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Color translations

PostPosted: Sat Jan 30, 2016 5:35 am
by AdPrinter
I encountered a problem tonight, with MeshCAM Art version 4, that I really can not comprehend how such a thing is even possible.
I had created some artwork in Corel Draw, which I exported in Portable Network Graphics format, using only three colors. When I opened the file in MeshCAM Art, and entered the X size, clicked on the "Allow Re-size" option, and changed the resolution from the 300 dpi (which was the resolution used when the file was exported from Corel) to 100 dpi, the file opened, with 32 shades of blue instead of the three colors used. Unhappy with this, I closed the file, and tried to again open (the same file- no changes at all), with the only difference being that I changed the resolution from 300 dpi to only 90 dpi. The file opened, with the original 3 colors used. WHY? What could have possibly caused this to happen? (I.E. the change from only 3 colors to 32)? And how could image resolution possibly even affect the number of colors imported into MC Art, when the same exact file is imported, unaltered? This defies all logic to me, and had me fit to be tied, after the struggle! Can anyone explain this?

Re: Color translations

PostPosted: Sat Jan 30, 2016 6:45 pm
by Randy
Robert is the only person on the planet with knowledge of the inside workings of MeshCAM, so he would be a good candidate. :)

My guess would be some dithering side effect from the scaling routine when MeshCAM adjusts the DPI (it will be generating new pixels from ratioing adjacent pixels from your input file). But that is just a guess.

Does Corel Draw generate a tranparency layer when it exports PNG? That might be a factor also.


Re: Color translations

PostPosted: Sat Jan 30, 2016 11:02 pm
by AdPrinter
Your guess "some dithering routine" is probably the culprit. It is literally the only thing that makes any sense. As far as Corel Draw outputting a transparency layer, I simply do not know. CD has many options for controlling the export of artwork. Which includes a check box for NO Transparency. But it also supports many different color options, and file formats, etc. The program really tries it's best to be all things to all users. And actually does a pretty good job of it, most of the time. Whether one is importing artwork into the program, or exporting artwork from the program. The options are almost unlimited. And with this level of variables, it makes it very difficult to determine exactly what to do, to correct problems when they arise. Other than multiple trial and error sessions, until something is found to work. But the experience I went thru the other night, well I said it before "I was fit to be tied!", because literally the only change I made, was in the file's resolution, when opening the file into MeshCAM Art. (This, after having already gone through MANY trial and error sessions of color option changes, and file export options, in all of their various permutations) finally working with the resulting file, changing ONLY the resolution at the time of opening it into MC. So this experience has taught me, for all future sessions, to keep the resolution as low as possible- IF one wants to preserve the numbers of colors in the image!
Have a blessed day!