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I have images that I generate via ImageMagick that are supposed to have a non-square pixel ratio.

Photoshop seems to be able to detect that the pixel ratio is not square (I see that there is a custom pixel ratio set up) but I cannot tell where the ratio came from, as it is different from the resolution I set.

So the question is - where does Photoshop get the pixel ratio from?

This the output from identify:

 Image: strange.png
   Format: PNG (Portable Network Graphics)
   Mime type: image/png
   Class: DirectClass
   Geometry: 734x995+0+0
   Resolution: 23.63x36.52
   Print size: 31.0622x27.2453
   Units: PixelsPerCentimeter
   Type: TrueColor
   Endianess: Undefined
   Colorspace: sRGB
   Depth: 8-bit
   Channel depth:
     red: 8-bit
     green: 8-bit
     blue: 8-bit
   Channel statistics:
     Pixels: 730330
     Red:
       min: 25 (0.0980392)
       max: 255 (1)
       mean: 182.009 (0.71376)
       standard deviation: 87.5167 (0.343203)
       kurtosis: -1.61776
       skewness: -0.485718
       entropy: 0.342994
     Green:
       min: 38 (0.14902)
       max: 255 (1)
       mean: 188.828 (0.740503)
       standard deviation: 72.5125 (0.284363)
       kurtosis: -1.26545
       skewness: -0.481082
       entropy: 0.357498
     Blue:
       min: 0 (0)
       max: 255 (1)
       mean: 150.706 (0.591004)
       standard deviation: 110.202 (0.432163)
       kurtosis: -1.67965
       skewness: -0.294347
       entropy: 0.346663
   Image statistics:
     Overall:
       min: 0 (0)
       max: 255 (1)
       mean: 173.848 (0.681756)
       standard deviation: 91.3995 (0.35843)
       kurtosis: -1.14615
       skewness: -0.580943
       entropy: 0.349052
   Rendering intent: Perceptual
   Gamma: 0.45455
   Chromaticity:
     red primary: (0.64,0.33)
     green primary: (0.3,0.6)
     blue primary: (0.15,0.06)
     white point: (0.3127,0.329)
   Background color: white
   Border color: srgb(223,223,223)
   Matte color: grey74
   Transparent color: black
   Interlace: None
   Intensity: Undefined
   Compose: Over
   Page geometry: 1021x1103+218+58
   Origin geometry: +218+58
   Dispose: Undefined
   Iterations: 0
   Compression: Zip
   Orientation: Undefined
   Properties:
     date:create: 2016-01-26T09:42:53+01:00
     date:modify: 2016-01-26T09:42:53+01:00
     png:bKGD: chunk was found (see Background color, above)
     png:cHRM: chunk was found (see Chromaticity, above)
     png:gAMA: gamma=0.45454544 (See Gamma, above)
     png:IHDR.bit-depth-orig: 8
     png:IHDR.bit_depth: 8
     png:IHDR.color-type-orig: 2
     png:IHDR.color_type: 2 (Truecolor)
     png:IHDR.interlace_method: 0 (Not interlaced)
     png:IHDR.width,height: 734, 995
     png:oFFs: x_off=218, y_off=58
     png:pHYs: x_res=2363, y_res=3652, units=1
     png:sRGB: intent=0 (Perceptual Intent)
     png:text: 2 tEXt/zTXt/iTXt chunks were found
     png:tIME: 2016-01-26T09:42:53Z
     png:vpAg: width=1021, height=1103
     signature: 4be6c7cdfbf701380737943a2363a747c47da9281caba9fe053da6ca0e89b2e3
   Artifacts:
     filename: strange.png
     verbose: true
   Tainted: False
   Filesize: 114KB
   Number pixels: 730K
   Pixels per second: 365.17GB
   User time: 0.000u
   Elapsed time: 0:01.000
   Version: ImageMagick 6.9.2-10 Q16 x86_64 2016-01-21 

and the custom pixel ratio automatically set up in Photoshop is 1.533, although, given a resolution of 23.63x36.52, I should have something like 1.545, which is 36.52 / 23.63.

  • Look at Resolution. For a square pixel, the horizontal and vertical values would be equal. – usr2564301 Jan 26 '16 at 9:10
  • @Jongware - that doesn't seem to work. If I use the resolution I should get something else as the pixel ratio - namely 1.545, from Resolution: 23.63x36.52 – simone Jan 26 '16 at 9:17

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