Today’s Question: Why did a photo with many layers flatten when I needed to Convert to Profile in Photoshop’s latest version? The original image was a slide scan from a Nikon scanner profile. I needed to convert it to ProPhoto RGB and when I did, all the layers disappeared leaving only the base layer.
Tim’s Quick Answer: The image was flattened because you left the “Flatten Image to Preserve Appearance” checkbox turned on in the Convert to Profile dialog. You can keep this checkbox turned off if you want to retain the layers when converting the image to a different color profile.
More Detail: When you convert an image from one color profile to another, there is a risk that you will lose some color fidelity in the process. This is in large part because some colors that are available in your source color profile may not be available in the destination color profile.
In addition, the process of converting an image from one profile to another can cause a small degree of change in the color appearance of the photo. This is generally not significant, but it is possible. Turning on the “Flatten Image to Preserve Appearance” checkbox will help reduce these issues, by removing any adjustment layers and image layers that might cause variability in the final effect, based on how those layers impact the underlying image data.
In most cases I am perfectly comfortable leaving the “Flatten Image to Preserve Appearance” checkbox turned off. The change in color in the image will generally be extremely minor, and generally not visible within the image.
If you are concerned about a color shift when converting an image to a different color profile, I generally recommend creating a flattened copy of the image rather than flattening your master image. To do so you can choose Image > Duplicate from the menu. In the Duplicate Image dialog you can turn on the “Duplicate Merged Layers Only” checkbox so that the duplicate you’re creating will be flattened. You can then convert that duplicate image to the desired color space and continue working with that copy of the image as needed, preserving the original master image with all layers intact.