How do I stop Preview from automatically brightening my images

Re: How do I stop Preview from automatically brightening my images :

This mainly happens for images imported from my iPhone (taken as High Efficiency format).

Thank you for your post to this (user-to-user) community, and for the details and info. you have shared.

Am no expert on this topic, yet your question certainly deserves some response, if only to provide more opportunity for others with more expertise to join in.

Wondering if there is some kind of colour-profile set up.

Apple Support's article: Apply a color profile to an image in Preview on Mac - Apple Support

Eg: says:

"You can apply a Quartz filter to an image in Preview so the image’s colours are more faithfully reproduced on printers, displays and other devices.

1. Go to the Preview app  on your Mac.
2. Open the image you want to adjust.
3. Do one of the following: 

• • Apply a colour profile to the image: Choose Tools > Assign Profile, select a colour profile, then click OK.
  • See what an image would look like on a different device: Choose View > Soft Proof with Profile, then select a colour profile.

The ColorSync Utility in macOS manages the colour profiles used by connected displays and cameras."

According to the guidance and info. available in the linked Resource below:

Seems you can "Get consistent colours across devices : Use colour profiles to make sure the colours in your images appear the same on all your displays—and when you print"

ColorSync Utility User Guide for Mac - Apple Support

Other Resource: Preview User Guide for Mac - Apple Support

Do the images by chance use Rec. ITU-R BT.709-5 profile in the .heic?

Sequoia seems to have some issues with it (see the link below). If I use Preview.app > Tools > Assign Profile... > Rec. ITU-R BT.709-5 > OK > Quit Preview.app (then re-open the .heic and verify that the profile has been added because Preview does not always update it as expected -- 'exiftool -a -G1 -s -ProfileDescription image.heic' might display it updated while Preview does not).

Then QuickLook displays some artifacts and Preview has a split second change when opening the image.

Personally I have not had trouble with that and I don't use Preview for any serious image work anyway because it has some issues and bugs. See also:

Gamma shift when using Save Current Frame… - Apple Community

plzpsd wrote:

Many thanks. I tried saving the problem images as both Quartz filter and New Assigned Profile (e.g. ACES CG linear) as suggested, and delighted to say that this then stopped the 'automatic brightening' in Preview.

interesting... with no interaction on my part, that is the default setting on my macOS 15.5 and never had an issue

Thank you kindly for taking the time to reply, and for sharing your experience with us. Grateful to know you found a way that works for you! Cheers!

Re: "I'm still mystfied though why this auto brightening in preview started occurring as I have a standard Mac M1 pro and iPhone 15 Pro set up. As you say could be a Colour Synch issue but late at night now to check... "

Am using an earlier MacOS version, so am unable to check default settings (ie: from top menu: Preview > Settings ) to see if anything set there would explain, and /or could be changed.

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Thank you 😉

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