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I was looking through some photos I took at RAF Cosford a few weeks ago, and noticed this big red area (it's a large door surround on the floor below)

In the photoshop RAW preview, it looked almost like it was a highlighted area, but when i opened the image fully, no, its just part of the image.

It looks very un-natural to me, it appears almost better focused than the posters and door logo, but it is at the same distance. could this be a wavelength difference?

It also looks a bit blown out, which may well be part of the issue.

enter image description here

enter image description here

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  • \$\begingroup\$ What camera, i.e. sensor? Possibly the area was painted with luminous paint. \$\endgroup\$
    – feklee
    Commented May 6, 2013 at 13:13
  • \$\begingroup\$ Nikon D800 with Nikkor 1.4f AF-S No, it was red, i remember standing next to it! \$\endgroup\$
    – Digital Lightcraft
    Commented May 6, 2013 at 13:17
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    \$\begingroup\$ No, it was red I don't dispute that. Red luminous paint ("DayGlo") is brighter than normal red paint. This is because it reflects not only the red frequencies of incident light, but it also converts other light frequencies to red. \$\endgroup\$
    – feklee
    Commented May 6, 2013 at 13:40
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    \$\begingroup\$ It converts other light frequencies? That sounds interesting. Could you please post a link to an explanation for that? \$\endgroup\$
    – Saaru Lindestøkke
    Commented May 6, 2013 at 14:23
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    \$\begingroup\$ @BartArondson: That's fluorescence, the property of absorbing high-energy photons and re-emitting them as lower-energy (longer wavelength) photons. In a fluorescent light bulb, for example, the coating converts UV light into the visible range. DayGlo paints work similarly. \$\endgroup\$
    – coneslayer
    Commented May 6, 2013 at 14:32

4 Answers 4

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As Guffa said, the red channel is blown. All the RGB values are (255,0,0)

In the other red parts of the image, it's more like (190, 35, 40) and all the red, green and blue luminance values fluctuate and there is some texture/detail/noise.

enter image description here

Histogram of the blown area:

enter image description here

And of the nearby red area:

enter image description here

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Yes, the red light is totally blown out, and that is simply the whole issue.

It looks to be more in focus, because you are seeing the point where it gets clipped as an edge. The blown area looks flat, and the edge around that area looks like it is almost in focus.

We are used to seeing areas where all color components are blown out to white, not so often where a single component is blown out like this.

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Possibly the area was painted with fluorescent red paint, also known by the brand name Day-Glo. Standard red paint just reflects the red component of incident light. Fluorescent red paint in addition converts high frequencies (UV) to red, thereby boosting brightness.

High brightness can cause overexposure, in this case in the red channel. To avoid that, keep an eye on the color histogram when taking the picture.

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Your seeing visual clipping. The way that the camera exposed the image, the Red channel was brighter than the camera could capture there. You've probably seen this kind of thing far more commonly with generally blown out spots where you get white highlights that all details is lost within. In this case, it just happened that it only blew out on the red channel. If you were shooting RAW, highlight recovery may be able to salvage it. To avoid it in the future, it would be necessary to adjust exposure to avoid clipping.

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  • \$\begingroup\$ Yes i was shooting raw, i had a quick play and it did help a bit BUT then the rest of the image was knackered. to be honest im not bothered about the image at all its not "good" - I was just intrigued by the unusual nature of the red bit :-) \$\endgroup\$
    – Digital Lightcraft
    Commented May 6, 2013 at 13:20
  • \$\begingroup\$ @DarkcatStudios, in Lightroom (and so I would presume ACR as well), I would start by going to the HSL panel and decreasing the red luminance (and maybe saturation). \$\endgroup\$
    – coneslayer
    Commented May 6, 2013 at 14:36

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