View Full Version : Photograv consistency

Doug Fennell
01-15-2008, 12:55 AM
What's the trick?

Photograv ver 3 gives oddball power settings on all of the materials I've tried, but granite is the one I'm most concerned with. At 300 DPI, it ALWAYS hovers at or about 87 power and 100 speed. These settings will obliterate any image sent to Granite on a 45W Helix. The magic number for me when all is right with the world is 33 power and 100 speed.

Here's the question... what method do you use in processing your pictures in photo paint/ photoshop / (insert favorite image processor here) to achieve consistant results using the numbers that work with your engraver? In other words, what do you do to your photos to make them all work at say, 33p and 100s? Is there a way to sample the overall brightness of an image that works and tune subsequent images to aprox the same level? Or another method that works? There must be a way to quantify a process.

Frank Corker
01-15-2008, 7:25 AM
Hi Doug,

I agree with you around the power setting being 33. I still can't understand why the power settings are so high. I have set Photograv 3 to the same settings as 2.1 so you would expect to see a similar speed/power ratio, but it doesn't. The actual images appear to be very similar in appearance but the only way to know for certain is to run tests on granite.

Rodne Gold
01-15-2008, 8:04 AM
I have never found mnfgrs setting to correspond with real life setting or even be close.
Use Photogravto do the 1 bit conversion and then use your normal settings that work with the material.
I use one setting in photograv , the light cherry for EVERYTHING!!!!
Works well on all materials for me.

Frank Corker
01-15-2008, 8:13 AM
Interesting. I'll give that a try, is that with 3.0 or 2.1? I have always used cherry wood when I am engraving glass, but use the recommended power settings regardless.

Rodne Gold
01-15-2008, 9:30 AM
Ver 2.1
I think the program is somewhat expensive for what it does and 2.1 is definately not accurate in terms of doing it all including giving you the correct settings. At the end of it all, it merely converts greyscale to dots of black , thus whatever you would normally engrave black at is the setting one would use.
What you have to be aware of is the heat affected zones of the material. Essentailly this will determine the resolution you should or can use.
With a normal lens , the absolute best resolution any material can hold is 300 dots per inch. The size of the spot is 1/300th of an inch.
Stuff like wood which "burns" the edges of the spot beyond the spot size must be lesser resolution otherwise it gets messy. Granite and marble etc can hold finer lines.
It's better to err on the side of coarseness than detail. Most pictures most of us get to reproduce are bad anyway or not really 100% suitable, so it's already a compromise.
I find P/grav more usefull for doing multicoloured vector based clipart and logos than for pictures.

Doug Bergstrom
01-15-2008, 2:41 PM
I am glad I am not the only one see this issue. We were doing a large plaque job with photos that we do every year and matching always becomes an issue. On Marble or hard surface material I tend to use the settings that come out of Photograv and they work well. (vers. 2.1 have not made the commitment yet to the new version) For wood we use the cherry setting and do an interactive conversion. We then lighten the image using the levels adjustment until it looks like it would "print" a little too light. Then we save that file but when we output to the laser we use a standard wood setting that we have developed for our laser through trial and error. This setting uses a lower power and slower speed then what comes out of photograv. The end result is a deeper and darker engraving with more open areas that better resembles the original photo. Overall I do not find this method user friendly and only a couple of us in the shop can really do it with some consistency. I have about 15 years experience in Photoshop and have taught courses on color theory, photo and print and I still get results that seem to vary every time we engrave a photo. I am searching for a software that will make this more user friendly and easier for anyone to use. Has anyone tried the new software that just came out for engraving photos? I cannot remember the name, it was just in one of this months trade journals. I believe it might be from Gravograph. I will see if I can find it the name and repost.


Doug Fennell
01-15-2008, 6:56 PM
What we really need is a way to judge overall brightness and threshold of an image. Not like a histogram that looks at the entire image and plots a graph, but a function that gives a number value. For example, lets say the "perfect image" has a brightness value of 6 - then adjust your current image to have an overall brightness value at or approaching 6 - then you'll get a good burn without overburn using your standard power/speed setting.

As another example, when your burn MP3's to disk, you normalize their output - that way they all play back at the same volume level. Is there a way to process images at the same volume where volume=brightness?

Larry Bratton
01-15-2008, 9:41 PM
How can you expect to get totally consistent results with natural materials such as marble and granite? They are totally different materials with different physical properties. I engrave granite at 45pwr 100spd and get fairly consistent results.

I have no idea if this matters at all, but it seems to, I warm the granite up so that's not cold to the touch before running it. I never use that Photograv information. I use my Epilog recommended settings as a starting point and experiment from there.

I listen to what Frank says because he's usually right on with his advice.

Just my two cents worth.

Doug Fennell
01-15-2008, 10:12 PM
Larry, there's no way to negate the inconsistancy of a natural material - it would be impossible to do.

The intent of the post is to find a way to null out the software variables so all of the images are level brightness wise. Whatever happens when the laser hits the stone is fate. The point is, why trust the software variables to fate? They can be controled.

Bill Cunningham
01-15-2008, 10:39 PM
I generally use the black granite parameter to process the photo, but I virtually never use the power/speed setting that photograv recommends.. The black granite setting may very well be the same as the cherry wood parameter, I have just never looked at the actual internal settings that closely.. As for pre-processing, I generally use the brightness/contrast/intensity setting and adjust it 'till it looks right' can't explain it better than that, but it seems to work for me.. The picture below, is just plain H.D. Absolute black granite with a thin film of titanium white oil paint to bring out the etch

Doug Fennell
01-15-2008, 11:16 PM
Bill, when you paint it, do you let the paint dry a bit, or wipe it off immediately?

Doug Bergstrom
01-17-2008, 9:27 AM
With many of the harder materials like granite and marble we tend to get a more consistent result. Wood has had many issues with consistency. In looking at an Alder plaque we produced about two years ago and the new plaques that came in this week from the same distributor there is definitely a difference in the quality of the plaque. The old plaque had a better match in wood and grain. The joint was almost undetectable. Some of the new plaques look like two different types of wood and when etched the engraving looks completely different from section to the next. Maybe the recent surge in wood use for lasers has brought up the demand and in turn is lowering the quality.

Bill Cunningham
01-17-2008, 9:18 PM
Bill, when you paint it, do you let the paint dry a bit, or wipe it off immediately?

Doug, I usually take a very small amount, (about 1/4" dia. or less, blob ) and using a fine edged body filler squeegee I spread it across the entire etched area of a 12 x 12 tile. Also, I take black shoe polish (the liquid type is fine) and blacken the edges. I then let it sit at least over night. Oil paint drys very slowly, and it's still wipeable the next day.. At that point I take a soft cloth, and rub all the oil paint I can off the surface. Whatever the granite will absorb has been absorbed by that time.. Ideally, it should sit for several more days, before using a polymer stone sealer to waterproof the entire thing front and back.. Just follow the directions on the container. The polymer is available from home depot, and is the same stuff you would use to seal a tiled shower stall..