Technical Library: Resolution and How it Affects Your Engraving

1)

Uses for different resolution settings:

75 - 150 - 200 DPI - These resolution values are typically used for non-production purposes where you want to experiment with image location, or if you want to quickly produce a rough draft.

300 DPI - This resolution can be good for production work where image quality needs to be good, but not great. Many users will use 300 DPI on plastic and other materials that don't require a lot of power in combination with large block lettering. Attempting to produce really fine detail with 300 DPI is not recommended.

400 DPI - This resolution value is ideal for many applications. It combines very good image quality with fast engraving times. Many users like 400 DPI for all of their work.

600 DPI - When really fine detail or overall excellent results are required, most users choose 600 DPI.

1200 DPI - This resolution is used for projects that require the best engraving quality possible, although it's seldom used because under normal circumstances most people cannot visually discern the difference between 1200 and 600 DPI. There are however some users that appreciate this high level of quality and are willing to take twice as long to produce an image at 1200 DPI as it would take them at 600 DPI.

The diagram below shows the concept of raster lines and dots per inch (DPI). The arrows show the change in direction of the carriage between raster lines. The difference in dot density between 300 DPI and 600 DPI resolution is shown. Notice that the spot size did not change. The only way to change the spot size is to change the focus lens.

2)

There are several things worth noting:

• There are four times as many dots engraved at 600 DPI than there are at 300 DPI - twice as many horizontally and twice as many vertically.
  
• The gap between the dots is greatly reduced at 600 DPI. At 300 DPI the lesser overlap is responsible for the jagged edges that are visible when engraving at lower resolutions. It's important to remember that while resolution plays a part in producing good image quality, the artwork that is sent to be engraved is just as important. If the artwork that is sent to the laser is poor quality, trying to engrave it at 600 DPI will not improve it. It's always best to start with high resolution images. Poor artwork will probably always look poor at any resolution, while good artwork will look good at any resolution.
  
• Twice as many dots and twice as many lines at 600 DPI produces a much deeper burn into materials like wood than you would see engraving the same image at 300 DPI. This is important to understand because depth of burn is closely associated with engraving resolution - the higher the resolution, the greater the depth of burn for a given speed. The relationship between resolution, depth of engraving and Speed and Power setting is something that most people figure out with just a little experience. The Epilog manual helps to make this easy to understand by providing different Speed and Power settings for 300, 400, and 600 DPI engraving for each different material listed.
  
• Changing resolution does not change the spot size. Resolution only changes the spacing between dots. For most applications, simply increasing the resolution is the preferred method of improving image quality. For more demanding applications it's necessary to change resolution and spot size (focal length).

3)

The photos below show a CorelDraw clipart image engraved using a 2.0 inch lens at 300 DPI (top) and the same image at 600 DPI (bottom). This clipart image is full of different shades of gray and you can see that the dot spacing is quite spread out on the 300 DPI. Just changing the resolution to 600 DPI produces so much dot overlap that the fill patterns tend to blend together much better. It's a matter of personal preference as to which resolution looks better, but these photos show the dramtic difference resolution can make, especially when engraving with grayscale images.

The other important aspect of changing resolution is engraving time. The 300 DPI image took 4:05 minutes to engrave and the 600 DPI image took exactly twice that long (8:09 minutes). Because of the nature of the material (plastic) we were able to run the job at the same speed for both 300 and 600 DPI. As mentioned earlier, there are twice as many lines at 600 DPI as there are at 300 DPI so you would expect the time difference to be twice as much. This effect will always be evident on materials (like acrylic, coated metals, plastic, etc) that don't require much power. When you start engraving into materials that require a lot of power (like wood), you will find that running a job at 300 DPI will produce a good image, but you will not get as much depth as you do at 600 DPI. You will find that in order to get adequate depth in wood at 300 DPI you will need to slow the laser down and typically the time difference between 300 and 600 DPI is not so great.