Halftone, how to make

[John Ada]

Have a solid colored(4), vector logo, that needs to be engraved on acrylic.
Have seen or heard to do at about ( laser 25 w mini ) 300-400dpi. but what is the best way to make it into a halftone so it looks great, with maximum contrast. Some parts of logo are rather small, other big and solid fill.

Thank you.

[Larry Bratton]

John;
All images that are engraved are dithered, black and white images regardless of how they start out. You say your machine is a "25w mini". Is that an Epilog machine? If so, a choice of dithering patterns are available via the Epilog Dashboard driver. Good quality can only be obtained if it is a good high quality image of 300dpi or more. It should be engraved using the same setting in the machine driver as the image's actual dpi.

[Mike Null]

Can you post a picture of the logo? If not, then just experiment with the various options within your driver to test the results.

If you are not satisfied with that then you can use your drawing program to alter the image. It would be helpful to know what kind of software you're using.

[Dan Hintz]

To clarify Larry's post...

He means the base image should be at least 300 dpi for a quality engraving, whereas I believe you were talking about engraving at 300-400dpi.

To answer your question (in a manner of speaking), the drivers usually do a decent job at converting a color to a dither pattern that represents the eye's view of which color is darker (and therefore places a more dense halftone in that area). But not always, so sometimes it pays to tweak the colors before printing. You'll have to experiment if that's the case, but you'll probably be happy with what the driver does for you.

[John Ada]

Yes, Epilog ; Using corel x3 and x5. Can't post. img, however it is in eps vector format, should I convert all color to b/w then print to laser? Thanks

[Richard Rumancik]

John, off the top of my head, I'd probably use grayscale fills instead of colors. Make a copy of the vector image, then convert it to bitmap (grayscale). You can start with 300 dpi but if you need more quality you could try 400 or 500 etc. Open/edit in PhotoPaint and convert it to b/w for lasering. It will ask what mode - halftone, line art, ordered, Stuki, Jarvis, etc. Personally I would not use halftone as it does not look good to my eye. I tend to use Stuki but Jarvis and Floyd are similar. You can play with Intensity setting and with the actual gray fills used.

Plot at what ever resolution you used in the conversion to bitmap.

I think this would give you more control of the outcome. The screen preview of the b/w bitmap might look odd at first if you have not done this but you need to get a feel for screen view vs. output. Then you will have a good idea of how it will engrave.

[Larry Bratton]

John:
OK. That being said. You have Corel Photopaint. If it is a good quality image of 300dpi (base quality as Dan said), from the Corel Draw screen, activate Edit Bitmap and your image will open in PP. You can, if you like, change it to 8bit greyscale and possibly adjust the contrast or other adjustments. Open completion, if you elect to do that step, convert it to Black and White 1 bit.(otherwise you can convert to 1bit without converting to gs) You will have the option to select Halftone etc on the drop down. I use Floyd Steinburg mostly for photos, one of the others, Jarvis or Stucki. When you finish, close PP and it will ask if you want to save, answer yes and it will put the resulting image back into the Corel Draw screen. Engrave it without enlarging it or anything, be sure and use the setting for the dpi in the driver to match the base image.
(Edit) Also, your acrylic settings are pretty much like the Epilog manual shows them. If you are using clear acrylic, it needs to be cast material in order to get a nice pleasing frosty mark.

Ooops..I assumed it was a bitmap. If vector, probably just send it straight to the laser and use the dithering options in the driver. Standard is the default and it would probably be fine.

[John Ada]

Well, tried all colors to b/w varying amount of black 10 to 50%, output at 300 dpi, dots too small, would like a bit larger and more space between them, How might I achieve that? Thanks

[Dan Hintz]

Only way I can think of offhand is to make the screen a 1-bit color first, followed by a filter for increasing the granularity. I'll think on it some more when time permits...

[Richard Rumancik]

Well, tried all colors to b/w varying amount of black 10 to 50%, output at 300 dpi, dots too small, would like a bit larger and more space between them, How might I achieve that? Thanks

John, quite honestly I can't follow what you have tried here and what the problem is. (What do you mean, dots too small? What exactly are you looking at?) If you can elaborate you might get more responses.

[Larry Bratton]

John:
I agree with Richard. I thought I knew what you were asking, but with your comment about the dots being too small I am not sure. If you could tell us what the steps are that you are taking in your process we might could get some insight into where you are trying to go.

[Michael Hunter]

Are the "dots too small" because you want it to look like an old newspaper photo?

If so, try this -

From Corel, go to edit the bitmap in PhotoPaint.
Resample down to 72dpi or less (you may need to experiment here)
Select Convert to 1-bit B/W and choose halftone "fixed" 4x4 (or 8x8) with a coarse screen (I tried 1mm)

Now you have a choice - either resample back to 300dpi before exiting PhotoPaint, or, just exit.
If you just exit, then resize (by stretching it) the picture in Corel and let Corel sort it out when it is printed.

The above will give a simulation of the "blocky" look of old newspapers, but won't give the "round blob" effect.
It is possible that other editors (Photoshop, Paintshop etc.) may have an option for the round blobs - if you have any of these give them a try.

LOTS of experimenting to do! - which is why I generally stay away from photos.

[Mike Null]

I think I'd start over from the beginning. Ungroup your drawing, change your color fill to varying shades of black as Richard suggested and engrave it. By varying the percentage of black your driver will compensate and produce the differentiation you want.

If that doesn't work experiment with using the post script color fill tool which will allow you to control all elements of the fill.

[John Ada]

Got the job finished, I was not too happy with final, but client was happy. I guess I'll have to run additional samples to try to refine for next time. Any additional thoughts are appreciated. Thanks to all who replied!

[Richard Rumancik]

John, you'll have to spend the time to indicate exactly what you tried and what the result was. Maybe take a few photos as well. People here are willing to help if they understand the problem. At the moment, we are speculating on what the issue is and giving solutions but may be addressing the wrong problem.

[Mike Null]

Come on John, a number of people took the time to offer suggestions. Let us know what you did.

[John Ada]

Thank you again to all who replied. I basically did what Richard suggested, grayscale fill instead of color, convert to 300 dpi, On Epilog mini I downloaded a newer driver which has a (brighten) mode which helped. As time becomes available I plan to do more testing. Thank you Again.