Steven Cox
03-21-2012, 10:35 PM
The Rastus filter will convert a Greyscale image to a one bit halftone image and this is what's needed for most of the chinese lasers out there because these lasers can't process a greyscale image.
Since my other posts about Rastus, I been requested via PM's to share some notes. You could apply some of this to other halftone filters and it may work OK. As pointed out by others on my previous posts, this is not the only way to convert images - there are other methods that may work equally as well. So following are my notes on using the Rastus filter for what I've found that works for me.
If you are unfamiliar working with images, then this is something you'd need to learn because the old addage crap in crap out really applies here. Whilst it's possible to output low resolution images for laser engraving, a higher resolution image in my opinion should produce much better results. As long as you follow the basic rules of image conversion you should be able to get acceptable results. The one golden rule I follow is that you can Reduce an image to gain DPI but you should not enlarge it.
For best results the image should be at the physical print size in Greyscale at 300 DPI or better. For laser engraving, I find clipped images work best or images with minimal background. If you aren't that good at clipping there are some services online that will do it for about $15 each overnight. I've used these services myself because at $15 sometimes when I flat out, my time is better spent on other things. I usually dedicate about an hour just to the clipping process and charge my customer for artwork at generally a minimum of $30. This is one of many clipping services out there artviper.net/photo-retouching/image-clipping-service.php or google "image clipping service" for more. The conversion process after an image is clipped or prepared only takes a few minutes.
If you use a clipping service, send them your colour image tell them you want it clipped with basic retouching and you need it at 300 dpi as large as possible for gloss printing. This way you'll get back the best possible image that you can use for almost anything. When you get it back convert it yourself to Greyscale and reduce it's physical size to what you need, then follow the tips below. Note, when an image is professionally retouched you rarely need to sharpen it but for laser engraving you may still need to adjust brightness & contrast. It really depends on the image as to what's needed, my notes on Rastus are based on images taken from a digital camera usually from the customer. General rule is that if it looks too dark on screen then you'll need to adjust it.
Here's how to do it In photoshop, you can also do this in Corel's PhotoPaint and the Rastus pluging should work in most versions. The commands below are similar but not the same (you'll work it out).
Again: A clipped image loosing the background seems to work best.
STEP ONE
If Image is not very Sharp this first process helps define the image edges.
1. Open the image
2. Duplicate the image Layer, with the duplicated layer selected in Layer Manager Go to: Filters > Other > Hipass
3. Set the Pixel Value to 20 (20 seems to work best) then click OK
4. Back in the Layer Manager change the Dropdown from Normal to Soft Light (depending on the image you could also use Hard Light). If you toggle the layers view icon in the Layer Manager you'll see the difference.
5. Now merge the two layers together: Layers > Merge Visable
6. At this point you should save the image in case you want to use it again but don't overwrite the original, save it as a new image.
STEP TWO - Convert to Greyscale and Image Adjustments.
1. Convert to 8 bit greyscale Image > Mode > Greyscale If prompted to flatten the Image, choose Flatten.
2. Important: Resize the image to the physical size its going to get engraved at (that is X inches by Y inches). Whilst the image should be at least 300 DPI a lower resolution image may still work, because the Ratus Filter at step 3 will set the final Output DPI. After sizing the image Don't resize the physical size in anyway if you need another imager smaller or larger make a new one to the size you want.
3. Bump up contrast and brightness about 25%. For laser engraving reducing the grey areas works best. If however the image is very dark or has a background of dark areas, then try a Brightness of 75% & Contrast at 50%. Image > Adjust > Brightness & Contrast
4. Use the unsharp mask to help exaggerate the edges. This is importantant for most laser engraved images. Image > Filters > Sharpen > Unsharp Mask Set at 250% with a Radius of 3 pixels and Threshold = 0
STEP THREE - Now the image is ready to send to Rastus.
1. To convert the Image using the Rastus plugin select File > Export> Rastus
2. Set the Output DPI to 300 (Increase the DPI for a finer print, generally 300DPI in my testing seemed to work best).
3. Deselect Bilinear Interpolation. (We don't need better quality for Laser Engraving)
4. Set Scale to 100% (Default Setting)
5. Set File Format to TIF
6. Click OK
7. Save the File with .tif Extension in the desired location Example: abc_image.tif The Saved file will then save as abc_image.Gray.tif
Adding the .tif to the file name is important because despite setting the file format to TIF, Rastus doesn't add the extension to the file name, it's the only bug I've found.
6. Import the Rastus converted bitmap into CorelDraw to laser engrave, remember don't resize it in any way.
For Pine on my 60 watt laser I used Laser Settings as: 300 Speed 40% min Power and 50% Max Power. You will need to experiment with settings for different woods.
To all interested I hope you find this info useful and I'm happy to answer any question you may have, if and when I can.
Regards Steve.
Since my other posts about Rastus, I been requested via PM's to share some notes. You could apply some of this to other halftone filters and it may work OK. As pointed out by others on my previous posts, this is not the only way to convert images - there are other methods that may work equally as well. So following are my notes on using the Rastus filter for what I've found that works for me.
If you are unfamiliar working with images, then this is something you'd need to learn because the old addage crap in crap out really applies here. Whilst it's possible to output low resolution images for laser engraving, a higher resolution image in my opinion should produce much better results. As long as you follow the basic rules of image conversion you should be able to get acceptable results. The one golden rule I follow is that you can Reduce an image to gain DPI but you should not enlarge it.
For best results the image should be at the physical print size in Greyscale at 300 DPI or better. For laser engraving, I find clipped images work best or images with minimal background. If you aren't that good at clipping there are some services online that will do it for about $15 each overnight. I've used these services myself because at $15 sometimes when I flat out, my time is better spent on other things. I usually dedicate about an hour just to the clipping process and charge my customer for artwork at generally a minimum of $30. This is one of many clipping services out there artviper.net/photo-retouching/image-clipping-service.php or google "image clipping service" for more. The conversion process after an image is clipped or prepared only takes a few minutes.
If you use a clipping service, send them your colour image tell them you want it clipped with basic retouching and you need it at 300 dpi as large as possible for gloss printing. This way you'll get back the best possible image that you can use for almost anything. When you get it back convert it yourself to Greyscale and reduce it's physical size to what you need, then follow the tips below. Note, when an image is professionally retouched you rarely need to sharpen it but for laser engraving you may still need to adjust brightness & contrast. It really depends on the image as to what's needed, my notes on Rastus are based on images taken from a digital camera usually from the customer. General rule is that if it looks too dark on screen then you'll need to adjust it.
Here's how to do it In photoshop, you can also do this in Corel's PhotoPaint and the Rastus pluging should work in most versions. The commands below are similar but not the same (you'll work it out).
Again: A clipped image loosing the background seems to work best.
STEP ONE
If Image is not very Sharp this first process helps define the image edges.
1. Open the image
2. Duplicate the image Layer, with the duplicated layer selected in Layer Manager Go to: Filters > Other > Hipass
3. Set the Pixel Value to 20 (20 seems to work best) then click OK
4. Back in the Layer Manager change the Dropdown from Normal to Soft Light (depending on the image you could also use Hard Light). If you toggle the layers view icon in the Layer Manager you'll see the difference.
5. Now merge the two layers together: Layers > Merge Visable
6. At this point you should save the image in case you want to use it again but don't overwrite the original, save it as a new image.
STEP TWO - Convert to Greyscale and Image Adjustments.
1. Convert to 8 bit greyscale Image > Mode > Greyscale If prompted to flatten the Image, choose Flatten.
2. Important: Resize the image to the physical size its going to get engraved at (that is X inches by Y inches). Whilst the image should be at least 300 DPI a lower resolution image may still work, because the Ratus Filter at step 3 will set the final Output DPI. After sizing the image Don't resize the physical size in anyway if you need another imager smaller or larger make a new one to the size you want.
3. Bump up contrast and brightness about 25%. For laser engraving reducing the grey areas works best. If however the image is very dark or has a background of dark areas, then try a Brightness of 75% & Contrast at 50%. Image > Adjust > Brightness & Contrast
4. Use the unsharp mask to help exaggerate the edges. This is importantant for most laser engraved images. Image > Filters > Sharpen > Unsharp Mask Set at 250% with a Radius of 3 pixels and Threshold = 0
STEP THREE - Now the image is ready to send to Rastus.
1. To convert the Image using the Rastus plugin select File > Export> Rastus
2. Set the Output DPI to 300 (Increase the DPI for a finer print, generally 300DPI in my testing seemed to work best).
3. Deselect Bilinear Interpolation. (We don't need better quality for Laser Engraving)
4. Set Scale to 100% (Default Setting)
5. Set File Format to TIF
6. Click OK
7. Save the File with .tif Extension in the desired location Example: abc_image.tif The Saved file will then save as abc_image.Gray.tif
Adding the .tif to the file name is important because despite setting the file format to TIF, Rastus doesn't add the extension to the file name, it's the only bug I've found.
6. Import the Rastus converted bitmap into CorelDraw to laser engrave, remember don't resize it in any way.
For Pine on my 60 watt laser I used Laser Settings as: 300 Speed 40% min Power and 50% Max Power. You will need to experiment with settings for different woods.
To all interested I hope you find this info useful and I'm happy to answer any question you may have, if and when I can.
Regards Steve.