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I'm trying to fix some old (as in a few years old, not vintage) images taken by a friend, and have noticed something odd. While most of the pictures appear somewhat over exposed/have strange colours (possibly due to an effect implemented by the digital camera at the time), the thumbnails in each and every case are perfect (I've managed to extract the thumbnails as separate JPEG's.)

As such, is there a straightforward way or methodology for fixing the larger pictures using the thumbnails as a reference point? (Ostensibly for colours etc.) I have access to Photoshop but haven't used it extensively for many years (and even then didn't really use it for retouching work, at least not this sort).

Thanks.

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I can't tell for Photoshop (but I assume the method would be similar). In Gimp I would do:

  • open the full scale image
  • add the thumbnail as an additional layer
  • scale up the thumbnail so that it exactly matches the full-scale image
  • set the thumbnail layer to "Color" blend mode

Rationale: the detail we perceive in the image is more due to luminosity than to color. With the method above, you create an image that takes its luminosity (and therefore its detail) from the full-scale image, and its colors from the thumbnail.

  • Going to +1 this but I'd worry that some hardcore pixelation of the thumbnail may cause some unintended side effects no the color blend. Fuzzy borders and what not? – Hueco Jun 30 at 20:45
  • In practice you don't care. There can be some color bleed but it's hardly noticeable. This is how most PEGs are encoded, the color information is kept in a pair of channels that are 2 or 4 times smaller than the Luminosity one. – xenoid Jun 30 at 23:16
  • Thanks xenoid, this didn't work perfectly but DID get me much closer to the proper colours/light levels as requested, so looking good as a start. Much appreciated (also, you were correct in that there was no noticeable pixelation). – Dude Jul 1 at 22:22

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