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Night shoot - what's causing the randon blue & red pixels?

peskywinnets

Active Member
Just got back from the in-laws who live deep in the country in the south of Brazil.

They live in a forest which comes alive at night with fireflies. On my last night there, I thought it'd be fun to try & photograph them (alas, no tripod, just used the bonnet of the jeep...& I only had about 10 mins - an unsuccessful photoshoot in this instance!). Anyway, to the point of my post, when I looked at the (poor) photos on my PC, apart from the odd bright green blob of fireflies on the move, there are some static red & blue random pixels spread throughout the photo. On each photo these are in the same position, I never noticed them before except on these particular nightime shots.

Here's an example (green blob is one out of focus firefly on the move), have a look towards the bottom left quarter of the photo where the red & blue pixels I'm on about are more pronounced.




Any idea what's causing these?

If it helps, I was using long exposures of about 4-8 seconds & a high ISO setting of 1600.


Just for fun, a bit more info on the wee beasties, in Portuguese they're called vaga-lume - my father in law caught a couple & here's what one looks like (ok, so it's a soft photo, but this was all shot in very low light without a tripod & they move rapidly!)...



Those green lights aren't its eyes...they're way up front, but on the back of its head.

& here's a one on a table walking about...



Abstract or what?! I was tempted to post the photo above up & ask if anyone could guess what it is!!!

I'll nail a good shot next time I'm over there, as it was all a unscheduled/unplanned & shooting from the hip, so to speak.

If you ever get the chance to see similar beasties en-masse I'd certainly recommend it - it really is a wonderful experience in the pitch black having silent flying fluourescent green LEDS flying all around you!!!
 

bishbashboshdj

Well-known Member
I couldnt see any of the red and blue pixels but i have had this on a shot ive done before, its caused by refraction of the light in that pixel..... the only way i know to get rid of them is retouching :thumbsup:
 

peskywinnets

Active Member
I couldnt see any of the red and blue pixels but i have had this on a shot ive done before, its caused by refraction of the light in that pixel..... the only way i know to get rid of them is retouching :thumbsup:

Thanks...they're difficult to see as the forum resizes down to fit on forum (if you click save picture as & then open it outside of a brwser they're easiser to.

I've circled them in orange here...




what you're saying makes sense, as thinking about it, these red blue spots are actually too big to be single pixels. The original size of the photo is 3456x2304 & I can see them clearly without zooming in, therefore whatever is causing it must breach across a lot of pixels so refraction sounds feasible (or maybe the result of dust on the lens or sensor?)
 

Brammers

Banned
I couldnt see any of the red and blue pixels but i have had this on a shot ive done before, its caused by refraction of the light in that pixel..... the only way i know to get rid of them is retouching

Not quite right there sim - these are 'hot' pixels, caused by your camera's sensor heating up during long exposures.

2 ways to get rid of them, PP as you say, or, if it's turned off at the moment, the long exposure noise reduction facility.

If you are going to PP, then make a 'pixel map'. Shoot the inside of your lenscap for 30seconds and use the resulting 'map' to discover the locations of all the hot pixels. Some programs or photoshop techniques will then automatically correct these, what software have you got?
 

Yandros

Well-known Member
Yep, I think all sensors do this to some degree. At normal ISOs this doesn't happen, but at 800ISO+, they start popping up.
 

T0MAT01

Well-known Member
It's just a bit of noise from using ISO 1600, nothing to worry about.
If you run it through a program like neat image (it's free - have a search) then it'll wipe it clean for you.

As an aside, I prefer to shoot in RAW when using high ISOs since it is easier to clean them up before they're turned into a jpeg.
 

bishbashboshdj

Well-known Member
Not quite right there sim - these are 'hot' pixels, caused by your camera's sensor heating up during long exposures.

There is an issue where you get refraction of light in pixels, ive had it before when i was studying at uni and was assured thats what it was, i think it effects older ccd's though, it happened to me on the 5 megapixel nikon DSLR that was out in the old days...... you can barely see the pixels i only noticed it when i was retouching but they were perfect pixel shaps in purple and pink
 

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