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So I tried resizing. I have a photo scanned from a slide at 4000 dpi. I go to resize document. It says 16x20cm print size at 300dpi. I accept. Then I export to TIFF. The TIFF is still 4000 dpi. What is going on?

 

Best regards

Geir Rosset

Oslo

Norway

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Hi MEB!

 

I have the same issue with a .TIFF file that I am trying to resize from 72 to 300 dpi. I am unchecking Resample and trying to export the document with different name but nothing seems solve the issue. I noticed that if I save the file in .AFPHOTO and I open it again with Affinity the DPI has been changed but if I export it again in TIFF format the DPI come back to 72 DPI.

 

Can you try to fix this please?

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If there isn't already, there should be a video tutorial on how to resize up or down a document. Seen everything under the sun without really understanding this process.

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As you may know, "TIFF" is an abbreviation for Tag(ged) Image File Format. From that, you might expect it to define a tag for an image's dpi value, but it is more complicated than that. There are 3 tags that indirectly define an image's default dimensions based on its pixel resolution. They are:

 

• X Resolution -- the horizontal resolution in pixels per unit

• Y Resolution -- the vertical resolution in pixels per unit

Resolution Unit -- The units used for XResolution and YResolution

 

The Resolution Unit can only be one of three values: 1 for none or not defined, 2 for inches, or 3 for centimeters. The X & Y parameters can be any rational number. Note that only if the Resolution Unit parameter is 2 or 3 and the X & Y parameters are identical would a single number unambiguously define a dots per unit (inches or centimeters) parameter.

 

If both conditions are true, with just a little math an application can easily derive a dpi number from the three tags, but that is almost irrelevant because as you will find mentioned in references like this one & this one for X Resolution & Y Resolution respectively, there is no requirement that an application must display or print the image at the size implied by those tags. An application is free to use this information any way it wants, including ignoring it completely.

 

Consider for instance Affinity Photo or Designer, Adobe Photoshop or Lightroom, Apple's Preview or Aperture, or just about any browser app in existence. All can display tiffs at various sizes. Some even allow the user to choose one of several default sizes for the "actual size" display setting. Likewise, printer drivers & printers may change the printed output's dimensions to allow for non-printable margins, scaling, multiple copies per sheet, etc.

 

So my advice is to concentrate on resolution (in pixels), not dpi. 


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First of all, If dpi was indeed of no great interest then there would be no reason for Photoshop or A.P. to include the ability to set it, and they have. Secondly if you have worked with DTP applications you know that if you insert for example a 4000 dpi scan of a slide in a 16x20cm box it will look terrible on screen because (at least in QuarkXPress) the software needs to blow it up about 400%. The file has more than enough pixels, but the application looks at print size which with 4000 dpi is tiny. So I do not think we need neither a complex tutorial on something as mundane as changing the dpi of an image nor a technical brief on file formats. Affinity just needs to fix A.P. so that what you set in the dialogue is also what is exported to other file formats. I am no power user, I mostly work with normal retouching and archive scanning, but A.P. has some basic faults that make me fall back on PS again and again. I might just be unlucky in that two of the things I need are the only two things that still need work (jpegs look worse than the same file exported from PS (kills A.P. for creating crisp thumbnails of products for lets say a web shop), and then there is this resolution thing which kills A.P. for (my) DTP use). If you work solely with applications that do not take dpi into account, then A.P. is perfect just the way it is, but that doesn't mean it shouldn't be fixed for those who actually need it.

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First of all, If dpi was indeed of no great interest then there would be no reason for Photoshop or A.P. to include the ability to set it, and they have.

I think Photoshop Help /Image size and resolution is worth a read.

 

Also, What is DPI? & Adobe Photoshop Image Size Dialog Box by Ken W. Watson. 

Edited by R C-R

Affinity Photo 1.9.1, Affinity Designer 1.9.1, Affinity Publisher 1.9.1;  2020 iMac 27"; 3.8GHz i7, Radeon Pro 5700, 32GB RAM; macOS 10.15.7
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Just a thought, what version of AP are you using, in earlier versions, there was an issue where resized files were not displaying dpi correctly in other applications such as Preview & PS.  Apparently this was due to the meta data not updating in AP exports, in current versions this is fixed.

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I think, when Affinity releases its publishing application, it will be taken more serious, that the user wants the dpi values, he has been assigning to his images, be respected.

Just try to place a 72 dpi image of a modern 20 MP pixel cam on an A4 page (instead of using a 300 dpi image) and you will see, how weird this discussion is: This image will will be placed with 72 dpi and about 197 x 133 cm width x height! Much fun by placing such gigantic images with way to low resolution within a – let's say – DIN A4 flyer. Happy zooming and scaling!

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Hey, Could we re-open this thread? Ok so I have a picture at 5760 × 3724 pixels at 300 dpi.

@R C-R, I read all your articles, I understand what they say, but it contradicts what I've heard: I've heard that in web, you should only upload 72 dpi, 300dpi is for print.  And I don't know who says that DPI, for digital photographers,is not that important, you should focus only on hight and length. I don't understand why because it does affect quality a bit.. BUT ABOVE ALL, THE WEIGHT OF THE FILE!!!

 

I was able with pixelmator, to transform that same picture (5760 × 3724 pixels at 300 dpi) at 1382 × 894 pixels 72 pixels/inch AND 1382 × 894 pixels at 300 dpi.  with Affinity, it's impossible, I think there is a bug.

 

Can we comment on this?
 

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I've heard that in web, you should only upload 72 dpi

 

That is frequently stated, but it is incorrect. Your computer screen doesn't care about DPI: it only knows about pixels, so (as R C-R said) you should concentrate on resolution in pixels.

 

The 72 dpi figure comes from the old display setting of 72 pixels per logical inch on a Mac (cf. the standard Windows resolution of 96 pixels per logical inch). The pixel density on modern retina displays is, of course, very much higher.


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I've heard that in web, you should only upload 72 dpi, 300dpi is for print.

That isn't just incorrect, it is also almost meaningless unless carefully applied to very specific contexts. To understand why, it might be worth browsing through the three Wikipedia entries for Dots Per Inch, Pixel, & Image Resolution to get an idea of the several different things each of these terms can refer to.

 

For example, both "pixel" & "dot" can refer to several different spacial measurements, each unambiguous only if applied to the appropriate display or print technology, properly referenced to the specific characteristics of both the hardware & software used to create it.


Affinity Photo 1.9.1, Affinity Designer 1.9.1, Affinity Publisher 1.9.1;  2020 iMac 27"; 3.8GHz i7, Radeon Pro 5700, 32GB RAM; macOS 10.15.7
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I too have found Image Size dialog quite buggy. I hope it gets fixed soon.

Buggy in what respect?


Affinity Photo 1.9.1, Affinity Designer 1.9.1, Affinity Publisher 1.9.1;  2020 iMac 27"; 3.8GHz i7, Radeon Pro 5700, 32GB RAM; macOS 10.15.7
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Buggy in what respect?

Without resample checked you cannot set size in mm, cm etc.

DPI value can be set but it does not update to size values.

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Without resample checked you cannot set size in mm, cm etc.

DPI value can be set but it does not update to size values.

That's because unless you resample the image you are not actually changing its size. If this still seems confusing, the articles I posted the links to in my 11 March replay may help with that. Also check out the Affinity "Understanding DPI" video tutorial.


Affinity Photo 1.9.1, Affinity Designer 1.9.1, Affinity Publisher 1.9.1;  2020 iMac 27"; 3.8GHz i7, Radeon Pro 5700, 32GB RAM; macOS 10.15.7
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Does here nobody understand, whats the problem? Reading this weird thread, I think, it is better to give up …

For all, who think "unless you resample the image you are not actually changing its size":

• Look for someone, who has InDesign or QuarkXPress on his machine.

• Create 2 images: (1.) 2480 px x 3508 px, 300 dpi and (2.) 2480 px x 3508 px, 72 dpi

• Place the two images in one of these layout applications by clicking with the "loaded" cursor onto your canvas.

• There is nothing more to say, except one thing: If you have a picture heavy design and you use images of type (2.), I think you’ll never create a layout any more … Why? If you don’t know or don’t see, you never ever have dealt with desktop publishing …

 

… and one more annotation:

• Place an image of type (1.) in a layout application and save it. Examine the file size of this document.

• Place an image of type (2.) in a layout application and save it. Examine the file size of this document.

• You see the difference?

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That's because unless you resample the image you are not actually changing its size. If this still seems confusing, the articles I posted the links to in my 11 March replay may help with that. Also check out the Affinity "Understanding DPI" video tutorial.

Sorry but you did not quite understand the problem. Physical size should change according the dpi value when resample option is not selected. PS handles this right, AP does not update correct values.

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The problem, such as it is, is that DPI is relevant only to printed output, & even for that printer driver and/or application settings may use a different effective DPI for printing.

 

For instance, in mac_heibu's example, both images have exactly the same number of pixels. Apps can display either one at a variety of different sizes on screen. Some apps even have more than one selectable default settings for the "actual size" display setting. Likewise, a printer driver must convert "dots" to whatever type of micro-structure printing elements the printer uses, which varies considerably depending on the printing technology. For everything other than an old fashioned dot matrix printer that does not result in a 1:1 correspondence between dots & what the printer puts on the paper or other print media, in the same way that there is no 1:1 correspondence between screen pixels & image pixels.

 

Moreover, modern OS's like Windows & OS X & many apps are quite capable of rescaling printed output such that the effective DPI of the printed output may be higher or lower than the "native" DPI of the image.

 

Finally, different apps store image data differently, which can dramatically affect file sizes. Some include multiple copies of images at different resolutions, for example to accelerate on screen rendering at different magnification ("zoom") levels, or include copious amounts of metadata to support proprietary features other apps can't use but they may preserve for portability reasons.

 

The bottom line is "dots" & "pixels" not only measure different things, each of them can mean different things depending on context.


Affinity Photo 1.9.1, Affinity Designer 1.9.1, Affinity Publisher 1.9.1;  2020 iMac 27"; 3.8GHz i7, Radeon Pro 5700, 32GB RAM; macOS 10.15.7
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1.9.1.225 & Affinity Designer 1.9.1 (showing 1.9.7) for iPad; 6th Generation iPad 32 GB; Apple Pencil; iPadOS 14.4 (18D52)

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Sorry but you did not quite understand the problem. Physical size should change according the dpi value when resample option is not selected. PS handles this right, AP does not update correct values.

Physical size only has meaning for physical media like printed output, & even for that an image's "native" DPI may or may not define its physical size.


Affinity Photo 1.9.1, Affinity Designer 1.9.1, Affinity Publisher 1.9.1;  2020 iMac 27"; 3.8GHz i7, Radeon Pro 5700, 32GB RAM; macOS 10.15.7
Affinity Photo 
1.9.1.225 & Affinity Designer 1.9.1 (showing 1.9.7) for iPad; 6th Generation iPad 32 GB; Apple Pencil; iPadOS 14.4 (18D52)

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• There is nothing more to say, except one thing: 

There is also the fact that it is very easy to check if the resolution is enough for planned print size when you have correctly working image size dialog. For example you plan to print 1400X1000 mm size exhibition piece and when you put those values to size dialog you get dpi value: if it is below 300 dpi you may have to reconsider the print size..

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