Laser Engraving True 8bit Shades of Grey

[paul mott]

Jeff,

I still remember first seeing your work last summer and being totally amazed. My initial thoughts were that it could not be reproduced with a CO2 laser for many of the reasons that others have mentioned in this thread.

Together with my big brother (Mr.T) we set out to try and it was not an easy road. John may recall seeing some pictures of the early attempts where we were cutting 4mm deep into the MDF in the darker areas of the work before we got the balance between speed and power on track. This is one of those areas where practice makes perfect but, of course, we never ever reach the perfection but there is always improvement as we continue to learn.

Just a generalisation but it appears that all commercial CO2 laser machines are capable of producing true 8bit shades of grey (without dithering) but it seems that none actually do (perhaps with the exception of the machine manufacturers sales literature photo’s).

Keep up the good work my friend.

Paul.

[Rodne Gold]

Just a generalisation but it appears that all commercial CO2 laser machines are capable of producing true 8bit shades of grey (without dithering) but it seems that none actually do (perhaps with the exception of the machine manufacturers sales literature photo’s).

Paul the reason most of them don't offer that option for photo engraving is that most substrates are 1 bit and it would be useless for them ... and those that can resolves "shades" are way to fiddly to work with and get it just right..

[Scott Shepherd]

Steve,

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

Paul.

Paul, I'm not confusing the two. He posted photos done in Baltic Birch. You posted a photo showing it done in some non-baltic birch product. He said to burn the baltic birch, it took 3 hours (actually closer to 6, he ran it twice), but he said he can do it in 1 pass if needed. So I took 3 hours. I said your photo took less time because it was done in a wood that burns a lot darker than baltic birch. My comments about time were based on trying to replicate exactly what he posted, not simply engrave the same photo on something that works better than the substrate he specified.

So no confusion on my part, but I probably didn't explain it well enough on who/what/where I was referring to. Sorry about that.

[Jeff Woodcock]

Thanks Paul,

I use the cabinet grade Birch Ply. only because I got it cheap and I have a stack of it. The hardest part of this engraving process is, cutting it up into usable pieces.

[Lee DeRaud]

Do you consider an axis speed of 4500mm/min to be fast. ?

That's ~175ipm. ISTR Jeff's CNC machine was operating at 20ipm, so yeah, for the purposes of Steve's explanation, that's "fast". But most of the commercial CO2 machines will raster upwards of 1000ipm, so it's also "slow"...context is everything.

One last thing before I leave...

The whole premise of this thread is "Dithering is bad." But it's not: it removes the grossly inadequate material tonal response from the equation. Laser off equals pure "white" (to the full capabilities of the substrate), and usually you can obtain pure "black" over a rather wide range of laser power. You're not diddling around trying to match a rather narrow and nonlinear tonal response curve to the tonal range of your input image.

Think about this: have you EVER seen a photo "printed" by a laser engraver (CO2 or diode) that has as wide and smooth a tonal range as the output of a simple $100 monochrome laser printer? I think not.

[Jeff Woodcock]

Lee, if your talking about me, I run mine at between 40-60IPM depending. Feedrate effects how dark or light I want it. Most the time I run at 50IPM. My new build on my servo router should be able to engrave between 150-200IPM with the increased power of my laser diodes.

Also, you are the first one here to say dithering is bad. No one ever said that anywhere I have read in this thread. I do use dithering on harder to burn materials also. It's either full power or none. I even posted an engraving in this thread that I dithered the image and engraved it by pulsing my laser diode. The Birch Ply. had white wash pickling stain on it which makes it harder to burn. I have a few different options my machine can engrave with.

I'm still trying to figure out who Steve is.

[Scott Shepherd]

I'm still trying to figure out who Steve is.

Read my signature

[Jeff Woodcock]

I have been so busy reading the posts, I never did read that.

[paul mott]

Just a generalisation but it appears that all commercial CO2 laser machines are capable of producing true 8bit shades of grey (without dithering) but it seems that none actually do (perhaps with the exception of the machine manufacturers sales literature photo’s).

Paul the reason most of them don't offer that option for photo engraving is that most substrates are 1 bit and it would be useless for them ... and those that can resolves "shades" are way to fiddly to work with and get it just right..

Rodney,

I think you are absolutely right. As far as CO2 lasers are concerned most substrates are treated as being 1bit.

I may be wrong (and I stand to be corrected) but I think the reason Jeff started this thread was to educate us all to the fact that some substrates will handle 8bit resolution. I accept that it may be fiddly to set-up and the process is not for everybody but I am all for learning anything that I cannot already do. One day the additional knowledge may come in handy.

Paul.

[Jeff Woodcock]

Thanks Jeff, I missed that link to the photo. I've downloaded it and I'll give it a try when I get a chance.

Scott,

You have not had a chance to try it yet?

I requested a new function to the image to gcode program I use to ignore any areas where the background has been cut out or if there is any larger pure white areas when using the analog modulation settings. Before it would only do this when using TTL modulation with a dithered B&W image. The author did some reprogramming to his software and now the laser will not run in any of those areas to save on engraving time. This is the same image I engraved before and I did it in one pass this time at 50IPM. It is the same size as the engraving I posted before and it cut down 36 minutes off the first pass engraving time that was set at the same feedrate.

[paul mott]

Jeff, nice work. Just out of curiosity you say that you reduced the job time by not scanning the background.
Did you have to Photochop the artwork (from Post #44) or did you software reduce the bit depth to achieve this ?

Paul.

[Jeff Woodcock]

Thanks Paul,

I just used Corel Photo Paint's Magic Selection Wand to select the background and then cut it out. It was easy to select when the background was all one color in the original image. When saving the image file, Corel will make that cut out background area pure white. This area being white when brought into PEP4PL, it will just ignore those areas now when generating the gcode. My settings were the same as before with the .007" pixel resolution and the feedrate. The laser beams path just went back and forth to the edge of the image instead and it just ignored the background area and that is how it saved on the engraving time.

Jeff