The problem is that this is only an on screen issue. Any item on a screen can only fill none or at least one screen pixel. If the line is thinner than the size of your pixels it will either disappear or shown much to fat.
Other problem, only Reader and Acrobat can show all kind of PDFs correctly, even if a PDF is shown more beautiful, the correct view is only in Adobe Reader or Acrobat, all others support only a sub group of PDF standards.
If the textbook is for print, then I would check it only if it is print ok. The same problem appears on print with hairlines.
If it is meant for screen, I would first test it on different screens. Is this problem only with a few screen, I would ignore it, if it is common, I would make the lines wider. Contrary to print where a mixture of several inks might become problematic or thin lines with screened rasterized single colors look bad, on screen it is not the case, so you could make these lines thicker but make them feel lighter with a brighter color. Maybe that the print version and the screen version of the PDF should have different graphics.
Thank you for your response. The textbook is to be printed and presented as an ebook. The print version is not a problem nor is the ebook version when viewed in a pdf viewer other than Adobe Reader, or in Adobe Reader in the non-default state with the Thin Line Enhancement feature disabled.
I attempted to resolve the Adobe Reader Thin Line Enhancement problem by increasing line widths and ensuring that interrupted lines segments were aligned. Sadly, the overall size of the illustrations limits the the maximum width of the thinnest lines and Thin Line Enhancement problem persisted.
The reason I ask if there is anything which can be done within InDesign to counter the distortion of Reader's Thin Line Enhancement is the following observation. An MS Word document with the same illustrations embedded as png graphics and saved as a pdf does not suffer the Thin Line Enhancement distortion when viewed in Adobe Reader. I am hoping that whatever is done when MS Word saves a document as a pdf can be replicated when InDesign exports a pdf. Unfortunately, I am constrained by my publisher to link rather than embed the graphics. I have experimented linking eps, Illustrator, and pdf graphics files but they pdfs exported from InDesign were distorted when viewed in the default configuration of Adobe Reader.
I must disagree with your assertion that the only correct way to view the pdf is in Adobe Reader. Adobe Reader distorts the images unless the user has disabled the Thin Line Enhancement. I believe that I am a typical user of Adobe Reader in that I was unaware that the feature existed until recently. I mistakenly presumed that what may have been distorted graphics were simply poor quality graphics. Given my choice, I would hope that none of the future readers of the text use Adobe Reader, but, unfortunately, I know that many will. That is why I am attempting to resolve this problem.
What format are the line drawings you placed in ID? I suspect they're vectors...
Yes, the artwork is all vector graphics drawn in Illustrator.
I'm fairly sure enhance thin lines in Acrobat only works with vectors...
… An MS Word document with the same illustrations embedded as png graphics and saved as a pdf does not suffer the Thin Line Enhancement distortion …
As you already found out: depicting the graphics in a pixel based format like PNG will not show the problem.
Of course, "Thin Line Enhancement" is for vector graphics only.
PNG is pure pixels.
So in this case it might be better using PNG or any other supported pixel based image format to show your graphics. For the print version using vector graphics is the preferred solution.
Now for the hard part:
How to convert the 1300 drawings to png files and place them in InDesign?
Answering this question right now is impossible, because we do not know how these vector graphics are placed in InDesign, what kind of file type is used for them or if they are not placed but made in InDesign entirely.
I'm not sure if that amount of work is worth the effort. Informing your readers about unticking "Enhance Thin Lines" in Adobe Reader's Page Display Preferences could be a better way.
Thank you for the explanation.
Thank you for your response.
I believe enhance thin lines only applies to lines (strokes), so I suggest you use Acrobat to convert all strokes to outlines. This won't change the width of the line, only the way the anchor points make the line. One way to do this in Acrobat is to go to Tools> Print Production> Flattener Preview> convert all strokes to outlines. I can't promise this won't change the appearance of some of the illustrations, but it might work for you.
It works! Thank you.
You're welcome. It occurred to me that your thin lines might be too small to print. I know some rips will enlarge hairlines, to ensure they image (but possibly not outlines), so you will want to keep a copy of your final PDF with and without outlines and discuss this issue with your printer. I would also recommend a press check, to insure your illustrations are appearing as you expect.
@SeelerK – I suggest you mark Luke's answer #9 as "Correct" …
@Luke – very good advice!
There are now two pdfs which differ by the file type of the linked figures. The print version was left unchanged with linked Illustrator files for the figures. The ebook version has linked pdfs with the strokes replaced by outlines per your recommendations.
Interestingly, the line drawings now have complete fidelity with the original Illustrator drawings when viewed in Adobe Reader with the Enhance Thin Lines feature enabled. The only lines which are now thickened randomly are some of the grid lines of plots. If I understand the history of the Enhance Thin Lines feature of Reader correctly, it is enabled by default to improve the appearance of spreadsheets. It seems as if something in the algorithm identifies grids, even when they are outlines, not strokes.
Again, thanks for your help.