What Causes Small Red or Blue Pixels in My Photo
why are there red, blue, green dots in my photos?
I took some photos a month ago, that I am not working on in Photoshop at high magnification. These photos have tiny little dots that are each brightly colored red, green or blue. there are 30 or 40 of them in most frames. In one frame, a frame that was underexposed and I applied a lot of correction via Photoshop Curves, there were over a hundred of them and they were more pronounced. You can see what I mean with a screen capture I captured when zoomed in at 700 percent., go to
all photos shot inside of a Gufstream airplane that day exhibit these dots. no photographs before or after exhibit these dots. They are in all frames I shot that day inside the airplane. I took about 200 captures at 4256 x 2856 with camera set at 800 asa.
does anyone know what could have possibly caused these dots to appear?
At first I thought my CCD was going bad and I would have to either have it replaced (my warranty expired 2 days ago), or I would have to have the CCD "re-mapped" (someone's elses suggestion... not sure if he was right or wrong.)
why would this only happne on this particular day.
It was a rather pleasant summer day. the airplane was in the hangar. the electricity was turned on, and the airplane was plugged into the wall of the hangar... or to a service cart, not sure which. there was a portable air conditioning unit outside the airplane with a long duct running up to the door of the plane to keep me cool.
I have shot similar airplanes in similar conditions, with the Air conditioning set up.... and never experienced these red blue and green dots before.
anyone have an idea what caused them so I can avoid them in the future. I had to do a lot of cloning to get rid of them all.
thanks
Christopher
Tuba Paul • Senior Member • Posts: 1,148
Electrical interference? (nt)
Christopher Mann wrote:
I took some photos a month ago, that I am not working on in
Photoshop at high magnification. These photos have tiny little dots
that are each brightly colored red, green or blue. there are 30 or
40 of them in most frames. In one frame, a frame that was
underexposed and I applied a lot of correction via Photoshop
Curves, there were over a hundred of them and they were more
pronounced. You can see what I mean with a screen capture I
captured when zoomed in at 700 percent., go to
all photos shot inside of a Gufstream airplane that day exhibit
these dots. no photographs before or after exhibit these dots. They
are in all frames I shot that day inside the airplane. I took about
200 captures at 4256 x 2856 with camera set at 800 asa.does anyone know what could have possibly caused these dots to appear?
At first I thought my CCD was going bad and I would have to either
have it replaced (my warranty expired 2 days ago), or I would have
to have the CCD "re-mapped" (someone's elses suggestion... not sure
if he was right or wrong.)why would this only happne on this particular day.
It was a rather pleasant summer day. the airplane was in the
hangar. the electricity was turned on, and the airplane was plugged
into the wall of the hangar... or to a service cart, not sure
which. there was a portable air conditioning unit outside the
airplane with a long duct running up to the door of the plane to
keep me cool.I have shot similar airplanes in similar conditions, with the Air
conditioning set up.... and never experienced these red blue and
green dots before.anyone have an idea what caused them so I can avoid them in the
future. I had to do a lot of cloning to get rid of them all.thanks
Christopher
-- hide signature --
Outside of a dog, a book is a man's best friend. Inside of a dog, it's too dark to read...
800 iso is high it is maybe noise.
You didn't tell which type of camera you used
nor if the picture that you took after were with the same parameters.
I would suggest that it comes from detector noise. You should try to avoid such high iso.
I had experience such bright pixels with my digicam under low light. without nothing special around.
Regards
Laurent
Re: 800 iso is high it is maybe noise.
It's most likely noise/errors introduced by radiation.
As you said they are taken from inside an airplane, and as a crude rule of thumb, a transatlantic flight can equal a full chest x-rax.
A friend of mine used a DV-camera connected to a pc with some sw to try to detect all kinds of "events" on the night sky, to get a idea about how often things like shooting stars etc were seen.
He found varios unexplainable non-moving dot's on some of the exposures, and we couldn't find a suitable explanation.
I then suggested to let the setup run for a full night with the lens cap on, and the specs still occurred with about the same frequency.
whether it's radiation interacting with the sensor itself or radiation causing errors in the electronics "later" in the process I don't know for sure. But since it's mostly a single pixel or 2-3 adjacent pixels, most things suggest it's in the sensor itself.
Most of the spots seem to have a single color and be maxed out in intensity. But a few of them end up white or with a slight colorcast, suggesting more than one detector was struck.
Unless the plane has flown through some nuclear fallout it's unlikely the specs are caused by radiation from the plane itself.
Was the radar or radio equipment turned on or opened for service?
Parts of the electronics that feed a radar will emit x-rax's. How much depends on the type/size/shieldning of the radar.
Re: 800 iso is high it is maybe noise.
I shoot at 800 all the time and don't experience this. heck, I even shoot at 1600 and don't experience this. Fuji chips have the reputation for the least noise a high ISO. thanks anyway though.
L. Lerusse wrote:
You didn't tell which type of camera you used
nor if the picture that you took after were with the same parameters.I would suggest that it comes from detector noise. You should try
to avoid such high iso.I had experience such bright pixels with my digicam under low
light. without nothing special around.Regards
Laurent
it was in the hangar. but I did have all the instruments turned on. I don't think radar was turned on. I don't think they can turn on radar while it is in a hangar.
but Radar , and radiation, could cause this? that is possible?
what about static electricity? is that possible?
Riberholt wrote:
Unless the plane has flown through some nuclear fallout it's
unlikely the specs are caused by radiation from the plane itself.Was the radar or radio equipment turned on or opened for service?
Parts of the electronics that feed a radar will emit x-rax's. How
much depends on the type/size/shieldning of the radar.
Static electricity would have to be extremely bad to even come close to causing anything like that. You would probaly find your cam malfunctioning completely instead, not to mention being zapped by the electricity yourself.
Radiation, mainly x-ray's could produce this. Microwaves from the radar"dish" would not though. Their wavelength is much too big to hit a single detector, and would most likely also bounce off the housing.
It's the radar's transmitter tubes that can cause the x-rays, and these do not have to sit in the nose of the radar. But there can be other sources for radiation in the plane or in the hangar. X-ray equip is used for some maintenance inspections also.
Basicly I wouldn't worry too much about it, but if you experience it again you might try asking them to turn as much of the electronics off as possible.
Did you happen to take any shots in the hangar, but not inside the plane it self?
I shot in the nosewheel, and the dots are there too. when i shot the plane outside the hangar there were no dots.
when I shot the plane outside I had the ASA set at 400. when I shot the nosewheel inside the hangar at 800asa, I think the electronics were turned off. but perhaps not. but I saw a few green and red dots. but not as many. when I shot the airplane, up close, outside a didn't see any green dots, except for one photograph by th engine that was in th shade and dark and I had set the camera at 800 quite possibly. I didn't check all the files. but I shot a close up of the landing gear at 800asa and it was totally clean.
Riberholt wrote:
Static electricity would have to be extremely bad to even come
close to causing anything like that. You would probaly find your
cam malfunctioning completely instead, not to mention being zapped
by the electricity yourself.Radiation, mainly x-ray's could produce this. Microwaves from the
radar"dish" would not though. Their wavelength is much too big to
hit a single detector, and would most likely also bounce off the
housing.It's the radar's transmitter tubes that can cause the x-rays, and
these do not have to sit in the nose of the radar. But there can be
other sources for radiation in the plane or in the hangar. X-ray
equip is used for some maintenance inspections also.Basicly I wouldn't worry too much about it, but if you experience
it again you might try asking them to turn as much of the
electronics off as possible.Did you happen to take any shots in the hangar, but not inside the
plane it self?
hurstdog • New Member • Posts: 13
Re: why are there red, blue, green dots in my photos?
Christopher Mann wrote:
...
...
does anyone know what could have possibly caused these dots to appear?
How long were the exposures? Were you shooting a lot in a short period of time when these appeared?
I think that most likely they are hot pixels. I get them when I take shots of stars with my D70, if I turn on long exposure noise reduction they go away though.
Its not x-rays, or other type of radiation, its blown channels caused by pixels overheating. They're red, green, and blue because thats the colors the blown pixels pick up.
For more info: http://www.imaging-resource.com/ARTS/HOT/HOT.HTM
Its something that every digital camera does to some degree, especially with longer exposures and higher ISO's.
Here are two shots that demonstrate what in-camera noise reduction can do, both taken from Lake Tahoe about a month ago, both over a minute exposure with ISO 800+.
First, with no noise reduction, you might have to zoom in to see the red, green, and blue pixels. Also, you'll notice a purple cloud in the top right, because of the heat generated from the camera's internal circuitry exposing the image.
With Long-Exposure NR turned on, it takes a dark frame of the same length as the frame it just took, and subtracts it from the previous frame to get rid of the noise. Here are the results (note that this was taken from a different perspective, and about an hour after the first shot):
Both of those should be a little blurry, I was still getting the hang of manual focusing on the stars in those shots.
Hope that helps.
-Andrew
Re: why are there red, blue, green dots in my photos?
Glitter perhaps? Or small specks of machined metal?
I took a picture once of someone's jacket and got something much like that from it, random very high intensity specks of color from it. Turns out she'd used glitter makeup a day or two before. Maybe your specks were just something tiny and reflective. Photoshop's auto-levels has been known to exagerate lighting defects.
cilles • Forum Member • Posts: 88
Re: why are there red, blue, green dots in my photos?
How about reflections off of the glass of the cockpit or other lights inside the cabin? They may have been small or dim to the naked eye.
-Chris
Re: why are there red, blue, green dots in my photos?
If they do only show up inside the plane, not before, not after, then it's fairly probable that the problem lies within the airplanes environment.
Was your camera by chance hotter than usual when you took the photo's inside the plane?
I know you said AC was on inside the plane, but if the cam had just come from a hot environment, like a car or being exposed to direct sunligt, this higher temperature could amplify the problem of hot pixels, causing them to appear more prominent than usual.
Noise roughly doubles for every 6-8 degrees C the temp rises, so a cam at 35+ C would seem much noisier than the same cam at 20 C. This way luke warm pixels could turn hot if the exposures are long.
Reflections from the light in the cockpit would not show up as just these small specs, rather as a nice blend of big and small reflections. Not to mention the cockpit windows that would be clearly visible.
(Sun)light hitting dust specs etc could be a possibility, but would also be evident to the person taking the pictures.
Are the pixels always in the same positions?
if they are it's 99% sure it's hot pixels, if not i woudn't rule out ionizing radiation caused them
Re: why are there red, blue, green dots in my photos?
Hurstdog, of all the answers I have recieved, yours is the only one I believe makes sense. I didn't know about "hot pixels". it was pretty hot in the plane. the exposures were merely one second. but I think your answer fits. I really do. thank you very much.
hurstdog wrote:
Christopher Mann wrote:
...
...
does anyone know what could have possibly caused these dots to appear?How long were the exposures? Were you shooting a lot in a short
period of time when these appeared?I think that most likely they are hot pixels. I get them when I
take shots of stars with my D70, if I turn on long exposure noise
reduction they go away though.Its not x-rays, or other type of radiation, its blown channels
caused by pixels overheating. They're red, green, and blue because
thats the colors the blown pixels pick up.For more info: http://www.imaging-resource.com/ARTS/HOT/HOT.HTM
Its something that every digital camera does to some degree,
especially with longer exposures and higher ISO's.Here are two shots that demonstrate what in-camera noise reduction
can do, both taken from Lake Tahoe about a month ago, both over a
minute exposure with ISO 800+.First, with no noise reduction, you might have to zoom in to see
the red, green, and blue pixels. Also, you'll notice a purple
cloud in the top right, because of the heat generated from the
camera's internal circuitry exposing the image.
With Long-Exposure NR turned on, it takes a dark frame of the same
length as the frame it just took, and subtracts it from the
previous frame to get rid of the noise. Here are the results (note
that this was taken from a different perspective, and about an hour
after the first shot):
Both of those should be a little blurry, I was still getting the
hang of manual focusing on the stars in those shots.Hope that helps.
-Andrew
hurstdog • New Member • Posts: 13
Re: why are there red, blue, green dots in my photos?
Christopher Mann wrote:
Hurstdog, of all the answers I have recieved, yours is the only one
I believe makes sense. I didn't know about "hot pixels". it was
pretty hot in the plane. the exposures were merely one second.
I don't think that the temperature in the plane had as much to do with it as the length of the exposures. As I understand it the CCD heats up quickly with extended use, and you taking many 1 second exposures in a short period of time was probably enough to do it.
Depending on what camera you have, you should be able to have it fix this automatically with a menu option, its called "Long Exposure NR" in my D70. If not, there are programs (Noise Ninja? Haven't used it, but it might work) that you can load a dark frame into, and it will be able to subtract the hot pixels for you.
but
I think your answer fits. I really do. thank you very much.
You're welcome. Glad I could help.
-Andrew
Re: why are there red, blue, green dots in my photos?
well, that makes even more sense now. I was shooting a VR inside the airplane. there were 10 positions on the rotater, and I had auto bracket. so I was shooting 30 1 second exposures in a few minutes, then another 30 exposures at another color temperature reading. I think if I buy more card space and start shooting in RAW, I won't have to bracket either the exposures OR the color temperature and I can avoid getting my pixels in my CCD so HOT.
does CMOS chips have the same problem?
Chris
hurstdog wrote:
Christopher Mann wrote:
Hurstdog, of all the answers I have recieved, yours is the only one
I believe makes sense. I didn't know about "hot pixels". it was
pretty hot in the plane. the exposures were merely one second.I don't think that the temperature in the plane had as much to do
with it as the length of the exposures. As I understand it the CCD
heats up quickly with extended use, and you taking many 1 second
exposures in a short period of time was probably enough to do it.Depending on what camera you have, you should be able to have it
fix this automatically with a menu option, its called "Long
Exposure NR" in my D70. If not, there are programs (Noise Ninja?
Haven't used it, but it might work) that you can load a dark frame
into, and it will be able to subtract the hot pixels for you.but
I think your answer fits. I really do. thank you very much.You're welcome. Glad I could help.
-Andrew
hurstdog • New Member • Posts: 13
Re: why are there red, blue, green dots in my photos?
Christopher Mann wrote:
well, that makes even more sense now. I was shooting a VR inside
the airplane. there were 10 positions on the rotater, and I had
auto bracket. so I was shooting 30 1 second exposures in a few
minutes, then another 30 exposures at another color temperature
reading.
That would do it, I would expect.
does CMOS chips have the same problem?
I'm not sure if its specific to one type of chip or another, I think it affects all digital cameras. I've heard about it happening on the 300d and the d70 forums, so it would appear that both CCD and CMOS show this problem.
-Andrew
Chris
hurstdog wrote:
Christopher Mann wrote:
Hurstdog, of all the answers I have recieved, yours is the only one
I believe makes sense. I didn't know about "hot pixels". it was
pretty hot in the plane. the exposures were merely one second.I don't think that the temperature in the plane had as much to do
with it as the length of the exposures. As I understand it the CCD
heats up quickly with extended use, and you taking many 1 second
exposures in a short period of time was probably enough to do it.Depending on what camera you have, you should be able to have it
fix this automatically with a menu option, its called "Long
Exposure NR" in my D70. If not, there are programs (Noise Ninja?
Haven't used it, but it might work) that you can load a dark frame
into, and it will be able to subtract the hot pixels for you.but
I think your answer fits. I really do. thank you very much.You're welcome. Glad I could help.
-Andrew
Source: https://www.dpreview.com/forums/thread/942323