With the JPG versions you will loose transparency.
If you have the very same color settings in Photoshop and in InDesign you will get the very same results in both applications.
Do you all agree?
If the quality setting was too low when the .jpg files were saved then you might see artifacts.
Also, your InDesign Color Settings' CM policies when the ID file was created would affect the color conversions when you export. So for example if you started with an RGB image with AdobeRGB embedded, duplicated it, converted to US SWOP Coated, placed both in an ID layout with Color Management Policies set to Preserve Embedded, and the assigned CMYK and RGB profiles as US SWOP Coated and AdobeRGB; you would get a match if the Destination profile was US SWOP and the ID Rendering Intent and Black Point Compensation settings matched your Photoshop settings.
There are lots of ways you might not get a match. If you did the same as above, but with the CMYK CM Policy set to Preserve Numbers (Ignore Linked Profiles) and US Sheetfed Uncoated as the InDesign assigned profile and destination, you would not get a match.
If your question is—given the same color settings is the conversion from RGB to CMYK the same in Photoshop or ID export the same? Yes.
Thanks for good answer.
I've made a test where I imported this four file format to a inDesign document and got a proofing from it. It is not possible to see any difference in the picture from this different file formats. It also looks the same in the exported PDF file on the screen.
But as the pre print is a digital print, is there any risk that it might look different in a offset print?
If I use Adobe Acrobat Pro to open the image file from the PDF in Photoshop, it open with the extension .pdf - what file format is actually that file in?
In what format is the image file when it is imbedded in the PDF?
An image in a PDF is in PDF image format. It doesn't store image files, it is converted to PDF format, and then one of a number of compressions are done. Some compressions (e.g. JPEG, JPEG 2000) are lossy, others (e.g. FLATE/ZIP) are not.
The other crucial aspect is whether a profile is embedded and whether it is used.
PDF is one of Photoshop's native formats, could also have the extension PDP.
It is not possible to see any difference in the picture from this different file formats.
That's what you would expect if you synchronized both program's Color Settings before you created the files. Keep in mind that syncing is only useful for future documents, existing document's can have their own embedded profiles and CM policies that might be different than either program's current Color Settings'.
If the question is does Photoshop make a better conversion to CMYK than InDesign? Then no, unless you need to make a CMYK edit like setting black only type or forcing an out-of-gamut-to-RGB color like 100% cyan.
Also if you are going to make conversions at output or export you might consider the affect of the rendering intent on different kinds of images, which can have a very big affect on how colors are brought into the CMYK gamut. InDesign lets you set the intent on a global or individual image basis.
Thanks! Your answers is to good help.
There is one other thing i'm thinking of.
Most often the effective PPI will become less than the image actually PPI. On my digital test print I have one image with 218 PPI and it look good. How low can I go in effective PPI before it get visible in the print? I understand that the limit is not absolute, but what do you normally allow?
Is there any difference in digital print and offset?
"Most often the effective PPI will become less than the image actually PPI. " Why do you say that?
I guess it's just because I have a tendency to draw the image a little more than I expected when exported them from Lightroom. I need to change that...
But what would you say is the lowest to go with the effective PPI for high quality offset print?
It depends on the nature of the image. Line drawings, and images with sharp edges (for instance architectural or automotive images) will suffer more than softer images. It also depends on the screening method and frequency, and the viewing distance. If you really want a figure, I'll say 200ppi, but the more experience you have, the more you develop a sense of what you can 'get away with'.
And I'd personally recommend RGB PSD for most images. This gives you the benefit of layers, lets you convert to CMYK downstream for specific printing conditions (you might want to use the same image in a newspaper ad and a large format inkjet poster, which would require very different CMYK values), and avoids the loss of quality (discernible or not) you get from JPEG compression.
Another way to look at it is as a relation to line screen (lpi). Do you know the line screen that will be used? "High quality" is a very broad category.
...what would you say is the lowest to go with the effective PPI for high quality offset print?
You can't just sidestep the technical nuances of image resolution as it relates to printed output, and arrive at a one-size-fits-all solution. There are too many variables; some of which have already been mentioned in other responses.