Need IMMEDIATE Help!!

[Jerrod Treangen]

I just received a call from a client with regards to a granite piece I did for him. He has complaints that the picture is grainy. The file he sent was fine, but it did turn out a bit grainy. Not sure if it is an error in converting or what. Laser Pro 30 watt here, utilized photo engrave, 100 speed, 50 power. Any advice greatly appreciated so I can rectify this! Ideas on DPI settings? Laser sketch granite used. HELP!

[Bruce Volden]

Jerrod,

I don't know which program you use to dump to the laser (I use Corel 11) but if things looked good on your monitor it should look good on the granite / glass etc. (Grainy woods notwithstanding!)
When I engrave granite I'm running 25 speed / 30 power 300 DPI 25Watt machine.
I have found by slowing the speed the resolution seems crisper. If you were to draw a thin vertical line and engrave it @ different speeds, then look at the engraved line with a loupe or strong magnifyiny lense you most likely could see a difference with how the "dots" line up. I'm thinking it has something to do with the laser ramping.
Perhaps this is just my machine and you have a fussy client?? Bruce

[Jerrod Treangen]

Coral 12 here. Not sure what is going on......any ideas on DPI from people that work a lot with granite?

[mike wallis]

Are you sure the grain is in the picture and not in the Granite? I recently did some testing with Granite to find the most contrast without breaking into the speckling of the Granite. I found on my Epilog mini 35watt a speed of 66 and a power of 23 @ 300 DPI was optimal. Any more power than that and I started to break through into the speckling. Oh yeah... I always process with PhotoGrav and never use LaserSketch.

Good luck
Mike

[Jerrod Treangen]

Well I am stuck with laser sketch for this job. I did use photo grave. It appears it may be that the speckling is creating the graining? Not sure if the rest is to deep or what? 100s 50p on a 30w. Not sure if it is a DPI issue or what?

[mike wallis]

Hi Jerrod,
What DPI are you printing at? I find that anything over 300 DPI on Granite tends to over burn the surface and reveals the speckling. LaserSketch Granite should work, the reason I don't use there Granite is most flooring places carry Absolute Black that I find is a better quality and cheaper (no shipping charges).

[Jerrod Treangen]

Mike,

What speed power setting do you use? And of course...what type of machine you have? How about processing picture? How do you go about that? I open in coral paint, resample, send to photograv, inport, then print. Same thing you do? Big thing is what dpi, power, and speed?

[mike wallis]

Jerrod,
I use Photoshop for adjustments/resampling then send to Photograv. I always print 300 dpi For Granite with a power of 23 and a speed of 66 on a Epilog Mini 35 watt. My setting swill probibly vary because of different machine types but this should be a good starting point.

[Barbara Sample]

I just received a call from a client with regards to a granite piece I did for him. He has complaints that the picture is grainy. The file he sent was fine, but it did turn out a bit grainy. Not sure if it is an error in converting or what. Laser Pro 30 watt here, utilized photo engrave, 100 speed, 50 power. Any advice greatly appreciated so I can rectify this! Ideas on DPI settings? Laser sketch granite used. HELP!

Hi Jerrod,
I have a 35 W LaserPro also and I use SuperBlack Granite from LaserSketch, I use a setting of 12 power and 30 Speed. I know that doesn't sound like much power and speed, but granite only needs to knock off the top layer to look good. I use that setting all the time, with good results. I have a photo of the granite memorial that I did for my nephew on my website, take a look at it, that is the setting that I used for it.
www.rgilengravers.homestead.com
I think the setting that you used was too much for the granite. Have the guy bring it back and use the edges to see what you get. and then try it again,
If I can be any furthur help let me know.
PS, I also use photograv to process it, and always use 300 dpi, I have found that any higher than that, washes the photo out too much.
Also, size it in Corel before you use photograv, or you will get black spec's on the peice.

Good Luck,
Barbara
RGile Engravers

[Rick Maitland]

Barbara your tiles are awesome!! I like the painted ones the best. Do you use all the same settings when you engrave the tiles that you add color to?

[Rodne Gold]

You have to understand how the laser works with photos to really get all this right. Essentially the laser can engrave 2 colours , a dot or not.
The dot size a laser can engrave is governed by the spot size which is generallly 0.003" at BEST. Thus essentailly the laser can really only ENGRAVE 300 spots per inch. This is all good and well , but the material might not even be able to HOLD a resolution of 300 dots per inch as there is a zone outside of the dot that is also affected by the laser beam , dependant on the material. Ok you might say , this means that my graphic can have 300 dots per inch of printable info - but this is NOT so. (As an aside , one refers to pixels per inch and not really Dots per inch -PPI )
The graphic has shades of grey , and as we all know , the laser can print ONE colour. So what it does is to represent a shade of grey by filling in the cells of a matrix of dots. Lets take for example a 3 cell by 3 cell matrix with another next to it.
Fill in ALL the cells and the 2 matrices appear black , fill in only the centre cell of each and they appear light grey. This is called half toning and its how the laser represents shade of grey.
So now the question to ask is how many CELLS can be printed per inch of output and that is at maximum , about 100 and is probably less.
So how does this affect you with photos. Well in the first place , each cell represents a pixel , thus image size when converting to engraving is important , ideally , 100 pixels per inch of output is ALL that is needed , so when scanning or sampling a picture , SIZE counts. If you want a 4" x 4" picture , the picture has to be 400 pixels x 400 pixels (dots per inch when scanning are equivalent to Pixels - only time that is so and the actual expression DPI in scanning is actually wrong , it should be PPI)
So when scanning , you have to know output size , and the formula for either conversion or scanning is DPI/PPI= output/input X 100. So if you have a 6" pic and want to print at 12" its 12/6x100= 200ppi. Scanning at higher resolutions does nothing but confuse whatever package you use to print etc and makes for a bigger file as well as lengthening conversion time.
OK now you got the Photo size right , what do you do to your laser to get it to print right. Photograve essentially does a translation based on the materials and laser parameters to a one bit image - IE Photograv makes the shades of grey and "cells" into black bits and it sends thos black bits to the laser , thus bypassing any laser conversion of greyscale to cells. It does a whole lot of other stuff too like sharpening , edge detection etc. All of this you can do yourself in software and the laser driver , but you got to know a lot of things to do so. If you are using photograv , it doesnt really matter whether you do engrave at higher than 300 dpi capability as the program takes into account spot size and how material reacts and will thus compensate for dot overlap and so forth. All you do is take more time to do the said engraving at high dpi , however higher dpi WILL compensate for laser inadequacies like motion system slop , and a whole lot more , so in effect engraving at high dpi will often reduce banding and misregistration problems evident at lower DPI.
Ideally , if not using photograv 300 dpi is adequate and often one gets FAR better resolution at MUCH lower than that If the laser system is up to snuff.
We do 2 types of marble and granite engraving , 1) Direct where I use photograv at no more then 300 dpi resolution and 2) Blasted thru a mask.
Now with a mask the spot size of 0.003" will NEVER allow the blast particles to get thru the mask properly and we also need some meat between holes so the blast media doesnt erode the resist. So we use gross Pixels per inch , sometimes as low as 25 and very low dpi so that we get big enough holes in the mask to actually allow a blast. Even at these gross PPI's the pic quality is not bad at all , but looks more like granier newspaper pic.(but is obviously a LOT deeper than laser engraving)
There are limitations to working in stone with a laser , in general the customer cannot expect a continuous tone type output unless everything comes together perfectly and that is rare. Graininess would be caused by either a poor resolution photo or non ideal specs used in Photograv or your conversion , most probably wrong spot size or the like. Of course it also depends on the material , for example what does the beam DO to the material. Lasers work 2 ways , vaporization or thermal shock. Vaporization removes material by exciting them to such high temps thy vaporise , generally the will give a "clean" dot , thermal shock will induce the material to fracture at the area the beam hits (glass engraving) and gives rise to a rather uncontrolled dot or hit. In a stone like granite , you can either hit the stone with lower powers , resulting in a combo of thermal shock and leeching colour , or hit it with a ZAP of power which results in a fracture mostly (and possibly a burn)
Stones are natural stuff and will react differently dependant on its composition, so ideally one has to experiment with the stone and laser power. Best way to do this is a series of filled squares which will firstly give you an indication of power levels , engrave these at various power settings and see which is the "whitest"
Then take those settings and engrave them at various resolutions and check again for whiteness or appearance. Use those power settings and resolutions to engrave. Ideally you want the lowest res that still looks good.

[Alan Young]

Wow Rodney I am always amazed of the detail you provide. I hope you don't have to retype all that all the time. I second what Rodney says and have also found like some of the others that low power is the key to a good image on Granite. I use black granit Floor tiles from Lowes and have had good results if the power is low, to much power and all I get is a gray blob.


Alan

[Kevin Huffman]

Hey Jerrod,
One thing you might want to try is on your Raster Tab, change your Dithering to Error Diffusion. I have had a couple of customers complain of grainyness and after changing that it fixed the issue.

[Barbara Sample]

Barbara your tiles are awesome!! I like the painted ones the best. Do you use all the same settings when you engrave the tiles that you add color to?

Hi Rick,
I do not use any special setting when I paint them. I do however use two different marbles. I buy some of the tile from a marble stone distributer in 12 x 12 tiles, and cut them and then finish them by hand. My husband cuts them for me, and I sand down the edges. When I am lazy, I use a magic marker on the edges. It really does not look bad.
On that marble I get the best results. I have tried Laserbits and lasersketch and it just does not give me the good result that I am looking for.
I also have to use different setting for their marble.
So, even though it's more work, that's what I do.

As far as the colored ones, I just used oil paint, used the original to show me the colors and started to paint in the lines, I then rub off the excess. It takes a little time, but very nice results. Although my paintings come out looking like a watercolor, so I asked a friend of mine to paint a peice of granite that I engraved with fruit and she hasn't finished it yet, but I hope to get it looking like a real painting, that way I can offer both styles in my store.

Thanks for the compliments, it makes me feel good.
Barbara