Actual ppi in indesign different from ppi in photoshop

[Parvathi24881399xiqs]

Hello,

I'm struggling to understand what is happening here. I have an image that I got from the client. When I open it on photoshop, it tells me it's a 300 ppi resolution picture. When I place the same image for layout in InDesign, it says actual ppi 180 in the links panel. Why is this happening?

Any explanation would be greatly appreciated. Thank you in advance.

[Parvathi24881399xiqs]

I had no idea that camera raw automatically converts everything to 300 ppi no matter the original resolution. Thank you  so much once again! 

[rob day]

The files i place in indesign are jpegs or tiffs only. Not raw files.

Then there is no reason to use Camera RAW to open the files.

[Parvathi24881399xiqs]

Yes, you are right. I'd turned that on to try the new AI enhance photo feature a while ago and never turned it off after that. I did not think that it would affect the images I didn't apply the enahance option to. That's where i went wrong. I've turned it all off now. Thank you.

[rayek.elfin]

Just a side note: never solely rely on the PPI parameter that is embedded in an image file. A 1px by 1px image file can be saved as a 300PPI image or a 100000px by 100000px image as a 1PPI one.

So always check the actual pixel resolution and rely on that to prevent nasty surprises. In particular when dealing with RAW and other images taken by a camera.

[James Gifford—NitroPress]

The PPI value encoded in an image file is an utterly arbitrary value meant to be of  "convenience" for users. It has absolutely zero effect on the image or file or anything else. Which is why usages like "a 300ppi file" make me grit my teeth. Ain't no setch animal.

BUT if you expect an app to read that value and place the image as a factor of pixel size / encoded PPI, and, as in this thread, it doesn't, something is wrong somewhere.

[rayek.elfin]

...which is why I am wondering about the actual pixel dimensions of the OP's image - and whether it changed throughout their workflow. That piece of information seems to be missing, because as you @James Gifford—NitroPress state, PPI is utterly arbritrary for anything else but placing it within a certain context (like print).

It seems weird to me that between Camera Raw and PS/other apps the PPI changes without a change in pixel resolution. Which is why it is important to not only examine the PPI value, but also the pixel resolution.

[rob day]

t seems weird to me that between Camera Raw and PS/other apps the PPI changes without a change in pixel resolution.

I think @Parvathi24881399xiqs  was opening a JPEG via Camera RAW from Bridge. If I do the same my Camera Raw Preferences determine not only the resolution, but the bit depth, and color profile.

For example, I can right click a JPEG in Bridge and ask it to be opened via Camera RAW. In that case my Camera RAW preferences affect the image processing even though this is not a RAW file—I have ProPhotoRGB, 16 bits, at 400ppi set:

When I click the RAW dialog Open button, the image gets processed into Photoshop at those specs:

But, if I open the same JPEG via Photoshop’s Open dialog, the original image opens at the original specs—8"x8.428, 182.25 PPI, 8-bit, with AdobeRGB assigned:

If I place the original, InDesign accurately reports the Actual Res as 182 with AdobeRGB embedded. The version opened via Camera RAW forces me to save when I try to close. If I do save and place, InDesign again accurately reports the Actual Res as 400ppi.

All images have a pixel dimension, but they also have a defined output dimension. The original in this case has a pixel dimension of 1458 x 1536 and an output dimension of 8" x 8.42", so the Actual PPI resolution is 1458/8 or 182.25PPI

[Parvathi24881399xiqs]

This is exactly what's happening to me. The same thing happens to Camera Raw of PS also not only Bridge. 

As you can see, it seems to be mandatory to put in a ppi in camera raw. Since I work with Books, the printers usually ask for all images to be at 300 ppi. So I didn't know this when i posted here, that camera raw assigns its own ppi to even jpegs. So now I'm opening it all on camera raw, making the images 300 ppi, editing them and then placing into indesign. (because the images supplied by the client, though high in pixel dimension, seem to only be 180ppi in the size of the book I'm making). (Just for clarification, the book I'm making only has full page bleed images - that's why I said the size of the book).

[Parvathi24881399xiqs]

I understand that the ppi by itself doesn't mean anything. But since I'm making a printed book, the printer needs all images to be in 300 ppi. 

[James Gifford—NitroPress]

Keep in mind that for print, everything is, or can be, managed in the export to PDF. As long as there is sufficient resolution in the original image files for Acrobat to include or downsample at 300ppi for a defined print resolution (DPI), nothing much in the source/ID file matters.

[rob day]

I understand that the ppi by itself doesn't mean anything.

In the Adobe apps PPI does have meaning—all Photoshop images have an output dimension (Width and Height) as well as a pixel dimension. The Pixels Per Inch number is the pixel dimension divided by the scaled output inch dimensions.

You can set the PPI of an image to 300 without changing its pixel dimenions (no Resample), but that changes the output dimensions. That’s what Camera RAW is doing—it’s not resampling the image.

When you place the 300PPI image in InDesign and scale the image, the pixels scale with the image—the scaled image no longer has an output resolution of 300ppi because its output dimensions have changed. That’s why the InDesign lists an Effective PPI, which in the end matters more than the Actual PPI.