Trivial phenomena -> Science -> Homeclick!

Cette page en franšaisCliquez!

Trivial phenomena:

Pink artifact on digital photographs:

A gentleman submitted a series of pictures to a ufology discussion list, asking for explanation. This is my explanation.

Lens reflections

The pink - purplished traces are an internal reflection of the sun in the lens.

The sun can be missing from the image: what the lens reflects is the part of the rays of the sun striking the lens outside the boundaries of the CCD area itself and bouncing in, either because the lens system is complex, including a zoom lens for example, or because a lens has some tiny surface defect, without effect in other circumstances - these factors being additive.

The color of such reflections is typically pink, purple, on digital camera and digital video camera and webcam pictures.

The reason is that most digital camera automatically adjust the color balance.

The camera looks at the relative amounts of the primary colors in the scene, and then try to adjust the color to make things look "real". If you take a picture in the open where the illumination comes from the blue sky, the camera reduces the brightness of the blue sub-image and increases the gain for the red.

With the above picture, taken with an E5700V1.1 Nikon Coolpix camera the EXIF data indicates: "WHITEBAL: SUNNY", the preset for blue sunny sky images. The camera was on a tripod and a dozen other pictures were taken next in that position within the next 7 minutes, all showing the same artifact.

Such artifacts can be avoided by using a sun hood, or putting one's hand in an appropriate position between the camera and the sun.

Below: several types of sun hoods to prevent such artifacts.

Sunhood Sunhood Sunhood Sunhood

Correction and new information!

Thereafter, the photographer indicated that actually, he had reported previously, information that was forgotten: the pinkish features were caused by a damaged caused by overusing the camera to take direct photographs of the sun without protection, and this damage had apparently become permanent, the pinkish artifacts remaining. He indicates that he was going to change the camera.

He explained that what had actually intrigued him on those pictures was not what his readers assumed, it was not the pinkish artifacts but some objects in the sky on one of the photographs.

I thanked it for the information and asked to whether he could send over another photograph taken some other day also showing the pink artifacts.

Then, I tried to determine which objects exactly must be explained, since it was not the pinkish artifacts. The only objects in the sky I can see in the series of photographs are, to me, all birds.

As the photographer indicated "in the bottom on the left in the series," I circled both object in the sky on this image, and asked him to specify if this is indeed what he is asking about:

As for these things which I circled, to me, these are birds.

Here is my interpretation for these two birds:

This is why his two readers who put forth or discussed an explanation thought they had to explain the "pink streaks" whereas it was not what had puzzled him! The objects in the sky, were to me in any case birds, and it never occurred to me that this could be what required explanation!

I explained to him: "We all are different people, [firtsname], what puzzles you is not inevitably what puzzles your reader."

At this step, it is not obvious that I understood exactly which objects of the series of photographs puzzle him. For the two I circled, from photograph 13, the photographer answered me that indeed it is this kind of object that puzzle him, but not exactly these two on that photograph, others that also resembled birds, but not these.

I thus numbered his series of photographs:

And I asked him to tell me the number of the photograph where precisely the objects I should explain are located. Once this is established without risk of new misunderstandings about what must be explained, I will try, by circling, to understand exactly which are the objects that require explanation.

So, this is to be continued.

Note: all the above was written on May 23, 2008. As of January 2009, the gentleman still hasn't answered my question.

Valid XHTML 1.0 Strict

 Feedback  |  Top  |  Back  |  Forward  |  Map  |  List |  Home
This page was last updated on May 23, 2008