What’s the largest image size ( w x h x resolution) you can raster for lasering? If you use an image with a low resolution but large dimensions, how will that be rendered by the cnc?
That’s a really interesting question and one that I bet @jjneeb would know!
That is an interesting question. I have never explored how big of an image the plugin can hold. There isn’t any rendering or modification done by the plugin. It simply loads the bitmap array into memory and runs it. From the header of the .bmp it knows the image and row pixel counts, and also the dpi value. Its up to the user (like all laser SW I know of), to prepare the image itself to have the proper dpi to match the acutal width of your laser spot. The dpi will be translated into the pixel width to manage when it fires each pixel, and the Y axis step size when moving to a new line.
I’ll ask the developers if there are any limits to the array size.
Which memory? The smoothstepper board memory or the computer running mach4?
So as DPI goes down, the diameter of the laser spot will go up?
Computer memory. I sent a note to the Warp9 experts to see what the array size limitations are. I have done stuff up to about 1200 pixels in each direction, but I’m sure its a lot bigger than that.
Laser rastering is almost an art. There are a couple of really good FB pages that are dedicated to it if you are interested (Den of Lasers, Laser World, Free Laser Engraving Files). They have a lot of processes documented, different techniques, etc. And you can really see some amazing things done with lasers. Some of them look like the photograph original (that requires a very fine spot size like from the Opt XT-50, but with the 15W you can do that, it will just have to be on a bigger picture size).
The basic process is to figure out what you laser’s spot size is approximately with some sample burns. Every power setting, feed rate, and material type will give you a different diameter due to the gausian power distribution of a laser beam (much higher in the middle than the edges).
After you get a starting beam spot diameter, the inverse of that is your starting DPI. Now you process your picture (with something like ImageR, or GIMP) to covert to the size, DPI, grayscale/dithering, contrast and brightness, etc. etc. that you want.
Then you raster that image and see how it turns out.
The people who do the really exceptional stuff will run the same image at several different DPI values to see what looks best, so this means creating a new file for each DPI value.
So you can see this is pretty intensive. Once you get the feel for your laser and the material, its less trial and error because you have a pretty good starting point figured out after a bit of practice.
This is why if I am doing any kind of sign, or logo, or anything that I can create in vector form rather than a picture image, I will always do that because I can make a logo in Vcarve very quickly and make an assumption on power and feed rate based on experience and almost always get it right the first time. I only do rastering if I’m making a true picture image.
Here is a link for some good laser impage processing tips: https://www.youtube.com/@ImagR-Laser
This features the ImagR software (which is great and a pretty good price), but the process is the same if you use something free like GIMP (just as capable, but maybe not quite as user friendly).
This is good Info, thanks. And I sent requests to the Facebook groups you mentioned. Thank you.
In the past I had been writing various CLI image processors in python & the occasional inkscape plugin, but those output to gcode, which I’m sure you understand Is impractical at any size larger than I was working at the time:
Now that I have a large AVID CNC I’m very interested in exploring outputting to more capable formats like bitmap or binary so that I can burn larger, lower res or mixed res VERY large format images. Like take a photoshop document and write an action to export the layers as .pngs then have a script create burning profiles for each exported layer.
With the rastering, its gonna just be as much memory as can be allocated to store the pixel array. We’re gonna test it to see if we can break it 
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Ok, i did a little experimenting. I could load and run a 10k x 7529 pixel image ok. That file is 220MB in size. I did not run to completion because at 100ipm that would take about 28 hours (ya, thats a dang big image.
I made two of them even bigger, both over 400MB, and they blew up Mach4 (hard crash). This is a known issue if you run out of memory with Mach4 (but its almost impossible to do with any normal Gcode execution).
Anyway, so you can make a 125dpi image 7 feet wide yet if you want to. Warp9 is going to fix the plugin so it at least recognizes a .bmp that is too big and will refuse to load it.
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