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I'm having issues rasterizing images for inclusion in PDFs. I currently rasterize in Illustrator, import to InDesign, and downsample from roughly 300 ppi to 150 ppi, or thereabouts. I would prefer to rasterize to 150 ppi in InDesign instead but that doesn't seem to be possible. The resulting images are always "crunchy" regardless of the Illustrator output resolution. I've tried going as high as 600 with PNGs. The images look okay coming out of Illustrator.

Also, when I then view these PDFs in Acrobat, there are often small image errors that only appear at certain zoom levels.

Images below:

Crunchy

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Error

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To the best of my knowledge, the errors are caused by exporting to the PDF/X-1a:2001 standard in InDesign. This standard splits some images into smaller components, an example of which is provided below. The other standards don't appear to do this.

enter image description here

The gray lines are the borders of the panels into which the image was split when exported. You can see this by clicking "Edit PDF" in Acrobat.

The crunchiness appears to be related to rasterization of a relatively low-resolution image. When first exported at 900 ppi instead of 300 ppi, the final, downsampled image (~150 ppi) is a far better approximation of the vector original. At the very least, the edges are better defined and there are fewer to no "steps" on straight lines. Some of the "crunchiness" that I saw earlier was actually related to exporting to PDF/X-1a:2001 and not to rasterization.

enter image description here

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  • "The other standards don't appear to do this" - is this the only one that removes transparency? – Jongware Dec 27 '16 at 20:13
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The "image errors" appearing at certain zoom levels are essentially rounding errors when Acrobat renders the document. This is pretty much normal behavior, but you can try playing with the display options in the Preferences, to see where you get the best (or least bad) results.

What kind of images are you rasterizing? vector images, raster images?

The former should better be kept as vectors as long as possible (in other words, keep them in the PDF). For the latter, there is a simple tool which can resize raster images much better… this tool is called … "Photoshop". But again, why not keep the initial resolution (with raster images) as long as you need, and let the PDF/Acrobat to its thing?

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  • I'm rasterizing vector images, almost always line work like above. This is for a portfolio that needs to meet size limits so I fine-tune the downsampling to control file size. I also export as PDF/X-1a. – Jason Dec 16 '16 at 18:35
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    With all due respect, but I would strongly suggest to revise the workflow. Rasterizing vector data for PDF output makes no sense at all (well, if your vector drawings are very complex, even after optimizing them, you will get better performance with rasterizing, but such drawings are very complex, such as a complete machine/vehicle, in isometric view, drawn with some specific software). And when it comes to create (just for printing) PDF/X-1a, Acrobat knows best what to do, and if you rasterize, you will (not even may) interfere with Acrobat's mechanism. – Max Wyss Dec 16 '16 at 18:53
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Place the unedited PDF in indesign sized as appropriate, export to PDF using a custom preset: under compression, set "downsample to 150ppi when image is above 150ppi" for both greyscale (256 greys) and color images, possibly also monochrome (aka one-bit color bitmaps).

This allows you to work with the original document(s), defers downsampling to output time, and allows for rapid creation of multiple quality versions.

If you are targeting monitors (rather than print) check the output section: consider converting the colors to destination and setting the destination to an RGB profile. Since CMYK has four channels instead of 3, each CMYK image has 25% more pixel data given the same dimensions in pixels.

Your samples look like they could be vector, but you might be experiencing quality issues if your originals are raster images. Low pixel density, one color, high contrast is the worst-case for highlighting aliasing artifacts in imagery.

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  • If the image in the unedited PDF is vector instead of raster, will InDesign convert that image to raster on export? i.e. Will a vector image in a PDF, when placed in InDesign, export as a raster? I have been rasterizing my vectors out of Illustrator because placing a vector image into InDesign appeared to leave the image as a vector on export. – Jason Dec 27 '16 at 20:13
  • vectors will export as vector, but you can try flattening 100% using pdf1.4 compatibility. Another trick is to place the pdf/vector, and then move it (i.e. break the Link). The Preview image will then be used. – Yorik Dec 27 '16 at 20:39

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