Can I ask InDesign to resample as it exports to PDF?

Question

When I export an InDesign CS document to PDF I'd like to know what InDesign does to the images that it exports. InDesign Help, in this case, was no help.
I'll give a preamble so you know what I'm on about. Originally when I first started this project 2 years ago, I thought I would layout the images within InDesign, and just before printing I would go through every one of the 800 or so images in the book (it's a big book), and crop and resample them to 300 dpi at exactly the final printed size. Big job.
After a few months of using InDesign I thought: no, I won't do that. When I export to PDF I'll assume InDesign will give me options to 'crop to frame size' and set the ppi to 300 dpi as well as converting images to grayscale if I so choose. It'll be automatic.
I'll make it clear with an example. Let's assume an original image was scanned to give an image that is 4000 pixels wide and 2000 high, and that the final image is 20" x 10". It is to be printed on a Xerox iGen which requires 300 dpi for no loss of quality. So how does InDesign get that particular image into the PDF?
Q1: Does it resample and export at 300 dpi? i.e. in the example above, will it export an image of 6000 x 3000 pixels to the PDF?
Q2. Or does it export the original image and does nothing to the image except cropping if I ask it to? If it needs resampling that will be done at print stage by the iGen.
Q3: I didn't see any options for converting to grayscale. Can you export a PDF as grayscale?
Why I am concerned about this is because if the original image is exported, that may cause me file-size problems. I scanned most of my images at 20MB-60MB, yet a lot of them when printed will be of the order of 20 square inches and only require about 6 MB for adequate printing. I may end up with a PDF file that is 5 to 10 times larger than necessary.
The real problem I have is: I trust PS and InDesign to resample my images, but I don't have that kind of faith in the iGen. If I can't ask InDesign to resample images when it exports, I may have a problem.
When I did my original series of test prints in July 2006 on the iGen, I cropped and resampled the images ready for printing before I imported them into InDesign. So I haven't tested the iGen's resampling capabilities. I be blunt I don't trust it. The iGen ( a machine costing in the millions) failed a simple test of converting colour documents to grayscale. Here are my notes written at the time:
b Converting to Grayscale using the iGen
Do not use the iGen RIP to convert colour images to grayscale because it converts all gray densities above 90% to 100%. ie dark shadows end up as 100% solid black shadows with the accompanying sheen. I measured this figure from the K-only gradient at the bottom of the page. It appeared solid black for the first 9mm of a 96 mm black-to-white gradient. All densities between 100% and 91% ended up as 100%. The effect is very obvious in Mums hair which became a solid mass.
My full notes on the iGen are here: http://jucreek.googlepages.com/temporary if anyone wants to have a look.
Anyway, that's why I have concerns about images. Maybe I should just knuckle down for a week and go through 800 images, cropping and resampling every one in Photoshop. Talk me out of it, please.
And that brings me to my final question:
Q4: Can I ask InDesign to do that job for me: to crop, to resample at a certain dpi, and to overwrite the original image so that it all matches up?

Answer 1

Guy,
Let me try to recap all your statments with my comments:
> Let's assume an original image was scanned to give an image that is 4000 pixels wide and 2000 high, and that the final image is 20" x 10". It is to be printed on a Xerox iGen which requires 300 dpi for no loss of quality.
From the very start you're in trouble.
The image size you describe, set at 300 dpi, will only be 13 1/3" by 6 2/3". If the image is scaled up to be 20" by 10", it will only be 200
>dpi.
So, we're starting with insufficient data according to your requirements.
Nothing that InDesign or Acrobat does can make that image the correct resolution.
> Q1: Does it resample and export at 300 dpi? i.e. in the example above, will it export an image of 6000 x 3000 pixels to the PDF?
No, InDesign and Acrobat's print device will only resample
b down.
Neither will resample up.
> Q2. Or does it export the original image and does nothing to the image except cropping if I ask it to?
The image created in the PDF will be cropped. It doesn't touch the original file.
> If it needs resampling that will be done at print stage by the iGen.
I believe the iGen will only resample
b down
the same as InDesign and Acrobat's creation of the PDF.
> Q3: I didn't see any options for converting to grayscale. Can you export a PDF as grayscale?
As mentioned, that won't happen in the PDF Export but will happen with the PDF Print driver. However, that will also convert colors in the ID file, not just images, to grayscale.
> Why I am concerned about this is because if the original image is exported, that may cause me file-size problems. I scanned most of my images at 20MB-60MB, yet a lot of them when printed will be of the order of 20 square inches and only require about 6 MB for adequate printing. I may end up with a PDF file that is 5 to 10 times larger than necessary.
Perhaps I did my math incorrectly, but in your original example, 4000 x 2000 pixels cannot be set at 20 inches by 10 inches at 300 dpi.
It requires 6000 by 3000 inches to be 300 dpi at 20 inches by 10 inches.
> The real problem I have is: I trust PS and InDesign to resample my images, but I don't have that kind of faith in the iGen.
I don't think you need to worry about the iGen if you set your images correctly. But as I said above, you haven't sampled them enough. So the iGen isn't going to do anything.
> If I can't ask InDesign to resample images when it exports, I may have a problem.
You set ID and Acrobat to
b downsample
not
b upsample.
> When I did my original series of test prints in July 2006 on the iGen, I cropped and resampled the images ready for printing before I imported them into InDesign.
Cropping and resampling in Photoshop is always preferred as you have the options for how the resampling occurs that neither ID nor Acrobat have.
> So I haven't tested the iGen's resampling capabilities. I be blunt I don't trust it. The iGen ( a machine costing in the millions) failed a simple test of converting colour documents to grayscale.
No, I wouldn't have expected the iGen to convert to grayscale at all! Converting to grayscale can be done in the Acrobat print driver, but I would prefer to do it in Photoshop if I demanded very refined conversions.
> My full notes on the iGen are here: http://jucreek.googlepages.com/temporary if anyone wants to have a look.
See my comments above.
> Anyway, that's why I have concerns about images. Maybe I should just knuckle down for a week and go through 800 images, cropping and resampling every one in Photoshop. Talk me out of it, please.
You can resample using Photoshop's batch processing, but depending on the type of cropping that might need to be done manually in Photoshop. But if the cropping is always of a certain size and position that could be done in batch processing.
> Q4: Can I ask InDesign to do that job for me: to crop, to resample at a certain dpi, and to overwrite the original image so that it all matches up?
No, InDesign doesn't overwrite your original image, but it will change the image in the final PDF.