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Yes Photoshop does not seem to change image size resolution correctly. For some reason it converted 300DPI set in the Image size dialog to 118.11 Pixels/centimeter when ruler units are inches?? Go figure out the on 118.11Pixels/centimeter is 299.999DPI.
The document I created in the new document dialog was 30CMcx20CM resolution 100pixel/centimeter
The event change that document to 10" x 6.667" so ruler units was changed to
30cm at100px/cm=3000px and 3000/300dpi = 10" so CM to Inches seem to go well the action step recorder was Image size resolution 300 per inch why did Photoshop convert that to 188.11 Pixel/centimeter?
Here is the ExifTool command (Mac OS). Simply change the path at the end to the target top level parent folder on your system. ExifTool is a command line program, so you will need to use Terminal.app on the Mac or the Command Prompt in Windows. There are 364 characters in the code below, if you copy/paste ensure that quote marks do not become curly. The last 45 characters in orange need to be removed and replaced with a valid file path on your OS. On both Windows and Mac you can drag n drop a folder or file in the GUI into the command window to populate the path (then you don’t need to worry about the quote marks). Finally, press return to process the command.
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exiftool -IFD0:XResolution=300 -IFD0:YResolution=300 -IFD0:ResolutionUnit=inches -Photoshop:XResolution=300 -Photoshop:YResolution=300 -Photoshop:DisplayedUnitsX=inches -Photoshop:DisplayedUnitsY=inches -XMP-tiff:XResolution=300 -XMP-tiff:YResolution=300 -XMP-tiff:ResolutionUnit=inches -r -overwrite_original_in_place '/Users/currentuser/Desktop/top level folder'
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For Windows OS, simply change the straight single quote marks to straight double quote marks and provide a valid path replacing the last 45 characters in orange.
Work on duplicate files until you are sure that there are no problems. In my tests, JPG/PNG/TIF/PSD were processed with no problems. I did have some issues with raster DSC EPS files, so I would avoid processing them, not sure about other file formats. One can also ignore specific folders and only process specific file types. This command will overwrite original files, so work on copies or have backups and test that files can open or be used without issue. This would process all sub-folders within the main top level folder.
I do not know why Photoshop seems to default to showing resolution in the image size dialog covered to pixels per centimeter.
Photoshop is not a file editor and all Photoshop documents are not opened using a file. There is no file backing a new Photoshop Document. There is no file for new documents.
With Photoshop you can display the document size with any units you want in image frame windows the image's Rulers units. In the Image Size dialog any units you want to show.
The event action change the documents resolution to 300DPI however the Image size Dialog defaults to displaying Resolution as Pixels per centimeter. I do not know why Photoshop does this. The Document I showed had no file. It was opened as a new document 30cm x 20 cm at 100 px/cm. If you do the math that is 11.81" x 7.87" at 254px/in. The action changed the resolution to 300px/in the document became 10" wide. The event action worked perfectly.
Photoshop is a Pixels editor it works on Pixels and with a resolution in dpi px/inch. Here is a script like the action however it will spell out the documents resolution. The script puts out a script alert about the document resolution. Then the Script the resizes the document to the same number of pixels wide and the same number of pixel high and set the resolution to 300. The script then puts out the document current resolution the script deals with Pixels like Photoshop no other the units. It does set Photoshop ruler units to inches to have Photoshop to display document size information in inches as the scripts ends execution. During the scripts execution you can see how the image windows ruler units changes. Sill Photoshop defaults to showing Image resolution in the image size dialog as px/cm, shows the width and height in Inches like ruler units are set. The script change to resolution to 300 DPI like the Action did and even put out and alert to show the current resolution is 300. You can see that the document width change from 11.81" to 10" the document width and height are being display in inches the resolution is 300DPI but Photoshop displays resolution as px/cm not px/in
app.preferences.rulerUnits = Units.PIXELS;
alert("Resolution=" + app.activeDocument.resolution);
//app.activeDocument.resizeImage(app.activeDocument.width,app.activeDocument.height,300);
app.activeDocument.resizeImage(app.activeDocument.width.value,app.activeDocument.height.value,300);
alert("Resolution=" + app.activeDocument.resolution);
app.preferences.rulerUnits = Units.INCHES;
Q: Is there a way to make photoshop default open an image as ppi?
Yes, a script or action can be set to change the opened image’s resolution unit value to PPI, this can then be automated to be applied on every image opened into Photoshop using the File menu > Scripts > Scripts Events Manager.
The following image uses a different script and is simply used to illustrate:
Q: Is there a action you could suggest that would fix this?
If other software is marking the images in CM rather than IN, then you will need to fix it at the source, otherwise the Script Events Manager would hopefully fix the issue on open, save, or export.
Q: Is there a way Bridge CC could open the file in ppi, much the same as Lightroom in its preferences?
Bridge is a file browser, it will show the metadata value in the file. It appears that Bridge shows the value as PPI, even if the file is saved as PPCM.
Another option would be to use ExifTool to batch process folders/images, changing the unit value from CM to IN:
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