PNG with transparent background is making my exported pdf huge

[katielady1]

Hi there, 

I have a multipage document with a ton of images saved as pngs with transparent background. However, when I export a pdf from InDesign using the (smallest file size setttings, the file is massive, 20 MB). I exported each page individually so I could sort out where the issue is, and have narrowed it down to two pages. Each have a transparent png on them (that is about 9MB). I have tried saving the png as tiff or psd files (even tried unchecking maxium compatibility) and those files leave me with images are are even larger than the png, but the exported png is still huge. I have comparably sizes transparent pngs on many pages but just these two are causing problems. Thanks, advance. 

[katielady1]

Like one single page exported is 9MB and the other is 5.3MB and thats on the smallest file size setting. 

[James Gifford—NitroPress]

The exported file size is going to depend on the actual pixel size of the image in the document and the export resolution. The document image-file size is the less important one, since export resamples it to a (usually) smaller size.

That is, you can use a huge image file in an ID doc, but if it exports at 2x3 inches at a 300ppi export resolution, it's not going to add much to the PDF size.

On the other hand, if your images are pages size (say 6 x 9 inches), export at 300ppi will mean an image embedded in the PDF that's 1800x2700 pixels. That's going to be a large image, and bulk out the PDF, pretty much no matter what you do.

Transparency is an issue, too, but not quite as absolute a one. If you're flattening transparency, it won't add much to the file size. If you're not flattening transparency, it can add quite a bit, for a variety of technical reasons.

But mostly, if you have large page images, you're going to have large PDF files. The solution is to replace the image graphics with vector graphics, if you can.

[katielady1]

Thanks for your reply, James. I've included a few screeshots of info here. An example of an image that causes a huge file to be produced. And one that does not. Both transparent PNGS.

Image 1 (file name starts with PXL)

Used on a page that when I export at the smallest file size preset in indesign creates a page which is 9 MB

Image is 7.2in x 5.4in on a 8.5 in x 11in page.

See other details in screenshot.

Image 2 (file name starts with 522...this one does NOT create a huge pdf file)

Used on a page that when I export at the smallest file size preset in indesign creates a page which is 162KB

Image in placement is 7.2in x 7.9 in on the 8.5 x 11 page

See other details in screenshot.

I don't get why one is causing huge problems, and the other is not (and I have tested all the elements on the pages, it just comes down to the images). 

[katielady1]

Okay. Here is an updated. I took the pngs that were causing problem and copied and pasted them into a new PSD file but changed the colour profile to Adobe RGB and resaved it. Now the page exports to 106KB. Down from 9MB.

I did try just changing the profile within the original document, but it didn't reduce change the end result. But setting up a new document with the different profile, then copying and pasting and resaving made the difference. 

[James Gifford—NitroPress]

It sounds as if you're on the right track, but copy and paste is not often the best way to reformat images. (I would have opened the PNGs and resaved as PSDs, for example.) It also sounds as if you might have had CMYK files, which are much, much larger than most RGB profiles.

As long as you are getting the final document resolution you want, though, it sounds like you solved the size problem. In the future, keep in mind that PSD is a superior format for complex images (with transparency, etc.) within InDesign. There are several levels of interactive control with PSD that make it easy to adjust the final result.

[katielady1]

Hi James. The orignal files were RGB, not CMYK. But yes, I also copy and pasted into a new PSD document with the same results (small files size on export). 

[rob day · Accepted solution]

pasted them into a new PSD file but changed the colour profile to Adobe RGB and resaved it. Now the page exports to 106KB. Down from 9MB.

Hi @katielady1 , It’s more likely a ancestor metadata problem, which you fixed by pasting the pixels into a new doc. A color profile would only be around 100K.

More on the metadata bug here:

https://community.adobe.com/t5/indesign-discussions/file-size-is-too-big/td-p/9370587#10084949

[katielady1]

Ah, that makes sense! I just was racking my brain on why these two files where causing me problems. 

[Willi Adelberger]

Where do the PNGs come from?

1. If they are from Illustrator, use AI files.
2. If they come from Photoshop try PSD, PDP or PDF.