Etch: Color vs Grayscale


#1

I’m doing lots of testing to get a process that’s repeatable, so far it’s very confusing as to how GF determines how deep or dark an etch will be. If I use Inkscape - svg - path - solid colors for a control on Proofgrade maple to keep it simple, how does GF determine how dark the engraved swatches will be?
If I choose SD each time and keep default Speed, Power, Lines per inch, does it ignore the color and look at only the shade of the swatch? Or am I better off using 256 shades of gray and defaults of either SD or HD?
I used a 256 shades of color to engrave a color wheel with a global setting of SD defaults, the closer to a primary color, the lighter it was and then there was a sharp fall off from bright to dark. Tonight I did an engrave with a few color solids, actually had 2 swatches of the exact same rgb color, alpha, opacity, come out 2 entirely different shades, neither swatches were stacked as 2 on top of each other or any overlap, so I don’t see how this is controllable when something like that happens. I want to be able use one of these to control darkness:

  1. Use whatever unique color and use HD for everything and only change speed:
  2. Use 256 shades of gray and use HD with all defaults:
  3. Use unique Inkscape layers, use HD and control with power OR speed:
  4. A mixture of Speed and Power that follows some kind of logic.
    If I can get an in depth explanation of how GF sees a color or shade of gray a a starting point, I can adjust from that. Then maybe I can apply the same method photos. Thanks!
    R.L. Hamm

#2

Someone will point you to a tutorial.

So just a little info… The color within an SVG has nothing to do with the depth or power for a vector operation. It only defines something as a separate operation that you can set the power or speed or select an automatic PG setting.

Engraves of an image file are a little different. There are automatic PG settings where the GF S/W will try to interpret the image as a whole and recreate the image using dithering or variable power to come up with a burned greyscale facsimile. Or you can use the manual settings to try to do so. Kind of complicated to explain in a paragraph. Either way you also need to understand that power and speed affect depth of cut but that does not necessarily translate into darkness and is material dependent. It’s an art if you are not using automatic settings.


#3

I’m really glad you took a shot at explaining that, because I sure as heck wouldn’t want to. :stuck_out_tongue_winking_eye:

The only way I’ve seen to get the “appearance” of different shades of gray is to use dithering. What follows is my personal observations during early testing so they are not official.

There are really only two “colors” available in engraving, burned and unburned.
The only possible difference in darkness comes from charring, burning the wood completely black, and once you get to that stage, there are no shades. But there is a very short drop-off to get to the charred point, so for practical purposes, if you want to achieve a grayscale effect, you have to use dithering, like @rpegg mentioned above.

For the non-pros reading this…Dithering is spacing the burned dots farther apart on light colors, and closer together on dark colors, so that the “appearance” from a distance is of different shades of gray.

The Photo Engrave (raster) function that Glowforge has set up is a dithering program - it looks at a raster image and interprets the spacing on the burned dots to give the appearance of different shades of gray for us. (You can also use other dithering algorithms in programs like Illustrator, Photoshop, GIMP, etc. There are a couple of tutorials on doing your own dithering and halftoning in the Matrix if you like, although I really like the one the Glowforge uses for crisp results, so haven’t really bothered. But here’s the link if desired.)

And while you can over-ride the power and speed settings for your vector engraves to attempt to duplicate what the Photo Engrave setting does for us automatically, it’s a lot of work and the results can be iffy, and can vary quite a bit.

The simple solution if you don’t want to spend all of your time setting up your own settings (and I never have that much time) is to just rasterize your grayscale and use the Photo Engrave setting in the GF interface.

You can make adjustments to the Draft, SD (standard def) and HD (high def) settings to adjust the LPI and change the appearance easily in the interface, so that’s usually what I do. And the Draft setting is 6y, (Demon typed that for you, she’s helping me this morning), the one that I like best for Photo Engrave results. :smile:

Okay, I’d better go feed this kitten before she decides to have me as a snack. ROFL! :rofl:


#4

Ahah! Now those abbreviations make sense.


#5

Yep… much more sense than SD- Stop Dawdling and HD - Hello Danger !:grin:


#6

But that can’t be true, I engraved a color wheel that was an svg image and got quite a few different shades on Proofgrade all with 1 default setting, SD I think it was, the plot thickens!


#7

If you had converted the color wheel to greyscale before uploading it would have come out the same way.


#8

You can do some experimenting with it, but you might want to run a few test patches on whatever material you plan to use, to see what kinds of variances in shade you get by varying the settings.

(I ran a bunch of them, and eventually came to the conclusion that there wasn’t a heck of a lot of variation except between the extremes, so I just let the photo engrave do it’s thing for me…the results give more variation.)

I’ve got some small test strips in this post that don’t take all day to set up. They might be useful if you want to test the engraves on your material:


#9

Thanks for the good info. How do people get depths like this GF logo coaster or whatever it is. THE 3D Engrave
Is this - engrave on high power, sweep ashes out, high power, sweep ashes out etc on the deeper parts?
Thanks


#10

3D Engraving is a different setting that Glowforge offers. If you load a raster image, you have the option of engraving for depth on certain materials like hardwoods, acrylic and the draftboards. (It doesn’t really work on the plywoods since the veneer looks a little wonky when you cut through it into the fill.)

They use an auto-magical algorithm that varies the power and speeds to make darker colors cut deeper, instead of just giving the appearance of being darker.

You need to create a depth map to get good effect with the 3D engrave. (And that is a bit beyond my skills at the moment.) :smile:


#11

There are three settings for engrave:

  • Convert to dots: uses what looks like an error diffusion algorithm to convert shades to dot patterns that are semi-random making the graduations gradual.
  • Convert to patterns: converts shades to defined patterns which leaves a sharper discontinuity between different greys, which might be a good effect for an image.
  • Vary power: varies laser power between the min and max values based on the darkness of the image, in which case the image isn’t made up of dithered dots, but varies the amount of burning of the material. On wood, more burning turns darker, so if you pick the min and max values carefully it can look much better than the other two approaches because the effective detail is much finer. That is, 300 dpi ‘vary power’ can render a 300 dpi image, while a 300 dpi dithered image might only render a 100 dpi image, so it’s much fuzzier.

This is really the same as ‘3D carve’ except that the laser’s power is just enough to char the material, not really burn a depth away.


#12

Thanks,
I’ll check it out, etching a daffodil photo right now with HD defaults.
-=(RH)=-


#13

I’m sorry for my late response. Thanks for the help, everyone!

@rhgrafix Thanks for posting this question. Please post a new topic if you have any others.


#14