DPI setting for Chinese laser

[Dieguy99]

Hey guys, My first post

First thank you all for your inadvertant help. I have spent countless hours reading past threads and have learned alot.

I have recently purchased a Redsail M-500 Laser system. It has been a frustrating few weeks but I finally have the machine up and running pretty well. The software is substantially different from my previous laser software experiences but I am learning quickly.

The main question I have deals with DPI. I am trying to do photo engraving using Photograv. I am trying to figure out how to set the DPI in the Lasercut 5.0 software? I know this is pretty common software for many of these chinese lasers. Anybody know the answer to this? Thnak you in advance,

Dieguy99

[lamicron]

The DPI is the step interval that you can find in the layer parameter setting.
if you set it as 0.5 it will 1 mm of advance in 2 steps, there you can see the lines , if you set it 0.01 or 0.005 you are increasing the "DPI" here it means that the lines will be closer and more detailed. the speed and the power will give you the deep of the engrave that in this case combined with the step interval will get the apropriate DPI

[terry32506]

Hi guys , I was wondering what the dpi would be for the numbers that are mentioned here, 0.01 or 0.005. Would they be equilivant to say about 500 and 600 DPI?


Terry

[SkipW]

glintid posted this info awhile back.

The scan gap is the distance the laser moves vertically (the Y axis) between passes. I think the Rabbit laser software expresses the distance as a fraction of a millimeter, ie. 0.1 is 1/10 mm etc. Because I am used to resolution expressed as standard numbers DPI (dots per inch), I converted mine and keep a chart near my computer. For example 300dpi is 300/25.4 dp mm which equals 11.811 dpmm. To convert it to distance between dots (passes) in mm you invert the number. So 1/11.811 = a scan gap of 0.084mm. I did this conversion for all the common usable resolutions which are 600, 500, 300, 250, 200, 150, 100, 75, 50, 40. Easier for me to remember than .084. When engraving photos, you want to use a scan frequency that is a multiple of the dot screen applied to the photo to convert it to a 2 bit .bmp file. This avoids a moire which is interference which is resultant when two lined patterns are superimposed and are out of phase. Like placing two pieces of screen material together at a slight angle.

If that seems simple, hold on to your hat. There is another variable affected by Scan Gap, power. It's actually logical. The laser spot on any material is not a crisp circle. The burn microscopically varies from material to material. It's similar to the pattern of a flashlight on the wall with an intense centre fading out to the edges. When engraving an image made of dots, the resolution is maintained by definition between the "black" zones and the unburned "white" zones. Some marerials .are inverted.

Each material is different. When the scan gap is close, the edges overlap which doubles the power at that point on the material. As the centre spots get closer, as you can imagine, the effect can be quite a dramatic increase in power. This sound efficient but in reality negatively impacts the image resolution, tending to blur it. So dependng on the burn rate of the material, you may have to increase the scan gap to get the optimum resolution. Wood for example requires a much wider scan gap than anodized aluminum.

Some brittle materials like glass, granite and marble don't burn but tend to microscopically fracture from the heat of the laser. (I think marble and granite fracture, open to correction). Anyway, if the scan gap is too close and the laser overlaps too much, the glass heats up and fractures through the area between dots resulting in a blurred, low res image. Some acrylic too tends to melt the whole surface when the dots are dense in the shadow areas and you loose resolution completely in the shadows resulting in a throw away.

These are just a few things I have learned by myself with trial and error and reading some scientific stuff on lasers and how they interact with materials. From this one realizes that laser focus and optics can make a huge difference. I have been thinking of getting an optically better (more expensive) lens for my laser to see if this in fact makes a difference to the resultant dot pattern. By the way, I experiment on plain, cheap brown card for the basic settings. It engraves quickly and holds a photographic image quite well.

[terry32506]

Hi Skip thanks for all of that information much appreciated. I am not quite clear however on the scaling so im going to ask an example question. 300DPI = 0.084mm as you stated so if I was to raise it to say 600DPI would that then be 0.084 x 2 to = 0.168? I usually convert my bipmaps to 300dpi to get as much of the 2 bits I can get. Photo lasering is a challenge indeed and much to learn.


Terry

[glintid]

Hi Terry,

I came across this post. Nice to quoted. 600 dpi means twice as many dots as 300dpi so you would halve the distance between dots (scans). So the scan gab would be .084/2 = .042

By the way, I very seldom or ever use 600dpi. First it's really slow and on most materials doesn't show. What I sometimes do is use a 250 or 300DPI screen in photoshop and engrave at 500 0r 600dpi. Trial and error I suppose; no absolute rules.

The other thing to keep in mind is, machines have 'native' resolutions. This has something to do with the increments of the drive motors and the size of each small step. There is 250/500 and 300/600. My Rabbit HX6090se engraves much better with 250/500. I'm not sure about other Chinese lasers but I expect they may be similar. Open to correction here.

Hope it helps

David

[SkipW]

Hi David,

Terry had asked about the scan gap settings and I remembered that you had posted the best explanation I've seen, so I searched your postings and found it for him.

I was just going to tell him that 600 DPI wouldn't be double the .084 setting, but half that setting, and I see that you showed up and told him that. Thanks !!!

Someone also posted steps you can take in Photoshop or Corel Photo Paint to help prepare an image for engraving. Was that you? I have to dig around on my HDD to see if I can find that. I'm pretty sure I saved the info somewhere.

Photograv is the way to go for quick and easy photo prep for engraving but if you aren't going to do it on a regular basis, it's hard to justify the cost. It's close to $400.00 I think.

Take care,
Skip

[Micheal Donnellan]

DPI = Scangap
1200 = 0.02116
800 = 0.03175
600 = 0.04233
500 = 0.05080
400 = 0.06350
300 = 0.0846
200 = 0.12700
150 = 0.1693
100 = 0.2540

25.4/DPI wanted = Scangap

[SkipW]

These are kind of basic but it's a good start. Reposted from an earlier post.

As I know there is no direct information to show how to get a good results in engraving images by using any software, but in general the concept is to convert the image to gray scale mode then black&white , or black&white directly, but the software must have a verity of options to use when converting to black&white, this can be found in Adobe Photoshop & CorelDraw, for example (Halftone, error diffusion, ordered, line art, stucki, ...).
choosing one of these methods will give a deferent engraving effects according to the pattern & number of dots produced.
the steps can be as follows:
-the image resolution should be 300dpi to get a good result
-if the resolution is less than 300dpi then rescan or resample the image
-convert the image to black&white using diffusion Dither, stucki, or Halftone method to get the best details on the engraved image.
-convert the image to black&white by any other methods to get artistic effects on the engraved image.
-every image need some fine tune before or during conversion.

Steps in CorelDraw(12 & 13):
->import the image
-> select the image
- -> select Bitmaps Menu
- -> select Mode
- -> select Black& white 1-Bit
->select conversion method [stucki] and vary the intensity

Steps in Photoshop:
->open the image
-> select image Menu
- -> select Mode
- -> select Grayscale
-> select image Menu
- -> select Mode
- ->select Bitmap
->select method [Diffusion Dither] and output 300 pixels/inch

[Prestovision]

Is photograv working on the chinese lasers

[terry32506]

Hello , I decided to not get PhotoGrav but cant see why it wouldnt work on a chinese engraver.


regards,

Terry

[SkipW]

The new ver. of Photograv (3.0) has Rabbit Lasers listed in the machine choices. There are many variables in the software that can be set by the Chinese machine owner such as resolution (.dpi), machine lens spot size, machine wattage, and max speed.

Here's what that screen looks like: http://www.photograv.com/images/ss_selectmachine.png

So yes, Photograv will work with most any Chinese manufactured laser.