Image aliasing when exporting print PDF at 300 ppi (bicubic downsampling)

Question

Hello,
i am trying to describe a problem which persists since version CS3 of InDesign. It's about aliased edges in images in a certain angle; occuring when exporting the brochure as PDF file (at 300 ppi). The placed images are always at a higher quality than needed (for example 780 ppi effective). The aliasing is not there when opening the original image files in photoshop (viewing at 100%).
The PDF export settings are:
- Compression: Bicubic downsampling to300 ppi for images above 350 ppi (for color images, grayscale images and monochrome images)
- Crop Image data to frames
- Marks: Crop Marks and Page Information
- Output: No Color Conversion
- Advanced: Transparency Flattener: High Resolution
- Compatibility: Acrobat 4 (PDF 1.3)
- PDF /X-3:2002
Below are two screenshots
- The left one was the original image, downsampled to 216 mm in width using automatic bicubic downsampling
- The right one is the result when exporting a InDesign Document with the same width to a PDF with the mentioned settings
Downsampled in Photoshop CS6 to 216 mm width
Exported from InDesign CS6 with mentioned settings
I have no clue what happens here, but it looks like the internal downsampling of InDesign CS6 is not very good.
When i write a PostScript file of the brochure and put it in Distiller (with the same PDF Preset as above), the image looks like the one made with Photoshop. So this problem has to lie somwhere deep in InDesign or it's settings.
Anybody with similar experiences?

Answer 1

Rob Day wrote:
Something about your test looks off. The export from ID and export from PS PDFs are both zoomed at 1200%, but the export from ID vrsion is 90% smaller.
Yeah I noticed that I actually had the image in InDesign scaled @ 90%, so the effective ppi was around 650.  I get the same jagged results when I use anything other than a 300 or 600 effective ppi.  Whereas if I use a 650ppi image in Photoshop and export to PDF, it downsamples smoothly.
Rob Day wrote:
The diagonal lines in your test are 1 pixel so at 300ppi to an offset press at 150lpi, the lines would be less than a halftone dot so I'm pretty sure you would need a loupe to see any difference. Maybe with a stochastic screen there would be better resolution but still difficult to see. So if the printing is that good I would just export without down sampling. With disk space running at 15 cents a gigabyte there's not much to gain with a downsample.
It becomes noticeable with some images more than others, but I'm printing a lot of images of buildings and drawings with sharp lines that converge to a point, or are distinguishable in the full size image but indistinguishable when downsampled.  This can introduce distracting patterns when they aren't downsampled smoothly, something like this:
Unfortunately the printers near me aren't very good, so I'm having things printed online, and this particular printer (blurb.com - for a small job) won't accept large PDFs without compressed/downsampled images :/  I'm making 300dpi versions of the really crucial images for the time being, but I'm hoping there is a better solution!
The other issue is exporting the PDF for use on the web, either as a download or on an online PDF viewer like issuu.com.  The two PDFs on the right side of my test look much better in these situations.  Is there any disadvantage to using Distiller to make my PDFs for this purpose using the Device Independent setting?  I don't have any special interactive elements.