Coreldraw - import eps export png gives dithering of black and white

[john banks]

I started up Coreldraw X5 (using RGB or CMYK) and imported an eps file which has one layer and which shows using the color picker as CMYK values of 0,0,0,100 or 0,0,0,0, and looks black or white on the screen. When I export it as a PNG or GIF to make something to raster engrave, it changes the black to a gray level of 46 and 254. This means that when saved as a black and white PNG or GIF that the blacks and whites are both dithered. If I save it as a black and white BMP it is fine.

There is something I'm not understanding about the way the color profiles work as I am new to CMYK and always worked with RGB in programming work. I can save as a BMP no problem, but wondered what is going on? I think the eps source file is CMYK and that means that black and white are not black and white in the RGB sense (ie 0x000000 or 0xffffff), but wonder if there is an easy fix other than saving as BMP?

Attached are the preview boxes zoomed in when saving as PNG showing the intended appearance when saved as grayscale (even though it is showing a gray level of 46 instead of 0 for black, and 254 instead of 255 for white) but not when saved as black and white.

If the source material is vectors which are monochrome with areas of fill and I want to engrave, then I don't really want dithering going on I don't think as I want the crispest edges I can using very high resolution. As it happens, engraving the dithered image on wood looked just fine.

[Dan Hintz]

You're converting between color spaces (CMYK versus RGB), and that's the heart of the issue... a color in CMYK does not directly map to a color in RGB (multiple colors in CMYK map to a single RGB). While one would think "black" (i.e., CMYK) would map directly to 0x000000 in RGB, it doesn't necessarily work that way.

Once you've opened the image, convert to RGB, then before saving to your BMP format, convert to a monochrome image. That should prevent the dithering.