Image voids when printing on clear acrylic? How to prevent?

[MGB_LE]

We are printing wide format images of vehicles to clear acrylic sheets on an EFI H1625LED. Where there is a headlight reflection or sunlight sparkle in the image, the color value is CMYK 0,0,0,0, or paper white. The problem is that my "paper" is clear acrylic, so the output shows a deletion and you can see through the clear substrate to the wall. I'm certain there's a term for this or a standard practice to handle this challenge when printing, but I'm not sure if there's a term for it.

Another example would be printing an image of a smiling person with bright white teeth on a clear cling film or clear acrylic. Where the teeth are in the file wouldn't have white ink, but an absence of color. What's the common approach to that in prepress, design, or printer settings?

Edit: I removed the part about our printer settings for white ink; I think I was overexplaining and muddying my question.

 

[GaSouthpaw]

Even if there's color, you're going to see through it when it's printed on the acrylic- so how are you addressing that?
Personally, I'd think you'd want the white underbase. Either that, or laminate with white (translucent or opaque, depending on use).

 

[shoresigns]

I don't understand. Why are you printing on clear acrylic if you don't want to see through it? Print on white acrylic. Or if you want the objects in the image to be opaque and the background to be transparent, fill those areas with white ink before printing CMYK.

 

[MGB_LE]

I don't understand. Why are you printing on clear acrylic if you don't want to see through it? Print on white acrylic. Or if you want the objects in the image to be opaque and the background to be transparent, fill those areas with white ink before printing CMYK.

These prints will be mounted to the wall, on standoffs. We print in reverse on the back side of the clear acrylic, so that the client can clean the prints in the future without any damage to the printed surface. That's why we don't print on white acrylic. Our challenge with this job was that it consists of 49 images and we don't have a reliable way to tell all the parts of the image where the color measurement is 0,0,0,0 for CMYK. I wonder if there are best practices for printing on clear substrates so we can avoid these "gotchas."

 

[MGB_LE]

Even if there's color, you're going to see through it when it's printed on the acrylic- so how are you addressing that?
Personally, I'd think you'd want the white underbase. Either that, or laminate with white (translucent or opaque, depending on use).

We are printing three layers: color/white/color to give us the most opacity. However on the lightest areas of the print, there's zero ink coverage, which shows up as an empty space in the print. At first I thought it was a headstrike, before realizing it was the point in the file where there's no ink.

We're looking for a way to spot this potential problem and how to properly correct it. That's why I came to the brain trust. I'm attaching samples of the output to clarify the problem We are printing CMYK+White in reverse on clear acrylic. The "scratched" areas are where the file contains no color, and I don't yet know the best way to spot this BEFORE printing...

 

[myront]

Sounds like a print "mirrored" then laminate then stick to acrylic. Add a white "blockout" vinyl with clear adhesive to the backside of that and trim off the edges.

 

[Chuck Peterson]

You need white behind it. If the wall behind it is white it can in some cases have a nice effect depending on your art. If not, either cover the back with a layer of white vinyl or roll a coat of white compatible paint. Paint on a second surface comes out perfectly smooth however you apply it since you are viewing the surface that is against the acrylic. May sound crazy but it works for me.

 

[myront]

Sounds like a print "mirrored" then laminate then stick to acrylic. Add a white "blockout" vinyl with clear adhesive to the backside of that and trim off the edges.

We don't have white ink.

 

[TrustMoore_TN]

I remember having the exact same issue on an HP FB700- anywhere there were clouds on a sunny day image, we'd get voids like that. My production manager at the time never figured it out. What if you were to print a white flood coat over the whole thing after it prints 2 layers of color. Seems like you would get the saturation you're looking for and the flood coat would fill in the voids. Granted, I'm not as versed on how to set this up, but it might be something to try.

 

[ChrisN]

What white ink print options do you have? Our CET has a number of options, but the relevant options here are "Middle Layer" and "Middle Layer of Image". Basically, "Middle Layer" prints color/white/color with white behind the entire print job area - even margins, cutter registration marks, etc. However, "Middle Layer of Image" prints a dot of white wherever a dot of color is in the image. So if the image fades to white, the white ink will not print since there is no color (White in CMYK is 0,0,0,0). It sounds to me like your white print mode is something similar to the "Middle Layer of Image" on our printer.

 

[MGB_LE]

How we are addressing it for the time being is to have the printer flood white across the bounding box, so that the voids are filled with white, but that uses more ink than I'd like.

One thing we will do going forward in prepress for clear substrates is the following process in Photoshop:

Select|Color Range,then choose the problem area|Create a layer from that selected area, and fill it with 1% black, 1%cyan, or anything that adds color to the empty area.

Our EFI printer has a white printing option called "Inked Area" which means that it will apply white ink behind any area where there's print. So even having a 1% coverage on these blank areas will allow the printer to print white behind it for extra opacity.

I appreciate any feedback.

 

[MGB_LE]

What white ink print options do you have? Our CET has a number of options, but the relevant options here are "Middle Layer" and "Middle Layer of Image". Basically, "Middle Layer" prints color/white/color with white behind the entire print job area - even margins, cutter registration marks, etc. However, "Middle Layer of Image" prints a dot of white wherever a dot of color is in the image. So if the image fades to white, the white ink will not print since there is no color (White in CMYK is 0,0,0,0). It sounds to me like your white print mode is something similar to the "Middle Layer of Image" on our printer.

This time we are using Bounding box. Typically we would use Inked image to conserve ink, except the 0,0,0,0 problem. In answering your questions about our white ink options, I have just learned that perhaps I need to use White_Inverse, which is an option I didn't realize/remember that we had. Sometimes talking out the problem helps. Thanks folks!

White channel Spot color WHITE_INK: The spot color that is defined as WHITE_INK in the document. Any color separation from the job that is mapped to WHITE_INK and saved as a spot color table (*.cxf). The spot color table must be selected on the Spot Colors pane. The spot color WHITE_INK is output without color management in Fiery XF.

Inked image: A white ink dot is created for all pixel information that is not 0,0,0,0,0 (including Spot color WHITE_INK). You can exclude WHITE_INK from the print job on the Spot Colors pane.

Bounding box: All image pixels are printed in white ink. This is the recommended setting for creating a base linearization file.

White_INVERSE: A white ink dot is created for all pixel information that is 0,0,0,0. You can exclude WHITE_INK from the print job on the Spot Colors pane.

Ink chroma map: Additional white ink is applied to light areas. White ink is reduced in darker areas to save white ink.

Off: White is not printed, even if there is an appropriate color separation.

 

[MGB_LE]

What white ink print options do you have? Our CET has a number of options, but the relevant options here are "Middle Layer" and "Middle Layer of Image". Basically, "Middle Layer" prints color/white/color with white behind the entire print job area - even margins, cutter registration marks, etc. However, "Middle Layer of Image" prints a dot of white wherever a dot of color is in the image. So if the image fades to white, the white ink will not print since there is no color (White in CMYK is 0,0,0,0). It sounds to me like your white print mode is something similar to the "Middle Layer of Image" on our printer.

ChrisN, asking that question forced me to go back and research more diligently, and I think the White_INVERSE option that I discovered is what would've solved my problem. I'm not going to change form Bounding Box for the project we're currently printing, but I'll be smarter for the next time a similar job comes up. Yes, your "Middle Layer of Image" option is similar to our Inked area, and we choke the white just a hair so that it's never visible.

 

[ChrisN]

ChrisN, asking that question forced me to go back and research more diligently, and I think the White_INVERSE option that I discovered is what would've solved my problem. I'm not going to change form Bounding Box for the project we're currently printing, but I'll be smarter for the next time a similar job comes up. Yes, your "Middle Layer of Image" option is similar to our Inked area, and we choke the white just a hair so that it's never visible.

Going by your description of "White_INVERSE", I think you'll end up with the exact opposite of what you are getting now - white ink only where there is no color ink. It looks like "Bounding Box" is your best bet out of the options you list, without creating a spot color.

 

[Stella_FB700]

I just print my acrylic (clear) at MAX DPI Saturated _ Custom ICC profile - 350% ink limit.
And the adhesion is golden.

Just an FYI

 

[Bly]

I know in Onyx there's an eyedropper tool in spot colour settings you can pick the clear areas to print white.

 

[Pauly]

Woah Woah Woah.
Slow down guys. Lets handle this properly.

Im assuming you're using the EFI H1625 LED listed in your name for printing on the acrylic?
Ok let's assume that.

It has White ink - Good.

To have an understanding on how printing works, anything to do with putting ink or paint or pigments on a material is Subtractive meaning you're started with a white (for example) base and removing light by adding colours of ink to the sheet to create other colours. You can only go as bright as your material and as white as your material. Sp essentially you need white to get a big range of colours. That's why all the media you print on is white.

Now Acrylic is clear, No white on it. When you print on it with out any white ink, the colours will be wrong and opaque because there's no white. You need to FLOOD FILL the print so it will flood it with white ink so it looks like the way it should.

No printer will recognise the 0/0/0/0 as white to print white ink. Because to a printer, Or really the ICC profile, 0/0/0/0 is the colour of the media you're printing on which usually is already white.

You can set 0/0/0/0 in your rip to print white ink as a "Spot" colour but it will only print white on 0/0/0/0 sections. Anything with 0/0/1/0 for example will still have no white and will be opaque.

So a proper answer - Yes you need to flood fill white on your print.