My JPG image has a pure white back ground [update: I only thought it was pure white. It was supposed to be, but CorelDRAW has a problem, see below, starting with @artistseth’s post here, and my reply below it.]:
At first I thought maybe the JPG file had pixels outputted from CorelDRAW that were slightly less than white, maybe a little gray, as a result of JPG compression (aka artifacts), and that this was being magnified by LB, so, even though an inspection of the JPG did not reveal JPG artifacts, still I outputted a PNG file instead, which got the same result.
Finally, I switched the Image Mode from “Dither” to “Threshold”:
Overall, I’m glad I found a workaround, but this seems like a bug or glitch, as the LB program is outputting dots where there are no dots in the source file.
A quick Google turned up this. It relates to color images with a limited pallet, but I think the algorithm may monkey with B/W images too. Bold is mine…
simulate shades that aren’t available in the limited palette, resulting in a smoother appearance and preventing harsh banding, especially when reducing an image’s color depth; essentially, it adds a controlled amount of “noise” to the image that the human eye perceives as a blended color.
You were correct. The circular portion of your image is using a 99% white. I will post it with the pure white removed. Everything remaining is only 99%, and is being dithered.
You are correct! This “moves” the software issue from LB to CorelDRAW. I just checked my source work in CorelDRAW, and the default color palette is CMYK, but the real problem is that a CMYK value of 0,0,0,0 has its corresponding RGB value set not to 255, 255, 255, but rather 254, 254, 254, thus a very very light gray, but not pure white. This is very frustrating to me, but at least you helped me find the real culprit here.
And as a final note on this, in CorelDRAW, going to Tools > Color Management, and switching the default color palette from CMYK to RGB, means that clicking White in the palette to apply a fill, results in a pure white, 255, 255, 255, which then corresponds to CMYK of 0,0,0,0 — which is what I would have expected to happen when going the opposite direction (from CMYK to RGB) as well. But now I’m on a default that works as I would have expected! Learn something new every day.
Also fyi, since “threshold” only works for images you want to posterize, issues similar to this can usually be resolved by increasing the “contrast” setting, which pushes the 99% white up into the pure white range.
