Flexo: Removing 1% dots in Photoshop

[christod]

We frequently have need to deal with 1% dots in Photoshop images, when preparing the images for flexo printing. In our workflow 2% dots print just fine, but 1% dots can 'dirty-up' on the printing and end up looking far darker and nastier than a 2% dot. (This is most often a problem with the black channel.)
A very common work around is to run a 'minimum dot' curve, making 2% the minimum in the file. This is only so-so OK, as that 2% on file actually prints 10-12% on the print, due to various factors. In consequence the image highlights noticeably 'grey up.' So we would like in some case to be able to eliminate the 1% dots entirely, rather than boosting them to 2%.
The problem is we have not found a satisfactory way to eliminate the 1%s in the images, without also making the current 2%s in file into 1%s. We typically use a curve to do this adjustment and, as stated, we end up with an unsatisfactory result.
Can anyone offer any suggestions?

[gordo]

The problem is we have not found a satisfactory way to eliminate the 1%s in the images, without also making the current 2%s in file into 1%s. We typically use a curve to do this adjustment and, as stated, we end up with an unsatisfactory result.
Can anyone offer any suggestions?

Rather than use a curve, try clipping in PShop using the pencil tool like this:


I clipped at 2% for clarity, but you could clip at 1% if you prefer.

best, gordon p

[christod]

Thanks, Gord.

Please try it again as my browser is not allowing through the image you are using to show your suggestion.

Are you suggesting the pencil tool in the curves dialogue?

If so, this is where we have been trying to eliminate the 1%s but also bringing down the 2%s to 1%, therefore not solving our problem.

Thanks for your thoughts on this i will try anything you suggest.

[Kevin@Kodak]

Thanks, Gord.

Please try it again as my browser is not allowing through the image you are using to show your suggestion.

Are you suggesting the pencil tool in the curves dialogue?

If so, this is where we have been trying to eliminate the 1%s but also bringing down the 2%s to 1%, therefore not solving our problem.

Thanks for your thoughts on this i will try anything you suggest.

This is normally known as a "bump curve" in flexo printing, and is quite common because of the difficulty in holding clean highlight dots. I'm actually impressed you can hold 2% - often this is more like 4-5% in the flexo world.

There's another way in Photoshop to do this - esentially remapping your whole image to go from 0-250 (or whatever level you can hold on press) instead of 0-255, but the trick would be to leave pure white as pure white (instead of dirtying it up too).

The best suggestion I would have is to remap the image to 0-251 (to bring your 1% down to 2%), then to keep your highlights clean do a selective replacement of everything at 251 to 255.

1) Image/Adjust/Levels - set the Output Level maximum to 251 (i.e. 98% + 1)

2) on each channel in the image, select by value (anything 251 or higher - probably easiest with Select/Color Range and eyedropper on a known area of 251 with 0 fuzziness?) and replace it with 255 by cutting/filling/whatever.

You could probably do most of that with Actions too.

Just my $0.02 - there may be an easier way to do the second part, but I'm still working on an ancient version of Photoshop (I was a certified instructor for PS4, but I haven't kept up).


(to get a Kodak plug into this, check out our Flexcel NX system - it can hold those 1% dots cleanly, and even do 300lpi and FM work due to it's flat-topped and stable dot structure)

Kevin.

[Flexo Grunt]

I rarely do an overall curve on a image. With every image, I usually will go through each channel, evaluating how it will likely print and will mask out areas I would like to change and apply a curve to just that area on that channel(s). Very often I will eliminate a 1%-5% dot on 1 or more seps that will dirty up the print and usually I will not add dot to the black channel because dropping to 0% in an image rarely causes a problem. (depending where it ends)

[gordo]

Are you suggesting the pencil tool in the curves dialogue?

If so, this is where we have been trying to eliminate the 1%s but also bringing down the 2%s to 1%, therefore not solving our problem.

Yes. But something must be wrong. So I created a greyscale PShop image with 1%, 2%, 3%, and 4% patches.
I then used the pencil tool in the curves dialog box to remap 2% to 0%. Below is the result. At top is the original and below the line is the image remapped.:



Here's the URL if the embed doesn't work:
http://i338.photobucket.com/albums/n...pedpercent.jpg

As you can see (and measure with the "show info" tool) it remaps correctly. 2% and 1% have been hacked off and are now 0%. 3% and 4% are untouched they're still 3% and 4% respectively. I tried this with a CMYK image and it worked there as well.

Download this image and try it yourself. When you use the pencil tool click on the lower corner of the curve and drag to the right until you get the input/output values you want. Don't enter the % values manually.

BTW is the URL to the image in my previous post:

http://i338.photobucket.com/albums/n...d/Curves-2.jpg

Let us know if that works.

best, gordon p

[christod]

Thanks, Gordo.

I am still trying to get to your uploaded images. They are being blocked by corporate IT policy. I have asked IT to unblock them but that hasn't happened as of yet.

[christod]

Ok, got it.

Thanks again, Gordo.

I wasn't using the pencil properly: you need to locate the percentage you wish to eliminate, then draw down, and then draw over to the left, to 0%. I was missing that last step and therefore not accomplishing very much.

I found eliminating the 2% on the black worked best. I still needed to go through the black channel visually and lasso out some remaining 1% tone.

Image looks much better (or at least it will when printed).

Thanks for your screen grabs. They helped me grasp that last draw to 0%.

[gordo]

Thanks for your screen grabs. They helped me grasp that last draw to 0%.

Tell that to your IT people and maybe they'll trust you to look a pictures on your screen - at least from PrintPlanet. :-(


best, gordon p

[jlee]

Esko Artwork has a tool that is pretty quick for this, it's called Flexo Perfection. It very easily removes the scum dot you are referring too (scum dot from a flexo perspective is this 1% where the litho guys have scum from water issues). They also have something called deskpack for Photoshop that does very similar things. I believe that these are available for a free 30 day trial from their website.

Hope that helps,
JL