I’m new to vector graphics and the Glowforge, so potentially stupid question, but am I missing something with available resolution in the GFUI?
I can export a .PNG from Inkscape and am able to set the size and DPI, however when I upload .PNG files to the GFUI, they seem to automatically scale to ~ 90 DPI (for instance, a 4" x 4" / 300 DPI image displays as 13.3" x 13.3" on the GFUI - I don’t know how to view the resolution, but I presume it’s now ~ 90 DPI). Alternatively, I can scale my image within Inkscape to 4" x 4", but this automatically reduces the resolution to 90 DPI. When I save as an .SVG, the image is now only 360 x 360 pixels instead of 1200 x 1200. When I upload the .SVG to the GFUI, the size is now correct (4" x 4"), but my resolution can only be 90 DPI. Is this just a limitation of Inkscape’s .SVG format? Am I just doing something wrong?
I’ve found what appear to be threads where folks are comparing the output from files of different resolutions. Are these all created in Illustrator? Any help or guidance folks can offer would be greatly appreciated!
You’ll want to update your Inkscape program. The older version had an output DPI of 90. The current one has an output DPI of 96 and that is the same one that Glowforge assumes for input.
Thanks for the suggestion, but I think my bigger question was how does anyone get a resolution higher than 90 or 96 DPI? If the machine can print at several hundred LPI, shouldn’t it be possible to upload something with a higher resolution?
I’ve never experienced the issue you describe. I am currently printing an image with far higher DPI than Inkscape or the Glowforge UI need. Inkscape doesn’t reduce the resolution. I am engraving at 675lpi (which would be the vertical/Y-axis DPI)…
Perhaps I downloaded Inkscape from a bad repository? How did you set the resolution in Inkscape? I’ve tried adjusting all three variables (screen, print, and import) in Edit -> Preferences, but it hasn’t changed my .SVG output. Thanks for any suggestions…
Good question…you’re confusing PPI with DPI and LPI, and a lot of people do.
This is my understanding of what’s going on…
DPI (dots per inch) is used to assign a fixed size to the diagram, because the SVG file type is basically unitless. Each design or drawing program has it’s own convention, and the GFUI will convert a file type from that program to the correct size, based on the normal export DPI for that software. It converts the normally expected results to match the 96 DPI input that the Glowforge interface uses. Problems can pop up when it gets something unexpected, so either update your Inkscape program or set the import and output DPI to 96. (Edit> Preferences>Bitmaps tab> Default Export Resolution = 96 dpi)
PPI (pixels per inch) is the usual measurement in raster images. The higher the PPI, the more refined a printed photograph will appear to be, because the dots of ink are smaller. Since more people are familiar with PPI, they think that a higher value will lead to a better image. That doesn’t always hold with laser work, but you can specify a certain PPI for raster images in excess of 96 ppi - anything from 300-600 gives excellent results with a laser. And 300 ppi is more than adequate, so that’s usually what I use. Higher PPI is only really useful for very tiny engraves, like engraving on a grain of rice.
LPI (Lines per inch) is how many times the laser will travel back and forth over a particular area as it moves up while engraving. It has absolutely nothing to do with either PPI or DPI. If you specify a high LPI, the beam will travel over areas that have already been lasered, deepening the engrave, charring the wood more, and making it darker. High LPI also looks better when etching anodized aluminum.
Hope that explains it. Use 300 PPI for your raster work and set the LPI based on how deep/dark you want to go with the engrave.
This is kind of a black box in the Glowforge software.
First, what’s going on, your PNG is defined as X*Y pixels (say, 500x500 pixels). The browser has its own interpretation of Pixels per Inch (96). So, when you upload a 500x500px image, it’s taking that and interpreting 500/96 as the size of the image. When you get into high-resolution images - say you exported a 5x5” image at 300 PPI, your image is now 1500x1500, but when you upload it to the app, it will size itself to 15.625” instead of 5x5” @ 300 PPI.
The black box side of it is what happens to the image when you scale it back to 5x5”? Is it increasing the PPI as you scale the image down? Is it keeping it at 96 PPI?
What one can do though, is embed your hi-res raster images into a SVG file. It will maintain the correct size when you upload the SVG. I’ve also seen a noticeable difference in testing these prints when embedding 72, 300, 600 PPI images into the SVG.
Thank you for those answers @jules, @eflyguy, and @jbmanning5. That is some really great information!
Since it sounds like there is no more troubleshooting to be done on this thread, I’m going to move it to the Everything Else section. If you are still running into trouble, please open a new thread in Problems and Support or reach out at support@glowforge.com.
That’s an excellent way of describing what I’m seeing, although to be more exact, my intended 4x4" @ 300 PPI .png uploads to the app and sizes itself to ~ 9.9" (~121 PPI).
I have tried what has been suggested, that is, embedding my hi-res raster images into the SVG file, but while that maintains my desired image size of 4x4", the image can clearly be seen to be downscaled to 360x360 pixels (4x4" @ 90 PPI). A side by side comparison of the unchanged .SVG vs. the scaled in the GFUI .PNG can be seen below. To my eye, the .SVG on the left looks grainier and more pixelated while the scaled in the GFUI .PNG looks somewhat smoother. This gets back to the black box side of what is the PPI of the image on the right… I guess the next thing to try is scaling an even larger image down in the GFUI and seeing how that compares.
What you see in the UI in no way represents what gets sent to the machine. The UI adjusts what’s shown based on settings, but that doesn’t reflect the quality of the file sent for processing.
So when you right click on the input files (presumably .SVG) for all of those test engraves, they’re the same width and height in pixels? The only difference was the resolution of the raster image before you converted it to .SVG?
Sorry if I’m belaboring this. Again, new to both vector imaging and laser engraving. It is incredibly helpful to see side by side comparisons of test output!
Correct. Each was a vector copy that was rasterized at a particular PPI, embedded into an SVG, and then uploaded into the app, and all imported at the exact same size.
