Bitmap import scaling wrong in omacOS

Good morning

For a simple project I scanned some wooden spoons and save parts of the scan as TIFF, PNG and JPEG…

All images can be imported in Affinity Designer and scale correctly with each image being 60mm x 85mm (Here shown palced on an A4 sheet):

Bildschirm­foto 2022-11-24 um 09.18.04

But when I import those images into LightBurn they are all scaled wrong (here placed on 420mm x 180mm sized machine):

LightBurn imports them always at 72pixels/Inch…

So when I scale the image in the Preview App on macOS to:

Bildschirm­foto 2022-11-24 um 09.26.53

Lightburn imports it at size 249mm x 352mm:

This is very annoying to work with any kind of images in Lightburn as I have to open every image in Preview App and scale the image to be 72dpi.

I don’t think I’ve seen that behavior before on the forum and I don’t have a problem with DPI not being respected on import.

How have you scanned the images? Are they being processed before import at all?

Can you upload a sample file here?

Here’s a sample image that should import at about 100x100 mm. It is 300 DPI. Can you try loading it and seeing what you get?

This is how it looks on macOS 13.0.1 in LB

It is shown as being 416.6mm x 416.6mm as it is imported as 72dpi, which is exactly 4.1666 times bigger (300 / 72).

Attached a JPEG exported as 300dpi from macOS Preview App:

Imported as 125x176 mm. What was the expected size?

Not sure why your system is not respecting the DPI data. I don’t recall seeing that on Mac when I last used it. Has this always been a problem?

Affinity Designer shows on import:

Width: 59.9mm
Height: 84.5mm

So Affinity Designer is interpreting the image as 300 DPI. Looks like LightBurn is interpreting it as 144 DPI (at least on my system). Oddly, I’ve checked the file with a couple of different methods and one shows it as 72 DPI, and the other as 144 DPI.

I suspect the file itself is either ambiguously or improperly defined.

But it seems there are multiple things going on in your particular case:

  1. Somehow your LightBurn is interpreting things consistently at 72 DPI
  2. The files you’re working with may have an issue with header definition

I’m not sure what could affect the first scenario. I haven’t seen that. It’s odd.

For the second, you may want to check a few other mechanisms to generate the files to see if you get a different outcome.

This video explains a lot about using Affinity Designer. Near the end (around the 30 min. mark) it goes into the correct settings for exporting your file for use with your laser. This may have something to do with the scaling issue.

Both Paint dot Net and LightBurn see that image file as 96 DPI, and 12.03 inches square.

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Affinity has a “project level” DPI setting that I believe it uses for everything, so it’s quite possible that when you save, it’s saving the images with that DPI setting, not whatever the original was.

LightBurn reads the DPI value from the source file, and imports accordingly. If you save an image from PhotoShop, CorelPaint, Paint dot Net, or any other software that properly writes the DPI values into the file, it will import properly in LightBurn.


But why does the suggested test image don’t even scale correctly on macOS?

This has nothing to do with Affinity…

And as mentioned…the image was exported in the Preview App and imported correctly in Affinity Designer…not exported from Affinity Designer…

Now I’m even more confused.

I just reimported and it’s showing 3.9367 inch square. I designed in inkscape at 4 inches and exported to PNG at 300 DPI. Installed to compare and also shows up as 3.94 inch square. So all apps in my world are consistent.

Windows 11
Display is 2240x1400
150% scale
High DPI scaling override by Application for LightBurn

It’s entirely possible that the version posted to the forum was altered by the forum software. Sometimes these systems will re-compress images for space. Regardless, your source version is consistent across all the apps including LightBurn, so that’s really what counts here.

Odd results indeed but can’t reproduce what you guys are getting.

  1. Right-clicking and using “Save image as” or “copy image” result in 5.2 inch square
  2. Right-clicking and using “Save link as” results in 8.2 inch square.

I suspect there may be user specific scaling going on. That at least explains the discrepancy.

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