Cross Hatch?

[Chuck Stone]

I've noticed that when I do 3D files and have a deep background, the
black areas come out with a cross hatch pattern. It could be that I
have something set incorrectly, but I'm not sure what.

My camera isn't working right (when it works at all! ) so I couldn't get a
good macro shot.. had to crop this out of another photo. It only shows
the lines in one direction but it runs both ways. Looks like I've lasered a
pattern of burlap into the background.

I've used the defaults (500 dpi, PPI is on Auto) It's a GCC Mercury, 30W
and I'm lasering this on Corian, but it does this in other materials, too..
just doesn't show so much on wood, since the grain obscured it. I can
change the dpi and PPI, but don't understand quite enough about the
relationship between the two to make an intelligent change.
Anyone else have this happen or know where I should look?
Thanks for any input..

[Dan Hintz]

If it's 100% black, you're most likely seeing moiré patterns created by the motor steps and the laser pulsing... only way to get rid of it in that case is to use a higher resolution.

[Chuck Stone]

Thanks, Dan .. I wondered if it had to do with the motors, since it is so
regular. I've upped the resolution and it did get slightly better (I should have
mentioned that) but didn't go away. Plus it upped the laser time significantly.
So far the best I've been able to do is an extra pass slilghtly out of focus
and that sorta/kinda helps to smooth it out a little.. but it doesn't eliminate
it completely.

Oddly, it only shows up in raster as far as I can tell. Not that I've vectored
parallel lines close enough together to really tell..

[Scott Challoner]

Rather than using a solid fill color, you can aso use a pattern or postscript fill such as stucco to give a little different texture so you don't see lines. You can alter the shades within the postscript fills too.

[Chuck Stone]

I actually want a plain background, but this is what I got. The background
I started with was a star field, but it didn't really look much like a star filled
sky with a woven background.. :p

[Dee Gallo]

Chuck,

What if you engrave as usual, saving the file of course. Then, select the background shape and put a different pattern in it which is overall pretty dense. Without moving the piece, engrave that over the first and see if it gets rid of the weave... or at least makes it more acceptable?

:) dee

[Scott Shepherd]

Making the background color 95%,90%, 85% or 80% gray instead of pure black can also solve this problem. Obviously the smaller the number, the more halftoning it will do. 90% is a good place to start.

[Chuck Stone]

Hi Dee ..

I have done that, both with the same focus and with a slight shift. The
background right now is solid black, but it did the same thing with black and
white dots. The dots got lost.

I have some better pics of the pattern. This is what the final product will
look like. I lasered the Corian, made a silicone negative, poured resin with
bronze in it and buffed it with steel wool. Still shows the pattern pretty
hard.

[Chuck Stone]

Making the background color 95%,90%, 85% or 80% gray instead of pure black can also solve this problem. Obviously the smaller the number, the more halftoning it will do. 90% is a good place to start.

Thanks, Scott.. I'll try that next.

But for my own education .. why is that? It even does it in the white areas,
although much less. (see the raised areas, those might have been in the
10% range, not 100%)

I made it worse by needing to laser two or three times just to eat away
enough material to give me the depth I needed.. but the lines stayed in
the same places, so I think it is something the software is doing that I
can't see..

[Dan Hintz]

Lasering multiple times can actually be useful... change the pattern (black density) with each laser pass, and if you get the sequence and choice of patterns correct, it'll smooth it out. It will take some trial and error to figure out what patterns are best since we have no way of knowing exactly what patterns the driver uses with each density.

[Chuck Stone]

Do you think varying the dpi or ppi would help?
I think changing the dpi will affect the image size, though

I dunno.. math gives me a headache..

[Scott A Engle]

Hi Chuck,

This is off-topic for this thread, so feel free to respond via PM if you want. I was wondering if you had to get any special permissions to use those Star Trek images.

The reason I ask is that I was considering creating a product using the quote "Live Long and Prosper", but I didn't want to tick off CBS (which owns all the rights to Star Trek).

Thanks in advance,

Scott

[Dan Hintz]

If it involves the word "product" and uses something famous, you're in for a tough road. And it's not CBS you have to worry about... any copyrights for Star Trek (and spinoffs) belong to the Roddenberry estate (which I believe is now in the hands of Gene and Majel's son). I don't believe "Live long and prosper" is copyrighted, but they can still sue you if they feel like it, and if it's associated in any way, no matter how loose, with something else on the show, you're toast.

[Mike Null]

Chuck

I would try a couple of different things. One change the dpi settings with each pass. Two, try de-focusing the machine by about 1/16" to see if you can get a softer image. Three, check your mode settings in your driver. See if you have a relief mode and try that.

If you have the option to manually adjust the half-toning algorithms experiment with that a bit.

As a last resort convert the image to a bitmap and engrave it. There you can use any of several conversion methods to prepare your artwork.

One more thing--you can insert a subtle fill as background using the post script fill tool. We used to do that when making patterns for spin casting. This will take some practice but it will work.

[Chuck Stone]

Hi Chuck,
I was wondering if you had to get any special permissions to use those Star Trek images.

I didn't get permission.
If they want to sue me for making a gift for one of their writers
and one of their cast members, so be it. :eek:

These wouldn't be offered for sale.. ever. They're a one time casting.
(and judging by the amount of work entailed, I won't be producing
anything like it ever again..)

[Chuck Stone]

Chuck

I would try a couple of different things. One change the dpi settings with each pass. Two, try de-focusing the machine by about 1/16" to see if you can get a softer image. Three, check your mode settings in your driver. See if you have a relief mode and try that.

If you have the option to manually adjust the half-toning algorithms experiment with that a bit.

As a last resort convert the image to a bitmap and engrave it. There you can use any of several conversion methods to prepare your artwork.

One more thing--you can insert a subtle fill as background using the post script fill tool. We used to do that when making patterns for spin casting. This will take some practice but it will work.

Well .. I varied the dpi from 500 to 1000, changed the PPI from Auto to 1000,
changed the focus 1/16" and then 1/8", changed the halftone from Error
Diffusion to Dithering (2x2 matrix, dot pattern) but so far the best I could
do is scrape off the lines with a tiny chisel. :eek:

I'm not sure about the post script fill tool, but I could easily insert a
background. This is 100% raster image done in Photoshop and I'm sure
I could find that option somewhere.. I'll look.

Perhaps I could render clouds of 99% black on a 100% black background?

[Chuck Stone]

Just an update..

Changing the DPI, PPI (wouldn't affect raster anyway) and doing a polish
pass don't seem to make a difference. Still looks like I'm running the laser
through a screen. Changing the dithering options changed the output, but
not affecting the cross hatch in any meaningful way.
I'm doing several passes, and the lines are always in the same position,
both horizontal and vertical

.. just wish I knew what was going on 'under the hood'

[Scott Shepherd]

Did you try making the background 80% gray yet?

Also, it could be a bearing issue. I just had a job and banding was off the chart. I changed my bearings and all was good again. Don't overlook it being a mechanical issue.

[Mike Null]

Changing the dpi setting in your machine will definitely change the raster result.

I agree with Steve--it could well be bearings.

When your machine is off can you move the carriage around freely? If so you may be able to feel bearing wear.

[Niklas Bjornestal]

Do you use any "scaling" (in the advanced settings tab when printing). I had some trouble with banding when engraving anodized aluminium and mirrors that went away when i changed the scaling to 0.

[Chuck Stone]

I'm not going to overlook anything, believe me! I appreciate the input so
I can try out things I haven't thought of.

The scaling is off, and I did an 80% with no change. (now that I think
of it, might have been 90%) Also filled in one area with a pattern but that
didn't make a difference.

I can move the head and rail freely, but that doesn't mean the bearings
aren't a problem .. I just have nothing to compare it to. I suppose I should
just take them out and clean/inspect just because. I know the previous
owner wasn't up on the mechanical stuff, and I haven't used it enough to
really dig into it myself beyond routine maintenance. I know the bearings
and bushings wear over time, and some materials throw off particles that
can become lodged in tight places .. especially with those places have
some sort of lubricant in them.

But the pattern is so regular.. and repeatable.

I think the next time I run it, I'll offset the position with a few sheets of
paper just to even it out a little.

Fortunately, these are masters for a silicone mold. So I can fill in the
background with vaseline and mineral spirits before I pour. It won't get
rid of it completely, but should help to minimize it when I pour the positive.

Thanks for the ideas, people .. still working on it!

[Roy Brewer]

...where I should look?
Chuck,

Sorry if I missed this question in this long thread, but you do have color management turned OFF(or Simulate OFF in X5), right?

[Doug Griffith]

I'm not sure about the post script fill tool, but I could easily insert a
background. This is 100% raster image done in Photoshop and I'm sure
I could find that option somewhere.. I'll look.

In PS I would try:

filter:noise:add noise:gausian
or
filter pixelate:mezzotint:fine
or
filter:sketch:halftone pattern:note paper then levels

[Andrea Weissenseel]

Chuck, in the manual (pg 62) are samples for selecting the dithering. There are sample pictures included - I would try using "Bayer" with a 2x2 raster and "Enhanced Dithering" checked. There is also a Tipp of making a polishing run when engraving 3D, with a complete black mask 100% Pwr 100% Speed

[Rodne Gold]

That cros hatch thing seems to be an issue with 3d engraving on the GCC machines , we have had that and I have tried all sorts of strategies to remove it with no luck whatsoever. I do a lot of masters for casting and never use 3d for em , the results are too unpredicatable. If I want a 3d effect , I might assign 3-5 colours to various elements and engrave with 3-5 different depths , this actually works better than true 3d
The best results you will get using 3d are with substrates like MDF where the croshatch type moire pattern tends to dissapear , the harder the substrate like acrylic or corian , the worse it becomes.
IMHO 3d engraving is a waste of time. If I want to do true 3d masters , I use artcam and a cnc rotary machine (my Tekcel and sometimes my Roland) and the results are far superior to the lasers output and are much more controllable.
Check that you have the latest firmware and drivers for your machine , they might have improved 3d in them,,not sure tho,

[Mike Null]

We did our masters in acrylic using CorelDraw with a patterned background and various shades of gray. These were run on an old Epilog.

Never tried to do 3d art for masters.

[Chuck Stone]

Thanks for more ideas.. I'll be trying these this morning/afternoon.
(these things take about 4 hours!)

Roy.. no color management issue, running straight out of Photoshop because
1. I know it better, and
2. I'm not sure how to work with layers in Corel yet. I haven't spent
much time in Corel since version 3!

Doug.. I haven't done those particular things, but have added some
texture, which didn't change anything. Adding noise seems counter-intuitive,
but it's worth a shot. Are we hoping to keep the software busy with the
background so it doesn't add it's own?

Andrea.. the polishing run didn't change much, it seems to put down a
lighter version on top of the heavier one, cross hatch included. I didn't
try the Bayer yet, but used the enhanced dithering and a couple of the
other options and 2x2 (can't remember which ones right now)

Rodney .. I'm not actually using the 3D settings, although I have. (same
results) I'm running it in Black and White mode, and I've assigned 16 levels
of power/speed combinations. I'm getting an OK 3D effect with a heavily
modified grayscale image run in RGB mode (haven't tried others only because
most of the tools I use in Photoshop are only available in RGB mode)
I do have the latest drivers/firmware, but no .. they don't seem to have
done anything in the 3D portion of the software that I can tell.
Since my work is strictly hobby, ArtCam or a CNC machine would be hard
to justify .. as would the cost of having someone else do it for me.
Besides, I'm a stubborn old Yankee :p I'll learn to make it work, or I'll
learn to love it the way it is.

I'm coming to think that no matter what is in the file, this is just something
the driver is doing in the background .. on it's own. It seems to be too
regular and repeatable to be random. I'll be digging into the bearings this
morning and see what I find, and have a few suggestions here that I can
incorporate, too.

While it isn't true 3D, I've done some nice things with it in the limited way
I've been using it..

[Mike Null]

Chuck

If you are running in the b/w mode do you have the option to set it for Jarvis or Stucki within your software?

[Chuck Stone]

Chuck

If you are running in the b/w mode do you have the option to set it for Jarvis or Stucki within your software?

I do .. so far I think I've only used the Floyd Steinberg though..

I just don't see what there would be to dither in solid colors, though.

[Niklas Bjornestal]

Rodney .. I'm not actually using the 3D settings, although I have. (same
results) I'm running it in Black and White mode, and I've assigned 16 levels
of power/speed combinations.
You shouldnt use Black and White mode, you should use Manual Color Fill. If you use Black and White mode it convert the colors to greyscale and dithers them.

[Chuck Stone]

You shouldnt use Black and White mode, you should use Manual Color Fill. If you use Black and White mode it convert the colors to greyscale and dithers them.

OK, thanks... I never knew what that was, but I don't recall trying that one.
I think I selected it once and the little leaf image looked like crapola, so I
probably just thought it was for .. um .. I dunno .. people who do crapola
engraving? :p

I'll give that a shot in the morning.

I still didn't think it would dither since it is a solid black area. But I chose
different options just to see if it would change anything. Never tried this
one though..

I think someone else suggested it too .. but when I heard color fill, I was thinking
it was something in Corel.. didn't realize it was in the driver

[Chuck Stone]

Update:

Manual Fill : No change in the cross hatch. I sanded out the lines with 150,
220 and then 320 grit. Did another pass, sanded again. Forgot to change
out of Manual Fill and the grayscale lased as if it was full white and full black.
No detail in any gray areas.

Also cleaned the bearings and bushings (what fun!) No change.

Also ran a long extension cord to clean power .. no change.

Damn.. I've got some good ideas to try out, but not with that pattern!

Thanks for the suggestions

[Richard Rumancik]

Chuck - I didn't look at this thread until Andrea linked to it - it helps draw attention if the title of the post is more specific . . .

Have you made any progress since the last post? I assume the project is “done” but you probably still want to figure it out for future reference. This situation is a bit confusing and I am trying to get my head around it as well as understanding some of the responses. I really don’t think it is a motor, banding, power or bearing problem. It is an issue of selecting the appropriate conversion from g/s to b/w, and then setting the driver correctly.


Rodney .. I'm not actually using the 3D settings . . I'm running it in Black and White mode, and I've assigned 16 levels of power/speed combinations. I'm getting an OK 3D effect with a heavily modified grayscale image run in RGB mode . . .

Since you are using B&W Mode, how are you using 16 mapped power/speed settings? To me, these are mutually exclusive. To use the 16 mapped settings, you must use Manual Color Fill. The Manual Color Fill Mode is intended to allow 16 different settings for raster and vector combinations. (Color Fill is a bad term. It should have been called color mapping.)

When you say you are using 16 settings, what exactly do you mean? The 16 settings are normally for use with the Mercury color palette, not 16 shades of grayscale. Did you assign a grayscale palette? (I saw a post where someone did this, but haven’t figured out what actually happens in that case.)

The image should have an appearance something like the Porsche image attached. You need a solid black background, with the “high” areas completely white and lower areas increasingly darker shades of gray. Does your raw grayscale image have an appearance somewhat like this?

Are you sending the grayscale image from PhotoShop to the driver using B/W mode? Or do you convert it to b/w in PhotoShop first?

I started a longer post but decided I would ask these questions first instead of rambling on.

[Rodne Gold]

If you use greyscale then the whole thing is converted to a halftone image and is not the same as vector based fills unless you use the colour mapping function in the GCC driver (kinda like a colour substitution)

[Dan Hintz]

I really don’t think it is a motor, banding, power or bearing problem. It is an issue of selecting the appropriate conversion from g/s to b/w, and then setting the driver correctly.
Agreed....

[Chuck Stone]

Since you are using B&W Mode, how are you using 16 mapped power/speed settings? To me, these are mutually exclusive. To use the 16 mapped settings, you must use Manual Color Fill. The Manual Color Fill Mode is intended to allow 16 different settings for raster and vector combinations. (Color Fill is a bad term. It should have been called color mapping.)

When you say you are using 16 settings, what exactly do you mean? The 16 settings are normally for use with the Mercury color palette, not 16 shades of grayscale. Did you assign a grayscale palette? (I saw a post where someone did this, but haven’t figured out what actually happens in that case.)

That might have been me. Yes, I created a new palette and assigned the
power levels to each shade. I left the speeds alone. (this is complicated
enough as it is .. reminds me of building color profiles for printers)

Then again, it is possible that the driver is ignoring my palette and doing
(on it's own) what I think I'm telling it to do.



The image should have an appearance something like the Porsche image attached. You need a solid black background, with the “high” areas completely white and lower areas increasingly darker shades of gray. Does your raw grayscale image have an appearance somewhat like this?

Yes.



Are you sending the grayscale image from PhotoShop to the driver using B/W mode? Or do you convert it to b/w in PhotoShop first?


I'm sending an RGB file from Photoshop to the driver. The image is gray,
black, white but no other colors. In the driver, I've
loaded my own MER file (grayscale palette) and I've changed the parameters
several times. I've tried it in B&W mode, Stamp mode, 3D mode and then
tried the manual fill. So far they all worked about the same except for
the manual fill.

I have no trouble getting different depths, getting that 3D (or 2.5D?) effect,
just that there is this cross hatch pattern in the background that I can't
seem to get rid of.

BTW this is 100% raster

[Richard Rumancik]

Chuck, I'm a bit confused . . . you are obviously getting output, but are you really sending a xxxx.rgb file to the driver? Although it does output something, I did not see anywhere that an RGB file is a "legal" input to the Mercury driver. The fact that it is actually doing something is interesting, but the fact that it is not what you want makes me think you should back up and try the standard alternatives. Personally, I think it must be reading the info in the RGB file, misinterpreting it as standard grayscale values, and then using the driver B&W mode on-the-fly conversion to halftone it. If it is dithering both the black and the white, then something is certainly being misinterpreted.

A lot of people use CorelDraw as the interface to the laser - a few use Illustrator. I've never tried to bypass CorelDraw - even if I have a bitmap-only file I still embed it into CorelDraw to provide my position info. And usually I have raster and vector mixed, even if it is just fixturing or reference info. So I need to use CorelDraw pretty much 100% of the time.


. . . I created a new palette and assigned the power levels to each shade. I left the speeds alone. . . . Then again, it is possible that the driver is ignoring my palette and doing (on it's own) what I think I'm telling it to do.

I'm leaning toward it ignoring everything past color #1 as I still think that in B&W mode, the only setting that is used is the setting for black.

Your new palette would probably work properly for vector images that have 16 shades of gray in discreet patches. I don't think it will map to a setting on a pixel-by-pixel basis. To map pixel-by-pixel, they created the 3D option. Which is very slow by comparison as you are not just turning the laser on and off. Also, with 3D mode it will use 200 shades of gray, not 16.

If you want to test further, you could try to create a grayscale bitmap in PhotoShop (bmp or tif I suppose). Then convert this to b/w 1-bit using your favorite conversion method (Stuki, Jarvis, Floyd-Steinberg, etc.) At this point, the black background should be 100% black. (It might look odd on the screen - the representation in Corel often does not look promising.) Then send the b/w file to the driver using Manual Color Fill mode. Set the parameters for "black" and see what happens to the background.

I think that because your work flow and file is unusual, the suggestions that everybody is making might not really help or be applicable to your situation. You might be able to get it to work, but it seems like you are in undocumented territory. And the manufacturer won't help if you are doing something unusual. (When I bought my laser I was told it would accept AI and AutoCad files - but it was impossible to get any support on anything other than the latest version of CorelDraw.)

Maybe try to give the driver what it is expecting and see what pops out. You could also re-try the 3D mode on the same file and see the result.

[Chuck Stone]

I usually use the 3D option unless I'm doing something like engraving a name.
Then the B&W is fine. But most of what I do is more involved than that. I've
tried the B&W because people have mentioned trying different options in it.

The 3D mode might use more than the 16 levels in my palette, but I assume
(dangerous word, that!) that if I'm specifying 16 of them, I'm at least setting
parts of the range, and the software will take care of the rest, keeping the
extra levels in between the ones I have specified.

And you're right .. I'm probably not doing what the manufacturer would
expect. I've been in that position before with other manufacturers, other
products. . One ended up hiring me to write manuals on how to do it, then
they hired me to teach. (this was after they said 'can't be done' .. I quickly
found out that 'can't be done' is corporate speak for "We don't know how,
so we're not supporting it".
I don't mind trying things

I had to stop trying things on this one so I could document things a little
better. Then found that my camera died, so I can't even send pics.

What I know so far is that this happens in all modes, but it is most
noticeable in solid colors. Darker colors show it better. Higher DPI makes
it more pronounced and changes the spacing.

It seems like the power is cycling somehow .. ramping up and down across
the length of the axis. There's three separate patterns going on.

The obvious ones are along the X and Y axis, looks like a screen pattern.
Nothing I do changes this pattern except for the density. Higher power
makes it more noticeable.

The third one is a bit more interesting. It forms 'rolls' along the piece, but
not parallel to either axis. So the power is ramping up and down as it travels.

Since the camera doesn't work, I tried to draw it out. Call me Picasso.
Hatch1.jpg shows what it looks like with heavy patterns.
165081

Hatch2.jpg shows the background pattern that's not in line with the laser
beam travel, but shows the power ramping.
165082

Hatch3.jpg shows what it would look like from the side of the piece..
as if it were cross-cut.

165083

I don't expect tech support here, just thought you might like to see it
and if anyone has idea or even WAG's I'd be interested in hearing them.

ps.. I did try the 1 bit B&W file, just got less resolution/detail than using the
RGB file. As I understand it, the B&W mode will interpret the grayscale by
changing the spacing of 'dots' to achieve the look. The 3D mode will change
the power of the beam in that spot so rather than change the number
of dots, it changes the depth of the cut. At least, that's how I THINK it works..

[Mike vonBuelow]

Chuck, since I'm in the same boat (http://www.sawmillcreek.org/showthread.php?t=150316) as you, do you have a file that has worked without the hatch?

This is agonizing!

[Chuck Stone]

Chuck, since I'm in the same boat (http://www.sawmillcreek.org/showthread.php?t=150316) as you, do you have a file that has worked without the hatch?

This is agonizing!

No .. I've never had it not do that. (except for files that didn't have enough
engraved area to show it.. but it was probably there anyway)
I do notice it is less intense at lower DPI but that's because the depth is
less. If I make a second pass, the effect is additive.

No idea what it is, and no answers from GCC.