Laser Engraving True 8bit Shades of Grey

[John Champlain]

I believe that what Jeff, I, and others are working to perfect and improve with our laser diode imaging process might better be described as "continuous-tone" imaging. There are no "dots" or half-toning involved, but rather a smoothly varying shade change between one pixel and the next in an image, aided by the constant velocity (CV) algorithm of the Mach3 CNC control software we use. Each pixel burned by the laser beam is smoothly blended into the following pixel.

Lee is quite correct, in my opinion, that wood does not likely shade evenly in 256 steps from one surface point to the next in response to the degree of power absorbed(?) from the laser beam, but it does appear to shade close enough throughout a complete image so that to the eye it does appear to be doing so. Proving or disproving whether or not wood burns truly proportional to the applied laser power is near impossible with the tools we have available to us today, and is not really debatable with other than personal opinions at this time. A Google search has so far failed to produce any documents relating to the subject.

The diode imaging process also appears to be aided by the spacing of the scan lines of the final images. Currently we are only capable of "scanning" at a step over distance of 0.006 to 0.008 inches due to limitations in the currently available optics we have available to use. The spacing between scan lines (unburned wood) seems to help lighten some images.

We are also generating continuous-tone gray scale images with two different methods, variable power (analog control) and variable feed rate (constant power). The variable feed rate method (VFR) varies the velocity of a fixed power laser beam proportionally to the pixel shades of an image, thus allowing the substrate (wood or whatever) to burn lighter or darker shades. In some instances, I believe the VFR method may be better than the analog method at producing gray shades, depending opon the substrate used, and we have not yet fully explored either method to determine which is best.

This discussion is not intended (never was) to be a debate of which laser imaging method is better/best. What Jeff started out in this thread to show was a different method of reproducing an image with a low cost laser diode. The subsequent discussion has been very informative and enlightening in its entirety, and I believe we have all learned (are learning) a lot about our different methods and the equipment we use. Comparing commercial needs and hobby needs will hopefully not interfere with our future appreciation of each others work and interests.

Thank you all,
John

[Jeff Woodcock]

Well said John!

[Scott Shepherd]

I believe that what Jeff, I, and others are working to perfect and improve with our laser diode imaging process might better be described as "continuous-tone" imaging. There are no "dots" or half-toning involved, but rather a smoothly varying shade change between one pixel and the next in an image, aided by the constant velocity (CV) algorithm of the Mach3 CNC control software we use. Each pixel burned by the laser beam is smoothly blended into the following pixel.

John, that's what many of us have been saying, that CO2 lasers are perfectly capable of doing the exact same thing. It is no "automatic half toning" that happens to every single file. You can take a b/w photo (or color if you wanted) and burning varying shades of gray, all continuous.

My reasoning for not being able to get a lot more detailed about the results from it are based solely on the fact that we learned years ago that it was virtually impossible to make money with, so we've spent little to no time working with it. At trade shows, every laser manufacturer has photos of babies or weddings engraved on stone. It's pitched as a great product. They just don't explain it takes 50 minutes to laser and the average retail person won't spend $75 on a tile. So, in reality, it's driven most people away from experimenting with photos too much.

I feel like I say this in every post (because I don't want you to get the wrong impression of what I'm saying). I think your results are really nice and look great. I still don't understand what you're doing that can't be done on a CO2 laser.

[paul mott]

Steve,

Yes, true 8bit shades of grey engravings (without dithering) can be done with a CO2 laser (see post #79) but I doubt that many will actually try it.

Paul.

[Scott Shepherd]

Paul, I saw that post and it proves what I've been saying from the beginning. I don't understand what it's doing that can't be done with a CO2 laser. I keep getting told it's different, but I have yet to see anything that can't be done with a CO2 laser.

[John Champlain]

Paul, I saw that post and it proves what I've been saying from the beginning. I don't understand what it's doing that can't be done with a CO2 laser. I keep getting told it's different, but I have yet to see anything that can't be done with a CO2 laser.

Hi Scott,
What you say is fully accepted. I don't want to go back through all the previous posts to try and determine how this thread may have turned into a discussion of commercial CO2 vs. hobby laser diode, and it really doesn't matter anyway as that was never the original intent. I think that saying that it (laser diode method) is different can not be arguable, and I certainly will not argue which process is better or worse - it doesn't matter anyway. The two processes are really serving different markets.

What I will say is that Jeff did invent and develop, and continues to perfect, a new method of image reproduction, and his market is the hobby users who want to reproduce images at a lower cost than CO2, and who do not care about the time it takes.

Thanks again,
John

[paul mott]

Paul, I saw that post and it proves what I've been saying from the beginning. I don't understand what it's doing that can't be done with a CO2 laser. I keep getting told it's different, but I have yet to see anything that can't be done with a CO2 laser.

Steve,

I think you are quite correct - commercial CO2 laser machines operating software's have offered exactly this method of image reproduction for many years now - However, if you were prepared to spend just 12 minutes of your time trying it I am certain you would understand why / how Jeff's method is different.

Paul.

[Scott Shepherd]

Paul, what's the 12 minute version? I was prepared to give it a whirl this past weekend, but when you slow the machine to the point where it's in the 1-2% range on things, to get this superfine detail and results of variations of power, it's slower than watching paint dry. I didn't have 2-3 hours to let it (and my exhaust) run to get results. I did engrave a few lines and I didn't see anything I didn't expect to see.

What's the 12 minute version? At 20% speed or 40% speed, you won't see the same thing, as Lee mentions, burning wood at higher speeds isn't going to get you the darker results. You have to use slow speed and low power.

I understand the goal now, to produce a product for people without lasers. That's fine. I thought the hype was from the quality, not the application, and that's what I obviously misunderstood from the beginning.

I still don't see the value at 3 hours of engraving for that small size. I think it's a nobel cause, but if you can do something yourself on a CNC router with a laser diode and it takes 30 hours of run time, or you can sub it to someone with a Vytek and get it done in 3 hours, it would make a lot more sense to sub it out. You'll never compete with something like a Vytek in that market. That's a different discussion, I suppose. I think I'm done trying to understand it, from a business standpoint.

[paul mott]

Steve,

Sorry to keep going round in circles but you made the statement 'I don't understand what it's doing that can't be done with a CO2 laser'.

Jeff posted an 8bit .jpg image earlier, I ran this direct from the image (without dithering) but reduced the overall size to 120mm x 90mm and it took 12 minutes to complete (Post #79 relates).
I don't have a super fast laser, my axis speed was 4500mm/min and the step-over was 0.2mm. OK, my result is not that brilliant but it was just a trial and I am sure that if you are prepared to try it for yourself you would then understand.

You refer to 2 - 3 hours, where does this come from ?

Paul.

[Rodne Gold]

MY laser resolves 256 power levels from greyscale without all manner of external devices and without 1/2 toning..called 3d engraving.
Nothing new , despite the protestations otherwise , it's just re- inventing the wheel in a very clumsy kludgy manner to boot...

[Scott Shepherd]

It comes from an earlier example saying that a 9" x 7" engraving took about 3 hours to engrave.

You can't run the machine fast to get that level of contrast in wood. You have to run it very slow with very low power, which is where the slow times come into play.

[paul mott]

You can't run the machine fast to get that level of contrast in wood. You have to run it very slow with very low power, which is where the slow times come into play.

Steve,

Do you consider an axis speed of 4500mm/min to be fast. ?
Surely, if I can CO2 engrave that image in 12 minutes you can do the same thing. ?

Perhaps I am misunderstanding the capabilities of the commercial laser machines.

(I think the 9" x 7" example taking 3 Hours was relating to diode engraving not CO2).

Paul.

[Jeff Woodcock]

This is how I look at the time it takes to engrave on my machine. First, it's a Hobby, so time is irrelevant. Second, it's paid for so it's not an asset I have to constantly be making a product with to make a profit, or to pay for the machine. Third, it's a CNC machine so it when I start it, I can go and do paying jobs in my shop while it's running, or even go home for the day. It turns off by itself and the engraving will be finished when I get back.

Rodne, that comparison is like comparing go kart racing to NASCAR. Both are a form of racing, but one is just faster then the other and the purse is bigger when you win. I don't think the go kart racers believes there sport is clumsy or kludgy if they come up with new ways to improve there sport. I don't feel what I am doing with the laser diode is either.

[Scott Shepherd]

Paul, correct me if I am wrong, but your sample didn't look like baltic birch. In order to get that dark color in baltic birch, you need to either go fast with a high power, or slow with a low power. If you run it fast with a high power, it skips over a lot of the lighter colors. If you run it really slow, you can get much better contrasts between the light and dark on something like baltic birch plywood.

[paul mott]

Steve,

The wood I used was 3mm Obeche. (I think you are perhaps confusing my work with Jeff's).

Paul.