PhotoGrav-mixed results

[Jeff Ring]

Hey to everyone!
I'm new to this forum and to the laser engraving world, but not to the woodworking world. I've recently purchased a Zing 24 40 watt and use Corel X4, PhotoGrav 3.0, Vista 64. I've spent a lot of time learning not only the laser but the computer in general, since wood, glass, and my hands have been my life prior to adding the laser to the tool arsenol. So, here's my dilemma. After opening a photo in Photopaint, converting it to greyscale, cropping it, and resizing it, I export it to a folder and then open it with Photo Grav. Once in PhotoGrav, I select all the settings needed and then final process. The problem is that I've received two different results one in which I can use the tone curve adjustment on and one where I can't. I've looked at the file info on both of the results and can't see any difference. What bugs me is the result I want, the tone curve adjustable one, is the one I can't replicate now! I'd post an image, but when exported as a jpeg they look the same but in Corel they look competely different. Any HELP please? And, THANKS in advance!
Jeff
p.s. Looking forward to getting to know many of you down the road!

[Jeff Ring]

I'll be crawling for a while before I begin to walk!
That being said, is there an easy way to downsize a cdr file to upload it here?

Thanks, Jeff

[Rodne Gold]

Have you actually engraved it and checked the results? If its already processed via Pgrav - there is nothing you can do with it as its a black and white 1 bit image.
Perhaps you are trying to work on the simulation , which will allow manipulation but wont engrave?

[Jeff Ring]

Rodney,
Yes, I've engraved both and had good results. It's just that I had to use brightness and contrast adjustments on one as opposed to just the tone curve on the other. And, what I'm working with are both negative images, so wouldn't a simulation be postive?

[Tim Bateson]

Jeff, Save yourself a lot of time and forget PhotoGrav. You'd be surprised as to the great results you can achieve without it. It's one of those programs that you'll rairly ever have a use for. Some folks here have great results with it. Personally I get equal results with or without it.

[Jeff Ring]

Tim,
If not PhotoGrav, then how would you process a photo portrait to be engraved on clear acrylic using Corel X4?

[Bill Cunningham]

You can check your photograv output from the generated engraving file.
Load it into photopaint
convert it to a grey scale,
resample it down to screen level (75-95 dpi)
and what it looks like on the screen will be pretty close..
If it's for acrylic, you can invert it back to a positive for a look see.. Just don't forget to save it with a different file name. You can't engrave from this file, but it might be useful to see what the difference is between the two files you were looking at..

[Tim Bateson]

Tim,
If not PhotoGrav, then how would you process a photo portrait to be engraved on clear acrylic using Corel X4?

I'm not sure about Zing's driver, but most Epilog drivers have dithering capability. I use Photoshop to enhance contrast, then the Epilog driver's dithering options to do the rest. Works well with either B/W or full color photos

However, I can say, I've never tried puting a photo on acrylic. Lots of graphics, but no photos. I wouldn't think it would be any different from glass or mirrors. In this case I use a dithering that lightens - moves the dots further apart.

[Larry Bratton]

Tim,
If not PhotoGrav, then how would you process a photo portrait to be engraved on clear acrylic using Corel X4?

Import a 200-300dpi photo into Corel Draw.
Edit Bitmap
Convert to Greyscale if not already.
Adjust your contrast to a suitable level in Corel Photopaint. Practice is required to get this right.
Sharpen if needed (Effects/Sharpen/Unsharp Mask) . Usually I push the slider all the way up to 500%, radius of about 5,threshold 2. You may need to experiment a bit here with acrylic.
Image/Convert to 1bit Black and White. I usually use Floyd Steinburg or Jarvis dithering.
Close Photopaint and save, your edited image will then be in Draw.
Send it to the Epilog driver, print it at the same resolution as the photo.
(If I didn't miss a step, you should get a decent result)
I just use the recommended settings provided by Epilog for each material type and print resolution.
(If you are doing a photo on black acrylic or black granite, you will need to go to Image/Transform/Invert) before saving
Watch this video by SMC member Roy Brewer http://www.youtube.com/watch?v=yllZTBA0HO0

[Tim Bateson]

An important thing to remember... Once the photo has been converted to 1 bit - whether from PhotoGrav or other methods such as above... never, NEVER re-size the photo prior to lasering. All sizing has to be to prior to the 1bit processing.

[Dan Hintz]

An addendum to Tim's post...

Post-process resizing is a no-no, but cropping is perfectly acceptable.

[Larry Bratton]

Also, another good thing to do is to look carefully at the 1 bit image. Remember, every black pixel causes the laser to fire. If you see areas that don't look right in so far as having black pixels where they are not supposed to be, make adjustments. I have inverted photos for engraving on black acrylic or granite, checked them, and found for some reason that your going to get something in the area your wanting to be pure black. That can happen with contrast adjustment. If I find this anomaly,I just edit that bitmap and erase the unwanted black dots.
I discovered this one time when I engraved a piece of granite. I felt of the finished piece and I could feel a roughness, although it was not much, it was preventing my granite from being absolutely black where it was supposed to be. I looked at the image and discovered what was happening.