View Full Version : Understanding greyscales and colors.

Nick Andraka
03-22-2019, 7:45 AM
Now That I have the Epilog Radius up and running, you all are in trouble,, I will have a million questions.

Typically, when laser cutting/engraving, "red" was cut, Blue was vector etch, and black was raster etch. (from my use of a ULS a few years ago)
The Radius printer driver does allow me to assign "power" and "speed" to individual RGB colors.
And the thickens of the line also determined if it was to go into raster mode or vector.

So if you have a blue line .001, but you turn the "red" parameters up in the printer driver (100% power, 1% speed), would it "cut" ??
Were the Red, Blue, Black colors chosen as design standards? or is there something typically in drivers/firmware that makes each color do a different task.
If I had a black line that was .001, that would really confuse things?

As previously mentioned, I can assign laser parameters to upto 16 RGB colors in the printer driver.
How is greyscale handled in a typical American RF machine?
Does the engravers firmware recognize a "grey" and adjust the laser output? Or does the firmware "dither"?
Reading my machines manual grey scale is mentioned once under "clip art".
Wondering if a job has to be designated as "clip art" to grey scale.

Of course I will be doing a lot of hands on experimenting, just looking for some general theories to get my head wrapped around before doing some trial and error.


Glen Monaghan
03-22-2019, 9:08 AM
I don't know about the older Radius print driver, but newer Epilog drivers have several relevant settings in Printing Preferences. First, on the General tab, you can set the Job Type as Raster, Vector, or Combined (hairlines will vector, everything else will raster). On the Color Mapping tab, you can check Color Mapping to enable setting speed, power, frequency, air assist, and raster/vector modes on a per-color basis. If you don't check Color Mapping, color will not directly control these settings. Finally, on the Advanced tab, there is a "radio button" control called Raster Type where you can choose to do Basic normal rastering, Stamp mode, or 3D mode. Of particular interest here is 3D mode, which sets power on a per-pixel basis to be proportionate to the darkness of each pixel (white pixels get 0 power and progressively darker pixels get progressively more power). If you leave the setting at Basic mode, then colors and gray scales get dithered according to the Raster Setting/Image Dithering choice back on the General tab.

Kev Williams
03-22-2019, 11:28 PM
Always remember that laser engravers are very simple 1-bit \\ on/off \\ 0/1 \\ laser-is-firing/laser-is-not-firing machines. They don't know anything about color. :)

That said-- **In most cases** -- the colors used in a lasers print driver, in your case the 16 RGB colors you have available, are used ONLY as a unique reference, and have nothing whatsoever to do with 'actual' colors. Depending on what you're engraving, you may need several different settings for the same job. Easiest example I can think of, is engraving words in columns. Say you have 6 columns of words, each column has 20 rows of words, which average 2" long overall, and the columns are 3" apart on center... If all the text is colored black, then each LINE of text will be engraved, ALL columns at once. This means each line is engraving approx. 12 linear inches of words, and about 9 linear inches of dead air between them. The time time it takes to 'engrave' all that nothing adds up! To finish the job a whole lot faster, you color the text like this: column 1 BLACK, column 2 GREEN, column 3 BLUE, column 4 YELLOW, column 5 CYAN, and column 6 ORANGE (colors are users choice)-- Depending on machine speed, you'll knock off 20-30% of the time! Other scerario's include mixing raster engraving with vector cutting, or if for example you're engraving wood and want certain engravings deeper than others; each unique color allows you to choose power, speed, number of passes, autofocus or not, air assist or not, raster or vector or both modes, etc etc, specific to that color! -- That's all the driver colors do, and *usually* only applies to vector artwork, anything with toolpath lines. The colors *usually* are NOT used when engraving bitmaps, as in anything with pixels. When engraving bitmaps, the only driver color used for engraving settings is BLACK. When engraving bitmaps, halftone or other varieties of dithering come into play, creating simulated grays by varying the density of black engraving relative to NO engraving. Or as Glen noted, certain machines are capable of per-pixel power management of the laser's firing, which BTW is really cool :D

You mention 'red' as a cutting parameter and line width- With vector art, lines are either "hairline" (or whatever a particular machine calls it), or it's thickened up, which is done in some machine's drivers (sounds like yours does), or you can thicken lines in Corel with it's outline-thickness tool. If the line is hairline, it's can be 'cut' but not rastered... but if it's thickened up even a little bit, the laser and/or driver will consider it 'painted' and it will NOT cut, it will ONLY raster. So usually, should you send a circle to the machine to be cut, but it's been thickened, the laser will simply ignore the cut instruction. Conversely, if you send a circle with a thickened outline to be raster engraved but it's still actually a hairline, the laser will ignore the raster instruction...

Hope this helps a little bit! ;)

Nick Andraka
03-23-2019, 8:44 AM
Thanks for the in depth write up, you have been more than helpful through this whole process.
I understand the colors used in the drawing and assigned in the driver are just labels and have nothing to do with "color"
I did read up on my driver, the order you list the "color" and it's power/speed setting is the order it will be etched. so the column layout using different "colors" will work with my machine, good tip, thanks.

So if I wanted to raster engrave a letter "A" with a darker etched outline (thicker than a vector etch) and a lighter infill, I could set the outline color to "green" and set the printer driver to etch green at a higher power. I could set the infill as yellow and set "yellow" as a lower power in the driver,, that should work.

But, what if when drawing I set the "A"s outline as black, and the infill as a grey,, wonder if the driver/engraver would pick that up without having to set individual power settings in the driver?
Wonder if the black setting in the driver would be a universal adjustment covering black and all grey shades?

Need to get the exhaust system finished and start experimenting.