Image challenge- mona lisa onto a VERY small stone

[Darren Null]

It's been quite a good day. My laser actually appears to be doing more-or-less what I want it to with the stuff I've tried, and I managed to burn an image and cut in one operation, which is a step forward. Six bits too. Heh.

So. We wandered over to the beach for a quick drink to celebrate my wife's birthday and to watch the eclipse (the moon popped out from behind the cloud bank 4 minutes after the eclipse had finished....b***ard). Also, while I was there, I picked up some smooth flat stones to have a go at with the laser. My daughter picked up a tiny stone and asked if I could engrave something on it.

"Dunno.", says I, smug from the novel feeling of the laser doing something close to what I wanted it to, "Probably. What would you like?"

"The Mona Lisa".

"Ah".

The conversation developed, as these things do, and pretty soon there was €5 riding on the outcome. Now €5 pocket money is pretty serious money; and my daughter might miss the money too. I think it's possible. My machine does, after all say 1000 dpi in the instructions.

This is the stone. It's igneous:
http://cambs.com/etch/stone.jpg
So I got my calipers out and worked out that at a theoretical 1000 dpi, that'd give me 276 pixels on the long edge of the image of the Mona Lisa (http://cambs.com/etch/mona-lisa.jpg) (218k so linked) that I bagged from Google image search. After some fluffing (consisting mostly of running it through Photoshop's 'photocopy' filter (which has been giving me some encouraging results), I got this:
http://cambs.com/etch/mona-lisa-fluffed.jpg
...which if I can bang down on stone in 1000 dpi should be as accurate a representation as humanly possible with the tools allowed.

I plan to use 100% speed, and gradually ease up on the power. I've flattened the stone on both sides with another stone (and olive oil to polish, to the disgust of my wife), and all is theoretically good.

But I only get one go at it. I'm fairly sure that not many of you have prior experience of the situation, but has anyone had a go at stone for high-resolution? Or stone at all, for that matter? There's probably a reason why this is impossible, but I'm going to try it anyway. Any advice?

[Stephen Beckham]

Darren,

My first thing I would do is remove all the background - everything that small is going to blend together - taking everything outside the hair out might help her stand out.

Other than that - I'm not sure how much the DPI will hold up on such a tiny object and hard object. I usually use 300 DPI when on stone or marbles... That might not support your need for the size of image on the size of object.

My experience has been blow outs when the DPI was that high on stone - the result is a solid white surface where I had pixels and a solid white surface where I didn't....

I guess my next suggestion would be to sneek home a second rock next time... Sorry couldn't help more! Good luck...

[Darren Null]

It didn't work. Coreldraw munged the image up on the way to the laser. Hmmph.

[Frank Corker]

Darren, just on this point, that's a black stone - image needs to be a negative and not a positive

[Dave Jones]

Next time clean the image up a bit more to get rid of a lot of the noise/random pixels in the large open areas. Then in Photoshop convert the image to "Bitmap" mode (1 bit). Use "Diffusion Dither" in that mode change.

Then laser that. DO NOT resize the image after conversion. Be sure it is the correct size before converting to bitmap mode. When you place it in Corel, simply place it. Do not resize it. If it's the wrong size go back to Photoshop and resize it before doing the mode change to bitmap mode.

[Darren Null]

I think it would have worked if corel had passed the image straight on, but I used the 'convert to bitmap' to get rid of the 'image below 300dpi' error message. The convert to bitmap -upon subsequent investigation- turned my lovingly-crafted 1-bit image to greyscale which there just wasn't room for.

I dropped the resolution to 300dpi, to avoid overburning issues and which gave me approximately 1/4 of the mona lisa that I posted earlier and cleaned out some of the more in-yer-face background elements. And inverted the image. Ah well, it'll work next time.

Incidentally, rubbing olive oil onto the slate gave me GREAT contrast, but I don't know whether the olive oil helps the process or just temporarily makes the stone looks darker. I liked the effect so much that I tried olive oil on some other stones. It works, but you have to be careful that your stone doesn't have any little hidden cavities. I got serious blowout with one -obviously more porous- sample.

And rather than use dithering which always looks 'giffy', I'm getting better results with the photocopy and graphic pen (stroke length set to 1) filters in photoshop. True, they both stylise the image somewhat; but you're just not going to get a full-fat bitmap out of a laser printer and I have found the results more pleasing than dithering.

[Dave Jones]

I would consider the photocopy and graphic pen as pre-processing, or image enhancements. But the conversion to diffusion dither, if done correctly, is the final step and will let you engrave exactly what you saw before you converted. It looks bad in the graphics program, but looks great when engraved (again, if done correctly).

The laser burns dots. It's just a matter of letting the printer driver create the dots with it's internal halftone or dithering, or you doing it yourself using a diffusion dither conversion in your paint program or a program like PhotoGrav (which is a dithering program with more direct control over the conversion).

[Darren Null]

I would consider the photocopy and graphic pen as pre-processing, or image enhancements. But the conversion to diffusion dither, if done correctly, is the final step and will let you engrave exactly what you saw before you converted. It looks bad in the graphics program, but looks great when engraved (again, if done correctly).
I agree with you up to a point. And quite possibly the keywords in your sentences are *if done correctly*; which I probably haven't managed yet due to CorelDraw/JPEG difficulties. I have tested every single dithering/rastering combination available to CorelDraw and my laser driver and have been singularly unimpressed with the results so far. And now I'm going to have to test them all again, but with TIFF. *groan*.
So far, all the test burns have come out with massive dots or with a horribly 'giffy' look, like early '90s porn.....*ahem* so i'm told *cough*.

I know I should just buy Photograv, but that isn't an option at this stage of what -for want of a better term- I shall refer to as my career.

So far I've had better end results with the 2 photoshop filters, but that's probably because they're that bit more stylised and translate well to low-poly mediums like glass. Plus, if CorelDraw has been sending nothing but 72dpi to the laser up till now, that would explain a lot.

[Stephen Beckham]

Darren,

I'm not sure if I missed it - but have you tried the RESAMPLE function to get your pictures above the 72 DPI. It's the first step I take on all images when importing from digital camera or the internet. They all come in at 72 and I change them to 300 or 400 depending on what I'm burning...

The thing that bothers me about X3 is when I click on export to save for Photograv - the Export function also has a DPI and Color Mode setting - so no matter what I've got it on the screen, the export GUI has the possibility of changing it again for me...

*** Scratch "has the possibility of changing" and replace with "DOES CHANGE" ***

[Darren Null]

Sorry I'm a bit late answering Stephen. I try to avoid resampling if possible, preferring to RESIZE instead. The difference being that resizing just changes the information about the picture (ie, it's exactly the same, but now it's labelled 300 dpi or whatever, instead of 72dpi). Resampling is just that and may well add another layer of JPEG compression to your image, thus lowering quality.

I don't use X3 for any kind of photo processing, although I expect you can resize in photopaint.

You don't need the very costly photoshop for photo manipulation either. There's the very useful -and free- Irfanview (more of a graphic viewer/swiss army knife, but does do basic image manipulation). I've been using this for years and it's the default image viewer on all my computers:
http://www.irfanview.com/
Or there's this one, also free that has a few effects. Mostly useless for laser engraving, I'll grant you, but the 'find edges' command is pretty competent. And also takes .8bf photoshop filters and there's hundreds of free ones out there.
http://www.vicman.net/vcwphoto/index.htm

[Bill Cunningham]

This is a piece of 'dollar store river rock'. Really just tumble polished marble chips. This one is about 3/4" high and just sent as a grayscale on the Epilog clipart mode @ 400 dpi
The 'Duke' is "right back atcha Pilgrim'

[Darren Null]

That's rather good. And definitely shows what you can do if you have suitable stone. That's (2x2?) dithering. Have you tried one @ 300 dpi (for no overburning) with error diffusion? Should be better definition, but I haven't found anybody selling cheap and pure black marble yet so can't tell you for sure.

I've been trying on unsuitable stone so far; just stuff gathered on the beach:
Slate: I've done a few business cards and with a more-or-less business card sized stone there's just about enough resolution on the thing for a name and a phone number. Still, it's free and seems to impress people. And doing it that way, there's no need to put 'laser engraving' on it. It'd be nice if I could get an email address on there, but no chance on anything pocket-sized. No good for images though, because it has flecks of other stuff in there that scatter black splodges throughout. If you nuke it too hard, you get a 'splashy effect' around lettering.
Sea-polished brick: On the right type (which I'm still trying to find a way of identifying BEFORE I burn it) the lettering comes out a dark green colour with awesome definition. It does rub off very easily though, so no good for anything you're going to carry around in a pocket or want to be weatherproof. I'd dearly love to get hold of this stuff in sheets. On the wrong type, it barely goes a darker shade of orange and sprays dust everywhere.
There's also white quartzy/marbly/granity stuff but that really doesn't work.

All worth a try, but looks very much like I'm going to have to get some sort of polisher and stick to low-res lineart on slate or *gasp, wheeze etc.* BUY some materials.

[Bill Cunningham]

You can buy this "river rock" in Walmart as well as most dollar stores..