PPI - (not the difference with DPI) can you control ppi?

[Jim Holdings]

I have a requirement to produce images at 500ppi (not DPI. I know they are different but as these images are not printed i dont really care about DPI). I can not seem to find any method of doing this when re-sizing. The camera (Nikon)id importing a RAW file with a huge PPI but on resizing all is lost. I can only seem to select a DPI on resizing as a maximum of 300 DPI. Im new to Afinity and know I could do all this wen resizing in PS. Thanks in advance for help

[toltec]

 

48 minutes ago, Jim Holdings said:

I have a requirement to produce images at 500ppi

The trouble with using inches for images, is what size is your inch ?

Lets take a (so called) one inch image at 500 pixels per inch. It will contain 500 pixels.

500 pixels on a  27" 1920 x 1080 monitor will be displayed at about 5 inches wide

500 pixels on a phone will be displayed at about 1 inch wide.

So using inches on your 500 ppi image will only be useful if you are creating the image for a basic phone. 

 

Best to work in number of pixels only and ignore inches.

If you need to use inches to work something out, say a three inch image at 500 pixels per inch, you need to end up with 1500 pixels. There is no effective difference between DPI or PPI so you can use the DPI box to work it out for you.

See 3 in x 3 in with 500 set in the DPI box. With "Resample" ticked 

click on Resize and it will create a 1500 pixel image

Which is 500 pixels per inch.

 

But it still leaves the problem that an inch will not be an inch on the device, unless it's an average phone.

 

[R C-R]

1 hour ago, Jim Holdings said:

I can only seem to select a DPI on resizing as a maximum of 300 DPI.

I am not sure why you think this. The DPI slider in the Resize Document window goes up to 400 but you can enter any number in the DPI field directly, including ridiculously large ones like 2000 that together with the resampling option can create so many pixels that your computer will beg for mercy! 

You may also find it useful to review the Understanding DPI video tutorial if you have not done so already, particularly the part about pixel resolution (which I suspect is what your requirement might be about).

[toltec]

15 minutes ago, R C-R said:

you can enter any number in the DPI field directly

Good point. I forgot to mention that I had typed 500 in the box.

[Jim Holdings]

Hi

Thankyou for your replies. Unfortunately our requirements are very specific, we need to produce TIFF images 1:1 at 500ppi and they are not specifically for printing which when we do we do, it at 300dpi. Is it possible to set such paramenters in Affinity? 

[toltec]

34 minutes ago, Jim Holdings said:

Hi

Thankyou for your replies. Unfortunately our requirements are very specific, we need to produce TIFF images 1:1 at 500ppi and they are not specifically for printing which when we do we do, it at 300dpi. Is it possible to set such paramenters in Affinity? 

Well, yes. Type 500 in the DPI box. It's the same as PPI. I am just not sure if the 500 dpi (or ppi) setting will be recognised by the final device/software. You would have to try that. It would however be the correct size/ppi.

[R C-R]

• First, a little background info:

In TIFF images, pixel dimensions are specified using three tags, XResolution, YResolution, & ResolutionUnit. This is because the TIFF format is capable of supporting non-square pixels (where the X & Y resolutions are different) & images that specify no absolute dimensional units, as well as one that specify dimensions in either inches or centimeters. Many graphics apps assume TIFF images have square pixels & display a single "DPI" value based on the resolution unit & the X or Y resolution value. For example, this is what the Apple Preview app's Inspector panel might show for a developed Nikon RAW image file exported to TIFF:

• So with that in mind:

This works with Affinity Photo TIFF exports as @toltec suggested by typing 500 in the DPI box (that is how I made the above file), but because of a bug in Affinity, EXIF metadata is not updated when the document is resized. So for this to work you must either uncheck "Embed metadata" in the Export > More window or after exporting the file use some other app to change the X & Y resolution units to 500 (& make sure ResolutionUnit is set to 1) if you need to include all the EXIF metadata in the TIFF file.

Also note that for many uses the derived DPI/PPI and ResolutionUnit values are irrelevant because the image may be used at a different resolution based only on its pixel dimensions (which is one of the reasons why they are specified using the three tags).