Photoshop - verifying true resolution - how to find out if file has been resampled

New Here ,
Jun 06, 2021 Jun 06, 2021

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Hey all,

 

If you have a PSD file that should have been created in 300 dpi for printing but was only created in 100 dpi the print will be pixelated. If the image size is changed to match 300 dpi with resample ticked then the resolution does not change, only the physical file size. 

 

My question is this. If you recived said file above photoshop would display the resolution as 300 dpi but the true resolution is 100 dpi. Is there a way to find out the true resolution of a file you have been given without doing a physical print test? i.e. can you tell if someone has resampled or actually created the file with the correct 300 resolution from inception.

 

Thanks.

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Adobe Community Professional ,
Jun 06, 2021 Jun 06, 2021

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The true resolution is the number of pixels.

 

The ppi number is just metadata, it's unimportant in itself. You can change that arbitrarily without changing the actual data.

 

Resampling the pixel data will always cause severe quality loss. That's how you can tell.

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Adobe Community Professional ,
Jun 06, 2021 Jun 06, 2021

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Resampling the pixel data will always cause severe quality loss. That's how you can tell.


Without access to the source data it may be hard or impossible to determine if an image has been resampled, though, or if it is just blurry or otherwise sub-optimal. 

 


My question is this. If you recived said file above photoshop would display the resolution as 300 dpi but the true resolution is 100 dpi.

What do you mean? The effective resolution that is determined by the scale at which an image is being used in a layout application? 

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New Here ,
Jun 07, 2021 Jun 07, 2021

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Yes I'm refering to number of pixels. Sounds like it might not be possible to check this via a tool and you can only go by the naked eye. The problem is you can't really tell on a screen so I'll need to print it which takes time and $$. 

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Adobe Community Professional ,
Jun 07, 2021 Jun 07, 2021

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Unless you are creating photographic prints I think you may be looking in the wrong place; if an image is being used in a layout it matters little what its original resolution is – its effective resolution is what counts. 

And that can only be determined if one knows its final output size as set in Indesign or whatever application is being used to create the final output. 

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Adobe Community Professional ,
Jun 06, 2021 Jun 06, 2021

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You are mentioning resolution and print size without any mention of pixels that are most important when working in Photoshop. What matters most is number of pixels not resolution pixel per inch.

 

It seems you are looling at print size in cm or inches when ticking Resample and changing resolution pixel per inch. What you do not see is change in number of pixels in background. That is most important because if Ps does not have pixels it must construct them from nothing, just by looking at image and it must do that in seconds. ALgorythms are better and better but... Image will look blurry when upsampled as alreday stated above. 

"If the image size is changed to match 300 dpi with resample ticked then the resolution does not change, only the physical file size."

 

Maybe I do not understand well what are you talking about but still... The most important thing is how many pixels are there. I do not think you can track changes in file dimensions using metadata that ships with PSD file although I actually never though about that.

 

If you want to track such changes then you may be able using Preferences > History Log to Metadata. Edit Log Items > Detailed should work. Ask creator or sender of files to check that option before start to working on file.

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Adobe Community Professional ,
Jun 07, 2021 Jun 07, 2021

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While it is true that resampling will introduce artifacts what really matters is the final image. So, I would approach this differently. On receiving such an image, rather than worrying about the file history, whether it was resampled up or down, just look at the image. Either the quality will be good for printing or it will not. I've seen more images that I would reject for other reasons, focus - exposure - noise - camera shake etc than I would for resampling.

Dave

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Adobe Community Professional ,
Jun 07, 2021 Jun 07, 2021

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There are some photographic exhibitions and salons that demand the original file, and some that only allow a limited amount of cropping.  (Usually Natural History — Nature — categories).  If the psd file has photographic content, then you'd know the sensor size of the camera used to take it, but obviously not how much that content had been cropped.

 

The bootom line here is that with the quality of current lenses and cameras, you'd expect a certain degree of quality, and that would either be present, or it wouldn't.  Or you could take a really sharp image of your own, and up-res and up-res it again, inspecting the quality loss each time, and use that as a datum to judge said psd file.  You also need to take into acount the new Super Resolution feature in Camera RAW.

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