Photo engraving glitch! Need help!

[Bill Stearns]

Hi ALL
I’ve been engraving peoples’ personal photographs for years; have suddenly run into a glitch!
After Photo-shopping a colorized picture ‘way I want it, I’ve typically turned it into a grey-scale bitmap. (8 bits?) - so that my PhotoGrav software would recognize it.
I read somewhere on SMC, ‘while back, the suggestion of converting photos to “black & white”, instead of grey-scale - which, then, seems to allow for 16, or 32, bits. (I believe?) In choosing ‘black & white’, photos seemed to engrave much nicer; clearer - mostly, on my Alder wood plaques.


Now, I’m engraving a photo on solid black granite. Have placed the (dog’s) photo on a black background - necessary when using my PhotoGrav “granite setting”. (BTW: I’m using CorelDraw X5.)
Appears the photo will engrave nicely, but surrounding the photo, I’m seeing horizontal lines of very tiny “dots” repeating throughout the black background! Imagine it’s something simple I’m doing wrong. What do I need to adjust, or do in order to eliminate those dotted lines? Help!

Thanks in advance! and have 'great day!
Bill

[Kev Williams]

Nope, you're doing nothing wrong, and you've likely been having this happen with every 2-color photo- but you've never noticed it. You're now essentially engraving in negative on black with the engraving white, which is showing up vividly against the black. The reason for the dots is because the background isn't truly black (or white), it's more like 99.9% black (or white) and the dots represent the .1% of the opposite color.

The only fixes I got are:

try lighten the background to as close to 100% transparent as possible. One way is to raise the contrast, but that changes the whole picture. Another way is to cut away all the background from the photo leaving 'nothing', but even doing that I've still had dots engrave. Yet another thing to try is to open the pic on screen, if the pic has a white background, invert the color, then look for white specks within the now black background, either erase the specks or paint them black.

If that doesn't work-- Place the pic in Corel, lock it, then just use the pen and draw around where you'd like the outer boundary of actual engraving to be. Once drawn, take a piece of thin cardboard (postage boxes are great), cut it the same size as the granite, and then cut the boundary into it. Place it over the granite and engrave, and the cardboard will eat the errant dots rather than the granite :)


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[Bill Stearns]

[QUOTE=Kev Williams

Hi, I appreciated your suggestions - thanks!
Seems to me, nothing is more frustrating than to solve a problem and, later, not be able to remember how you did it! (Will definitely add your suggestions to my “how-to” file.)
Tiny lines of “dots” showing up on my black granite photo engravings: seems, in this case, had to do with my choice of “dithering” with CorelDraw: I simply changed from the “Floyd” setting to “Jarvis” setting. The surrounding dots disappeared!


I should’ve taken the time, ‘long time ago, to better understand “pixel-ratios” and difference ‘tween “grey-scale” versus converting photos to “black ‘n white”. - 'cause they really do turn out nicer looking! Maybe, somebody can provide a concise, easy-to-understand explanation regarding the advantages of this? Oh, so much to learn, so little time, uh? Thanks ‘gain!

Bill