington]

HAre there any real disadvantages to running a linear, prescreened 175L color bar (vs. one screened and curved with the live work) other than the fact that it's not EXACTLY representative of the live work that's printing at 20 micron stochastic. ?

More than not giving you accurate information regarding the live image area, a pre-screened colorbar won't won't allow you to confirm the proper Rip compensation is taking place during plating unless you have some other control element. With different screening, curves, gain, graybalance...is there a compelling reason why you would not want a colorbar representative of the live area of the press sheet? I can (sort of) understand the desire for some to see a legacy dot, but I don't follow why you wouldn't want at least the majority of elements representing the actual live area. I can't imagine that this would be an acceptable practice for those undergoing Fogra certification for example. With G7, it's certainly not recommended.

"Also, does anyone have experience with the notion that the 175L color bar's dot gain and gray patches might actually show drift quicker than a curved 20 micron colorbar?"

Aside from showing gray balance shift quicker or not, would it show the shift accurate/in the same direction as the image area?I other words, are you certain a balanced gray patch with linear 175ls screening equates to a balanced curved FM gray patch?

 

[rich apollo]

Aside from showing gray balance shift quicker or not, would it show the shift accurate/in the same direction as the image area?I other words, are you certain a balanced gray patch with linear 175ls screening equates to a balanced curved FM gray patch?

The gray balance information from the color bar would NOT be representative of what was happening on the rest of the sheet.

Long story short - your colorbar needs to utilize the same screening that you are printing.

 

[gordo]

Ink/water requirements for 175 lpi and 20 micron FM are different. If you optimize for your live image area you will compromise your color bar.
The notion of 175 lpi color bar's dot gain and gray patches showing drift quicker than a curved 20 micron colorbar comes from the greater tonal/color stability of 20 micron when SIDs change. 20 micron has a similar stability to the use of heavy GCR in separation. BTW, the same disconnect will occur with 175 lpi colorbar and 175 lpi live image area where the separations have had heavy GCR - for example to reduce ink usage.
That being said, some press side closed loop color systems that use color bar information to adjust ink settings can be confused by an FM screened colorbar since the color and tone reaction when the software makes a SID move does not correlate with what it expects the SID move to achieve.
Don't get me started on gray balance ;-) ( http ://growyourbiz.kodak.com/default.asp?item=2265152 ) LOL

best, gordo
my photos here: Gordon Pritchard's Photography
my sketches here: Sketches by Gordon Pritchard