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View Full Version : Stochastic 20 plate reader used?


RonYnzunza
03-15-2006, 12:26 AM
What kind of equipment is being used to accurately read plates for stochastic screening?

Is there a special device you need to use to get accurate readings on the plate or paper?

Thanks in advance

epp5
03-15-2006, 04:10 PM
I am told there is a special device to read the plates. I have one ordered right now. (cant remember the name right now) The big thing as I understand is that you have to buy a reader that has the ability to accurately read the Staccato spots on the plate. Not just any plate reader will do it.

ssutton
03-23-2006, 05:53 PM
Ron,

It just so happens that I have been researching this matter as we need to buy a device to read the percent dots on our plates as well. What I know is that there are several types of devices to choose from. For example, Gretag-Macbeth makes a device that uses an LCD camera to take a picture of the dots on your plate an then analyzes that to tell you the percent dot. Plus you get to see what the dots actually look like on plate. From what I have seen, these devices are basically made to read plates (and perhaps printed sheets) and seemed rather expensive to me (in the $3000 range).

I have also looked into something that could be of more use around the plant (something that will not only read percent dot on plate and printed sheet but also read density, hue error, gray balance and trapping) and for that I am looking at a Spectrodensitometer from Xrite. Being a densitometer, it has some limitations when it comes to reading plates (I don't think it it as accurate as say the dedicated plate reader but +/- 1 or 2% is fine for the work we do) but I like the idea of a device I can use for other uses. To me, that makes up for any inaccuracies it might have in reading plate percent dot.

I am attaching (I think anyway. I haven't attached a file using this new this new forum system yet) a PDF that I got from Xrite's website that shows a summary of a GATF study.

I also looked at a device from Beta Color (www.betascreen.com) if you want to see what they have to offer.

Steven

JNeidrich
03-23-2006, 07:49 PM
Depending on what you are doing (print wise and screening wise) a spectrodensitometer may work fine to read plates for dot area, however they have some severe limitations.

Spectrodensitometers are not as accurate as a video dot reader. +\- 2% vs +\-.5%. If this works for you and your shop that is fine as they are very useful tools. For Stochastic I would not expect it to be sufficient.

We have found that the Spectro, since it is measuring the density does not do a good job at judging the overall deviation across a plate (it is best to take your readings in close proximity to where you take your paper and solid measurements). The spectro would show us swings of 4 - 5% across the plate while reading SOLID PATCHES. The same readings when using the video dot reader would only yield a .2% deviation.

Especially with stochastic, your platemaking tolerances need to be tighter than the tolerances you have for the printing process. If your measuring device has more deviation when reading a plate than you are willing to accept on a printed sheet you may as well throw your process control out the window.

Most people will recommend the GretagMacBeth IC Plate II for a video dot reader but I guess it depends on what plates you are running, so check with your plate supplier to see what they recommend.

John

RonYnzunza
03-23-2006, 08:30 PM
Thanks for the info.

I cross posted this question on the Prepress forum since this is the preps forum.

http://www.mygua.org/forums/showthread.php?t=340

It just seems weird that you need a special device to read stochastic plates. I am convincing my boss about this so we'll spend some money and do it right.

I thought density is density (log 10: 1 over reflectance) but with different sensors having different amount of error when reading density because of grain and contrast edges, a diiferent piece of machinery is required.

any ball park costs of devices?