Why are my highlights purple?

Question

I was shooting a subject that featured a lot of sunlight shining across a surface. In some of the photos, the sunlight appears to have a purple tinge to it. In others, the colours are more natural.

Compare this: f/5.6 1/125s ISO100 55mm

With this: f/16.0 1/60s ISO400 55mm

I'm pretty sure it isn't chromatic aberration because this isn't around the edges of the highlight area, it's the whole area. It looks like a sensor saturation issue to me.

EDIT: To clarify, I am using the same manual white balance settings for both.

EDIT: Sorry, I had put the wrong aperture and ISO for the second photo. I have corrected it now.

EDIT: I took a few photos with the camera settings as the first photo and they all had purple highlights. I also took a few at f/22 1/60s ISO800 and none of them had purple highlights. I'm guessing the difference is due to either the smaller aperture or the higher ISO.

Answer 1

Highlights are a difficult part in digital photography because the image information gets blown out in highlights rather abruptly, as explained in the question, Why are blown highlights particularly bad in digital photography?

Briefly speaking: any RGB-value can only reach 255 and is capped afterwards, whereas in film a softer transition with more texture in white areas is possible. The linked example explains this for whites, but in your case you have to imagine the 3 RGB color-channels seperately. The area around your highlight can get these colour tints, if individual channels get 'blown out' i.e. capped at a value of 255 before the others. Ken Rockwell briefly touches this subject in his article, Adding Dynamic Range to Any Digital Camera, which might help you fix the problem.

You will have to watch your histograms while shooting and try to avoid any channel from getting blown out. This means you have to correct exposure while shooting, which will probably result in a slightly underexposed image which you can then brighten in post-processing. Not great, but the only workaround I know of. You'll have to decide, wether the barely noticeable effect is worth the effort.

Answer 2

The problem with the raw file is that it is clipped not at highest possible level but at something like 80% of highest level. Any program will make the highlights of such a file pink because of white balance which should be applied (most cameras' photos has strongly greenish tint before correction).

Judging by that it is present in RAW file I can only say that it is a camera bug (and I did not see bugs like this before). Your only possible solution is to update the firmware or to report the bug to the OEM.

The easiest way to fix it is to set positive exposure correction in raw developer: there is no information in that area anyways.

Answer 3

As i can see in the picture and have experienced the same thing in my photography , it happens due to a very minute difference in the angle from which the image is taken , and as in case of your's it is because in the pic with purlpe effect the focus is on the object where as in the other one the focus is on the white part/sky or whatever that portion is.