Thanks very much to you all. And @jbmanning5, those examples are what I was looking for and I think you really helped with that.
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Great community responses! I’m sure you found it the Glowforge online manual for that function that was published when it was released, or example videos that show you how it works. Can you point me to where you found it?
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You are joking aren’t you?
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I think this is a fantastic question, because I learned something from it. My friends in UX probably know this, but it never occurred to me to be careful about using the word “options”. These sections should be labeled “___ Settings”. Maybe options is appropriate for a panel of checkboxes, but here it’s just one more tiny thing to trip people up.
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That is very interesting and not the way I thought it worked. (Not saying you’re wrong. Just saying I didn’t know that until now.) That’s going to take time for me to think about it in those terms. So, I’m curious… When you took out white, did you just adjust levels globally? Or substitute white with something darker? Or…?
Also, (to all, not specifically jbmanning5) people keep using “%” when referring to power. It’s not and I don’t want people to be confused. There is no unit of measure. It goes from 0 to Full and is not linear. In other words, I don’t want people thinking that 50 is half of 100 or 52 is half of Full or something. That’s not how it works.
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That’s definitely the way it works. See other discussion here where it tripped me up. I would personally prefer it not do this for formats with transparency, or at least have a checkbox somewhere to toggle it.
I think in this case he was talking about “% gray” in the image, not % power in the GFUI. But in a similar way, that’s not entirely accurate, if we’re being picky (and what’s more fun than being picky?) “1%” is too coarse of a measure. There are lighter shades than 1%: even at 8 bits per pixel, there are 256 levels, so a single percent is going to cover 2-3 steps. In any event, what the Glowforge ignores is pure white (in my example, 255). If you’re using the min power setting and don’t want there to be “bald spots” between white (laser off) and almost-white (laser on at min power), you should remap your image to avoid any pure white. @takitus shows an easy way to do that in Vary power glitch (+ workaround) - #14 by takitus.
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Again, definitely not doubting that’s how it works… Just that that’s not how I thought it worked up until this moment. 
TOTALLY agree there should be a checkbox. I’d say that checkbox should allow transparency AND white to be ignored in the setting so that both are untouched by choice. To me, that’s what “0” always meant. I’m not really sure what workflow would make the way they have it be preferred by somebody.
Hmmm… Not the impression I was getting… “minimum power 5% and max power 80% means: 5% power”
And I’m not saying it’s him. It’s many people on the forum. And it will confuse people into thinking that 49 is 1% less power than 50, when it’s not. I wanna kinda nip this before it really becomes a thing is all. It’s more like “Set weapons to maximum.”
There are image formats that don’t support transparency, or people who don’t really think about transparency and expect the Glowforge to do what they mean. For example, a JPEG with a white background and a photo cropped to a circle.
There’s some ambiguity there around what the user wants, and they would be surprised to find the laser firing outside of the circle. It’s not completely insane to reserve one color value to stand in for transparency, but it would be nice if it were documented and if it were possible to turn it off if you’re using a PNG or SVG that has actual transparency.
We’re looking at two different, but adjacent sentences: “Your min setting will be minimum power for 1% and the max power you set will be for 100% gray (which is actually black).”
I didn’t mean to imply you didn’t have a valid point. I agree, we should all be in the habit of referring to Glowforge power levels without instinctively adding a “percent”, because they’re not percent. Kind of like how it took me a while to unlearn “degrees Kelvin”.
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If I’m using a masked material like PG, I always set it at 5 power level for min. Otherwise set at 0 it will burn the top of the masking away but not the glue and it’s a PITA to clean it off (okay not hard, just a brush of alcohol, but another step).
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Ah! So you’re saying in the area where it’s white, the head would still move across it and fire the laser at power 0. Where you and I would have made that part transparent, somebody else may not intuit that and not get what’s happening. Sure, that makes sense.
So! I think what I’d really like to see is 0 representing white. To me that just makes sense since white is included in greyscale. With an “Ignore white” checkbox so the head doesn’t travel unnecessarily.
Man! This power 0 thing is a real surprise to me! So let me see if I get this… If you set min power to 5, anything that’s gray will at least do 5 power, but white is still “real” 0?
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@Chris1, @Tom_A and @jamesdhatch: Keep teasing it out. This conversation is uncovering important variables that I didn’t realize.
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Yes. 5 will burn the glue but not the material underneath (on my PRU - you probably want to check your prod unit for your number - I expect it’s pretty close).
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No, you’re right. I referred to power as percentage and it’s not.
I used the output method @takitus mentioned in the other thread - it’s the easiest way I know of to quickly and accurately change pure white.
I could have changed it to 254 for absolute precision but I just dragged it a bit and ended up around 249-250. It was close enough for my needs.
Which leads me to, @chris1 - yes, there is more granularity in there than 1-100% gray. For the action of burning wood though, I find the scale of 1-100% accurate enough for my purposes and it’s an easier idea to relate than .028% gray and in the end, we humans can’t really discern between grays very well. I think we can only “see”/identify about 30-35 shades.
I can see where this trips people up and I can see both sides of how it should be done as far as minimum power should be minimum power for the project, or whites should be ignored. Or transparency should be ignored. I feel like they implemented it correctly but the process of not allowing pure white in a file isn’t exactly common knowledge.
I can see cases where i would want pure white just ignored - and I can see cases where I would want it marked (like my above example). Maybe a checkbox here might be best, maybe not. The merits of such would need more than the 3 minutes I’ve thought about it.
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Since we are nitpicking about accuracy of statements - no. As part of the Glowforge motion planning, it’s intelligent enough to use pure white as a motion boundary rather than traversing across the raster file edge to edge.
For example, if I had a 500px x 500px raster image with a white background and in the center, I dropped a black circle to engrave, the motion planner wouldn’t make it traverse the full 500 pixels across X every line - it would travel (and overshoot just a bit, I believe) just for enough to start the next line of engraving. That’s a simplified example - but the answer is, it will just travel just as far as it needs to make the next engrave line.
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And on a further note - having 0 populated in the min power box is actually a bug more than likely. It should really be populated with a 1. I’m not at the app at the moment - but I’m relatively certain that If you change the input, you can’t go back to 0. The minimum is 1.
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The preview is accurate enough to show this in the UI. You can just download the image I posted above, set it to manual engrave, vary power, and if you set “min power” to something like 50%, you’ll see there are “holes” in the result wherever the file is pure white. Regardless of what you set the minimum to, it will skip over white areas. So if you want to do something like 5% minimum to ensure you burn through the masking, it’s imperative to make sure there’s no white-white in your image.
I realize this is now probably belaboring the point, but it might help people in the future who stumble across this topic in a search.
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This thread is an example of how incredibly valuable the entire GlowForge Experience is. I feel like I am in a master class. Thank you all for taking the time to share your valuable experience.
Now I just need another cup of coffee and to reread about half a dozen times to wrap my brain around it all 
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Another thing learned today. Thanks!
I hope he is…because I fear we’ll never find that.
To paraphrase something Dan said to me one time…to the laser, white is like looking for a sheep in a snowbank.
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