Downsampling only occurs on images above the threshold specified, so if your .png files are already low res they wouldn't get downsampled. There's only one compression setting availble, though, for all the images, though I believe that the Automatic setting varies the type of compression based on the image type.
well, maybe I didn't explain my intent clearly. I want to downsample some images alot (a background image for a full page, for example) and some images I want to leave at a high resolution (for example an image containing a logo or text). I'd like to do this all in ID. It seems like this would be a common thing to do.
1 person found this helpful
Well, I didn't find any way to do this in ID, but I do believe its a useful thing to do. In Fact, by doing some careful image-dependent compression, I was able to reduce the size of my pdf by half and have the result still look better than a standard uniform compression. What I did was:
first place all the images in the ID file, size and position them as they should be
then, looking at the rulers, note the horizontal size, in inches, of each image in the document
begin with the first image, open it in photoshop. If you want this image at 200dpi, for example, multiply the horizontal size (from ID) by 200. Change the image size in photoshop to this number.
save the image in photoshop as a jpg and compress as appropriate for the image type
go back to ID, open up the links window, select the image you just changed, and click the update link button
do this with all your images
when you go to export a pdf, don't do any compression or downsampling on the images.. they're already optimised
So as you can see you have to have some idea of the ideal target DPI and compression of each image in your document, and it may require some experimenting. But if you know that some images can be lowered much more than others, I recommend this method. As I said, in my case I was able to reduce the file size by half without negatively effecting the pdf appearance.
Is this for print or screen? I'm beginning to think the latter, and you want to reduce the file size by giving up quality selectively.
You seem to have worked out how to do it.
Replacing images in Acrobat (I'm on CC) was easier than I expected. While I wouldn't want to do this for every publication, I was able to copy specific graphics from one higher-res PDF and paste them into another, and it was pretty straightforward. Alignment is more fiddly than in InDesign, but this is so far the approach that works.
Would *love* to see image-specific compression settings somehow added to InDesign's export PDF feature, but (in addition to the backend technical complications) it might be a hassle even from the user perspective in general. More complexity...
Of course I could go and pre-downsample each image to the right size in photoshop, but that can get kind of involved.
That would not work anyway because ID takes the incoming pixels and recompresses them to the quality you choose on export. If compressed to a low quality in PS and exported to a high quality from ID you would get a low quality image without the compression.
Why do you want to do this? Are you trying to save disk space?
This is where 3rd party tools such as Enfocus PitStop Pro (a plug-in for Acrobat Pro) come into play.
Rob, I am guessing that there is content that ideally should be vector, however it is raster. So “logos” would ideally have a higher resolution than contone image content in this scenario to work around the quality issue.
Not necessarily. In my case, I was producing artwork in Illustrator that had complex brush strokes added in multiple places to give it texture. Using the vector artwork would have increased the final file size considerably, compared to raster. But I wanted this texture to come through in the final PDF, while still keeping nearby photos at a lower resolution.
So “logos” would ideally have a higher resolution than contone image content in this scenario to work around the quality issue.
I was referring to the compression setting not the downsample setting. If you place a lossy format like JPEG the compression artifacts are baked into the image, so when you export the image is recompressed and you would see little if any file size benefit by placing JPEGS.
With disk space running at 4 cents a gigabyte it's hard to believe a granular approach to image resolution and compression is worth the effort.
if this is all for PDFs that should be lightweight for web downloads and not for printing jobs one could do the following:
1. Export PDFs with different downsample settings
2. Merge the PDFs stacked with Acrobat Pro
Using the Layers functionality:
A. Import as Layer
B. Flatten Layers
To get the individual resolutions for individual images, set the images you do not want to see with a distinct export to non-printing.
If that idea will work or not work is depending on the structure of your layout. And it could be automated a bit by scripting. The extent of automation can be low or high. If the images that should not be downsampled can be identified by certain rules, naming schemes perhaps or other means like applied object styles of the used container frames etc. pp., it could be high. And also the individual exports can be done by scripting.