Is JPEG QuickProof same quality as JPEG 72 dpi?

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2 comments

  • Ian Wilson

    JPEG QuickProof generates output by reference to the preview only, without needing access to the original raw file. You can change the resolution of the QuickProof output to 72 px/in, 300 px/in, or whatever just as you can with the other recipes. What you can't do is change the % quality slider.

    The quality of the output for other JPEG recipes is determined by the Quality slider. The resolution slider makes no difference to anything except the size that the image will be printed at. So at 300 px/in, an image that is 6000x4000 px can be printed 20 inches wide by a printer using a 300 dpi resolution (6000÷300). At 72 px/in, the same image would come out almost 7 feet wide. (6000÷72 = 83.33 inches) For online use (for instance on a website) the image will come out the same whatever the resolution is set to.

    Whether the quality from JPEG QuickProof is adequate rather depends on what you are using it for. Probably fine for a small online photo on a website, but not ideal for printing from. 

    Ian

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  • Marco Hyman

    To expand on Ian's post...

    In the specific case of the QuickProof you do not have the option of changing the output size.   You are going to get the number of available pixels regardless of the value of the Resolution field.  You can prove this to yourself by using that recipe to output the same image twice, once at 300 and again at some other value.

    Both output files will be the same size.  Both will have the same dimensions in terms of number of pixels.  If you use something like exiftool to list the metadata and look at the differences you see exactly what changed.  Example:

    @@ -1,10 +1,10 @@
     ExifTool Version Number         : 12.00
    -File Name                       : 116Q5758.jpg
    +File Name                       : 116Q5758-72.jpg
     Directory                       : /Users/marc/Pictures
     File Size                       : 13 MB
    -File Modification Date/Time     : 2021:02:26 11:26:08-08:00
    +File Modification Date/Time     : 2021:02:26 11:26:41-08:00
     File Access Date/Time           : 2021:02:26 11:29:58-08:00
    -File Inode Change Date/Time     : 2021:02:26 11:26:08-08:00
    +File Inode Change Date/Time     : 2021:02:26 11:26:41-08:00
     File Permissions                : rw-r--r--
     File Type                       : JPEG
     File Type Extension             : jpg
    @@ -13,8 +13,8 @@
     Exif Byte Order                 : Little-endian (Intel, II)
     Make                            : LEICA CAMERA AG
     Camera Model Name               : LEICA Q (Typ 116)
    -X Resolution                    : 300
    -Y Resolution                    : 300
    +X Resolution                    : 72
    +Y Resolution                    : 72
     Resolution Unit                 : inches
     Software                        : Capture One 21 Macintosh
     Exposure Time                   : 1/1000

    The lines starting with - are from the image processed with the resolution set to 300 and the list starting with + are from the image processed with the resolution set to 72.   There are no other differences in the file.  Both image files are 3.6 MB in size.

    In other process recipes Changing the resolution may effect the processed file.   Another example:

    Image processed at 300dpi with the Scale set to Width and the size set to "5 in" results in a 1500x931 pixel image.  Changing the Resolution to 72 but leaving the Scale and size the same results in a 360x223 pixel image. 

    Changing the Resolution to generate more or less pixels is usually the wrong thing to do, IMHO.  I would only do it if preparing files for a publisher who specifically asks for an image of a specific number of in/mm/cm at a specific DPI.   When not using "fixed" I specify image sizes by number of pixels.   When using fixed or number of pixels the Resolution field is ignored.

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