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percentage fills in PDF cause color palette to change

pejotu
Participant
Hi!

I tried to use percentage fills (50%) to create an easy shadow effect for a plan drawing, and noticed that the color palette on my PDF-files became altered after adding them.

After a long series of tests I've come to the conclusion, that having even one percentage fill with a transparent background pen in a drawing causes the color palette to shift.
Is this a known bug, and is there a solution for it?

(attached two PDFs of the same fills - one with opaque background color, one with a transparent background color)
8 REPLIES 8
Thomas Holm
Booster
pejotu wrote:
...(attached two PDFs of the same fills - one with opaque background color, one with a transparent background color)
I take it you mean that the printed/displayed color of these finished composite fills shift, not the pen set itself.. could you please elaborate a little?
AC4.1-AC26SWE; MacOS13.5.1; MP5,1+MBP16,1
Anonymous
Not applicable
pejotu wrote:
..After a long series of tests I've come to the conclusion, that having even one percentage fill with a transparent background pen in a drawing causes the color palette to shift.
Is this a known bug, and is there a solution for it?..
The percentage fills work by simply changing the ratio of foreground coloured pixels to background coloured. At 50 percent, every other pixel is transparent. The eye sees this as a lightening of the shade, the same way mixing white paint with a darker paint produces a lighter shade.

The only way to get a solid to match a transparent it is to use a different darker shade for the semi-transparent fill. When lightened it will appear a similar shade to the solid.

When applying it to floorplan shadows, I've have found a uniform dark grey with 25% solid works quite nicely and doesn't distort any underlying colours too much. (i.e. a darker colour with greater transparency looks better than a lighter shadow with less transparency.)

If you're still having problems, post up an image of the problem and we'll try to help further.
pejotu
Participant
Hi

Mmm, I guess I'd expect the color of a 50% fill color to change, when it's applied at 50% strength, but this was not my point.
Apparently my second attachment with the unchanged colors didn't get through - I'll try to post a new one tomorrow.

But really the point was, that when I have a fill with a 50% percent fill anywhere in the drawing, all the colors (including solid fills and all) on the resulting PDF will become noticeably darker.
When I create the same PDF using Adobe's PDF-printer, the colors are preserved...

Well, I'll return to this tomorrow,
.p.
Anonymous
Not applicable
Sorry I didn't get the problem earlier, but I think I understand your problem now. You are saying when you produce a pdf from a drawing which only has one fill with a transparent background, all of the other fills appear darker.

In addition to the second attachment, a few questions may help us -

What version of ArchiCAD - 9,10,11,12?
What operating system?
How are you producing the PDF where you notice the problem? Are you printing to another PDF driver (i.e. Amyuni or CutePDF), or are you 'Saving-as' a layout (in AC11+12) or I believe OSX has PDF production built in.

After a quick test in AC12 I can't see any problem with printing to Amyuni PDF driver or 'Saving as' methods with respect to other colours changing.

What I did notice was that only the 'Save as' method produces proper transparent percentage fills. Printing to Amyuni only produces an opaque dotty mess with no colour, whilst CutePDF produces a dotty transparent hatch. This is probably not related to your problem though, other than proving not all PDF printers are equal!

And yes, as you have found out, you can only attach one attachment per post.
pejotu
Participant
Hi!

Here's a PDF with four test pages.
Done with Archicad 12 Finnish, R2325, Windows XP.

The graphic has 6 squares, with the upper row set to 50% fill with a transparent background pen, the lower squares are the same color with a 100% fill. Above these are three lines using the same pens.


Page
1) Save As PDF from Archicad

2) Save As PDF from Archicad, the top middle square with opaque background pen.

3) Save As PDF from Archicad, the top row all with opaque background pen.


Page 3 has the correct colors, pages 1 and 2 (with transparency) show the darkened, shifted colors.
A Print to PDF via Adobe PDF printer will also result in correct, transparent colors, but as mentioned earlier in this thread the quality is poor because of the dithering. Also the resulting file size too big to include as attachment here...

.p.
Anonymous
Not applicable
Well spotted! It produces an incorrect result on mine also. Maybe submit it to your reseller as a bug?
Anonymous
Not applicable
Also attached is a screen shot of the desktop showing the original colours.
Thomas Holm
Booster
You should be aware that this might not be a Graphisoft issue, it might just as well have to do with how Adobe Reader renders transparency. The difference is subtle enough. I've had similar issues when comparing printing from Adobe Indesign and from same-generation Reader.

I seem to recall a warning in one or the other of Indesign's export dialogs, that issues might appear because Reader doesnt' render transparency correctly, it instead tries to imitate it by mixing pixels and colors some way.

I think a slight hue shift is more than likely to happen in this situation.
AC4.1-AC26SWE; MacOS13.5.1; MP5,1+MBP16,1