I was playing around doing a photograph on some black marble...I haven't done a photograph in a while. Anyway, I noticed that at very regular intervals (about ever .25 inches) the engraving is darker. So you can see some pretty clear horizontal banding...does anyone know if this is an adjustment I need to make or what?

Mike

Did you convert the photo to dots via PhotoGrav or one of the other methods (ie: converting to "bitmap" in Photoshop or to "B&W in PhotoPaint)?

If so, did you scale the image at all after the conversion? This will cause banding.

Dave,
I did convert and use PhotoGrav but I don't resize or anything after importing back in. When I was showing the banding I was sending to the engraver at 600 DPI. I sent it again at 1200 DPI and didn't see the banding...of course then it took a lot longer...

Mike

Did you print it from CorelDraw, placing the photograv output into a page in CorelDraw? If so, when importing the bitmap, did you simply click the cursor to place the imported file in Corel? You didn't drag the cursor to size it in Corel? Or use the handles to stretch or scale the image in any way?

Was the file you ran in and out of Photograv a 600 or 300 dpi image? The dpi that you run through Photograv should be the same as the dpi setting you set the laser to, or an even division (ie: 600, 300, 150, etc... for lasering at 600). For example if you run a 400 dpi image through Photograv it will probably have banding at a laser setting of 600, but not at 1200.

I didn't resize at all once back in Corel X3. I also saved and PhotoGrav'd at 300 dpi then engraved at 600. Very noticable banding at 600, only a slight banding (but still noticable) at 1200dpi.

Mike

Mike,

I've been able stop banding like that by lowering my speed & power settings.

On my Epilog 24TT 35W, I run 80% speed and 30% power on Laser Sketch marble now....no banding. My previous speed of 100% produced banding similar to what you're describing.

HTH,

Cody

Cody,
Thanks, I'll try that...I was using 100 speed and 60 power...I'll slow it down a bit and see what happens.

Mike

Cody,
I tried to slow it down and am having the same banding effects. I think I remember somone a while back talking about adjusting the tension on some belts...I'll try to look into that.

Mike

Mike,

Here's a goofy question: Is the banding appearing on your screen before you send it to the laser? My old scanner started putting bands in my scans, but they were hardly noticable....until they were engraved. It only took me once to figure that part out.

I was sure hoping that slowing your speed would help, as that's one of the easiest things to control.

Cody

Mike, Try reducing power not speed. Reducing power works for me.

Kurt

If it is something like 1/2" darker, 1/2" lighter, 1/2" darker, etc., it is caused by bitmap misinterpretation.

The techniques you posted seem to be right. I assume when you went to 300 DPI resolution you did it by resampling. If you went there then resized it could be problematic.

Also Corel 9 likes the image to be a size that the pixels in the width are divisible by 4 evenly. There is also a bug in 9 that required you to remove 1 pixel of width from the image after all other adjustments, in order to not get a line vertically down the center. (Since the updated ULS driver a few years ago this has not caused me problems.)

Philadelphia, PA (Really Bensalem)

When you finally understand it completely... it changes.

Thanks to Brian at Epilog helping me narrow down my problem, I finally figured it out. When I was exporting my file to the 8-bit grayscale, the icc profile and anti-aliasing buttons were checked. I'm not sure which one of these fixed my problem, but it's good now! Anyone know what these do?

Mike