Best way to compress PDF without losing quality

[Zola John]

I constantly have to export PDFs to upload to website, so in the end, they need to be small but keep good quality. Often, I use the 'Reduce File Size' tool, but sometimes the quality gets too bad. 

When I'm using InDesign, I export PDFs in lower DPI (around 150dpi), but depending on the layout this action is not enough. 

Does anyone have better ideas of how to compress big files without losing quality? 

Cheers. 

[gary_sc]

Not seeing the pdfs in question, it's hard to k ow the best strategy but images are the primary problem/issue with file size. When you push compression too much, that's when quality goes down the tubes. 

Was this pdf from scanning or what?

[Zola John]

Mostly the PDF are menus that we upload to the company website. You can find one example attached.

Initially, it was 14MB and after reduced in Acrobat went down to 7MB. 

But it's still quite heavy for one page PDF which has only one image. 

[Bernd Alheit]

What happens when you use a image for the flowers?

[Test Screen Name]

I've analysed the file. You say it has only one image. But no, it has no images at all, and this is the key. Zoom in on the flowers in Acrobat. And zoom in again. And again. The detail is exquisite. This is an extraordinary vector drawing. Lovely, but nothing can be done to shrink it.  In controlling the size of a PDF, you need to control what goes into it. In the worst case (picture chosen by someone who cannot be overruled), you can rasterise the picture to an image.

Once you have an image you can compress it. Compressing images is exactly the same as reducing quality - that's what it means. You can only decide on your threshold of acceptable quality vs. size; or use less of them.

[Bernd Alheit]

Try the PDF Optimizer of Acrobat Pro.

[JR Boulay]

I cannot tell you why but the problem is here:

[Bernd Alheit]

The content streams comes from the flowers.

[JR Boulay]

PS : you should write "crémeux" not cremeux.

[gary_sc · Accepted solution]

Hi Zola,

I just had a chance to see your screenshot and can IMMEDIATELY see the issue: it's that dark gray background you have. Every pixel that makes up that background counts toward the total size of the document. If you were to use a white background, the size would go down exponentially. And going to a light gray would not make a difference: it's not the shade or hue, it's the fact that they exist.

On, in another way, if someone were to ask if they could use your printer to print this, and they wanted to print 100 copies, how fast would your ink supply hold up?

It's a beautiful design, if you want this to have a smaller storage size, come up with a beautiful design on white.

[JR Boulay · Accepted solution]

Now I can tell you why: the flower bouquet is not a pixel image, it's made of billions vectors, see it below when "Edited with Illustrator".

Pixels can be downsampled and compressed using a lossy format (JPEG).

Vectors can only be compressed without loss (ZIP) and therefore there is a low limit.

So, in InDesign you should replace this vector image by a pixel image before exporting to PDF.

[JR Boulay · Accepted solution]

And also, you should export the PDF in RGB mode, the file will be smaller and CMYK is useless on the web.

[Zola John]

Thank you all for the help! 

Cheers.