Problems with rastering; glass & marble

[Darren Null]

I've got my red, green and gold hat on; I've got Bob Marley on the stereo with the bass cranked right up and I have a really huge cigarette, yet I'm still having problems with rastering (on marble and glass).
I've tried the three different types of error diffusion available with the driver; I've tried both photoshop (CS2) and CorelDraw (X3) halftoning and I've tried playing with the speed and power settings, yet I'm not getting the sort of image detail that I *know* the machine is capable of.

Any techniques for getting the perfect image on glass?

[Steven Smith]

IRIE
Do a search for millie, in that thread is an image that really helped me out. You'll see that the graphic doesn't necessarily look good on the computer screen but looks great when processed.
Be prepared for much tweaking of your image. OR you can get photograve and let the software do the work.

[Darren Null]

Tank you for leading I and I out o Babylon!

Now I know what it should look like, I've found that I can get a similar effect by blowing up the image really big (4x intended final size) in Photoshop CS2 and using the graphic pen effect (in the 'sketch' subsection) with a really short stroke (1). It'll take a couple of goes to get the scale precisely right for the laser, but it's pretty nearly a one-touch operation.

Oh yeah. I lookin' at the gates of Zion now...

EDIT: DOH! I'm looking at the image at screen res of 72dpi and the image just needs to be changed to 300dpi. So that's 4.166666666x you need to blow it up if it looks right at 100% on screen. Lucky guess.

[Mike Null]

Is that a plain cigarette you're smoking?

[Darren Null]

Alas, yes.

[Darren Null]

Well, that photograv rendering leaves my revolutionary new 'graphic pen' technique standing. Way smoother, and you get noise with the graphic pen when you really give it some on a large image.

It's not all bad though. I had a go with the graphic pen filter on this image (http://www.noirextreme.com/digital/Earth-Color4096.jpg) (the NASA Earth-Color4096 image- it's 1.8Mb, so I linked to it) and I eventually ended up with this render file (http://cambs.com/etch/Earth-Color4096.zip) (363k). Here's a close up of how it rendered in this close up of Alaska:
http://cambs.com/etch/render.gif
And here's what it looked like burnt onto a bit of packing crate:
http://cambs.com/etch/map.jpg
...and it even semi-rescued a piece of white marble that I didn't dare move and was having problems with. It's a bit manky, I know, but it was just a test burn on a freebie bit of white marble. I didn't spend much time on the graphic initially because I didn't think it would work at all, hence the trouble, but marble is marble and I couldn't just waste it...
http://cambs.com/etch/marble.jpg
12W and white marble. Who'd a thunk it?

[Darren Null]

DOH! All of that and I just found the 'convert image to 1-bit' button in coreldraw. Does the same thing, but better. Mind you, I'm not that impressed with coreldraw...it does things to the image you're viewing so that what you see on screen and what you get as print output are 2 entirely different things.

[Larry Bratton]

Darren:
Turn off color management if you haven't already. It serves no purpose in the engraving process. That may help.

[Darren Null]

Ah. Thank you. It helps considerably.

[Bill Cunningham]

Glass is not really a high res. medium. Photos should be as large as possible for the item being etched.. Without photograv, your not going to get 'really' good results..(no your not going to get a decent photograph on a shot glass even with photograv) You can use photopaint, etc.. to get a good unsharp and edge detect 'then' convert it to 1 bit 'line art' but photograv 'still' works better..

[Darren Null]

I agree Bill- I'm probably going to end up buying Photograv...looked at in detail, Photograv's algorhythm is far superior to anything I've found so far. Mind you, I'm not going to cough up $405 without exploring other options first. I'm getting almost comparable results converting to 1-bit in coreldraw and using the Floyd-Stuckman algorhythm. The image still gets a slight 'giffy' look though.
I seem to recall that there were some good 1-bit converters in a fax program I had once- if I can just remember what it was called.

I'm still finding the edges of what I can do with glass- that aztec calendar file went onto a glass with quite an amazing amount of detail. That was an .eps file though- if I can extract the same detail from bitmaps I'll be happy.

[Bill Cunningham]

If you search around the forum, a few months ago, Rodne posted a very good step by step process for converting gray scales to 1 bit suitable for engraving.. A little more work than photograv, but should work for you better than a 1 bit dither.. And, like anything else, practice 'can' make perfect..

[Darren Null]

I couldn't find Rodne's post- might have been deleted in a board cleanup. Meanwhile, I'm getting quite good results with photoshop's 'photocopy' and 'graphic pen' filters.

[Scott Shepherd]

http://www.sawmillcreek.org/showthread.php?t=59299&highlight=VITAL

[Darren Null]

Thank you. I threw every keyword I could think of in. I even spelt grey, gray.

EDIT: UNSHARP MASK!!! I use that all the time, subtly, to make normal prints come out a bit sharper. It never occured to me to turn it up to 11.

[Scott Shepherd]

I only found it easily because I've hunted for it about a 1/2 dozen times. A printed copy now sits on my desk all the time.

[Larry Bratton]

Darren;
A word of caution on rastering glass. CLEAN YOUR OPTICS OFTEN..especially the focus lens! Glass engraving causes a very fine dust or residue to be deposited on your lens very rapidly. Death to good results. I have been doing some 10x10 pcs and I clean the lens after every 2 pieces.

[Darren Null]

Thanks for the advice. Oddly enough, I discovered that yesterday when I had a 'burning demo glasses' session. Unbelieveable how much cack got onto the lens. I left the air assist on today and that seems to help some.

EDIT: A major step forward came with Rodne's post about "if you want discrete dots, don't go over 300 DPI, otherwise you're overburning details". That explains the silhouettes I'd been getting. If I can stop CorelDraw messing wid me pixels, or if I can get the laser to talk to photoshop, I'll pwn glassware.