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Originally Posted by tsk1979 Since I have taken shots with 350D ranging from few seconds to 30 minutes(without dark frame noise substraction) I have observed differently. For shorter exposures, there are no "hot pixels", but for longer exposures they are. |
That is Called ADC error. Hot pixels are Calibrated till ADC error comes on and Hot pixels are displayed.
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Originally Posted by tsk1979 You are confusing Hot Pixels with Stuck/Dead pixels. |
No I am not.
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Originally Posted by tsk1979 |
If you cared to read the link, it clearly indicated about and CCD/CMOS sensors (i even quoted it for your ease). Not only that but the link also pointed to ISO standards for Visual and Imaging standards which clearly indicated different types of faults in pixels in terms of CCD/CMOS and LCD.
BTW for everyone, doesn't matter where one check out, there is no
STANDARD for pixels in Imaging Sensors. Closest one can find is CCD sensors implementation for back current in Laser diodes (optical pickup assemblies). Assumed similarity is taken into account from above link. Please check with NPS, CPS, ISO, IEEE, ITC and ISE.
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Originally Posted by tsk1979 Last but not the least, the pic you posted does not look like a Hot Pixel at all. Looks more like an artifact or stuck pixel. Here is a 100% crop showing a "hot Pixel" Attachment 276958
Now coming to your point of defective pixels, they are stuck pixels.
A stuck pixel will appear in all the shots. A hot pixel will appear only on the Longer exposures.
Take a 10 minute exposure in a dark room with lens cap on. then wait some time, and take a 10 second exposure with lens cap on in a dark room.
In the 10 minute exposure you will see a lot more hot pixels.
However, if your camera has dead pixels, they will show up in all the shots.
For the record, I did a test on my camera, and there were 2 or 3 "Stuck pixels" on my camera(a very very insignificantly small percentage of the 8 MP)
There are lots of web programs which can analyze the image from your cam, and tell you the exact number of Dead/Stuck and Hot pixels.
So By definition
Stuck pixel = a pixel that always reads high (maximum) on all exposures.
Hot pixel = a pixel that reads high on longer exposures.
Dead pixel = a pixel that reads zero (black) on all exposures.
A stuck pixel or a dead pixel is a defective pixel, but a hot pixel is not a defective pixel, and will show up only on very long exposures.
Typically many cams have 1 or 2 hot pixels at 30 seconds exposure, and as the exposure time increases, more and more pixels go hot.
Compact cams have a lot more than larger sensors. |
The picture I included consists of HOT Pixel, once you read the link posted by me, it will make it clear. And the reason I selected actual world image above is because I have seen the picture and the camera myself. On top the image was taken at low shutter speed with bright light. Airplane was in flight, that is why its not blurred.
The image and the Definitions your have shown are from Bryan's WebPages, which are at least 7yrs old and information is not current. Even if you choose to accept the information provided by Byran, this is the person who is not able to adjust while balance both on camera and post processing. Do you want me to explain more about him and his experiments ???
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Originally Posted by tsk1979 So if I get a hot pixel, after that it will show in all the pictures at all shutter speeds? Well here is a long exposure I took long time back. This is equivalent of over an hour of exposure. Hot pixels have been circled. There are many because I did not take dark frame substraction, and ambient temp was very high. For actual exact image please look at link at the end of this post Attachment 276972
Now according to what you said, in all my subsequent shots, I should be seeing these "hot pixels"?
Well I do not
Since the JPEG compression on the site is killing the quality, here is the link to image on smugmug where you can see it more clearly http://tanveer.smugmug.com/Travel/Hi...3_ApvjF-XL.jpg |
Looks more like ADC errors to me than Hot Pixels.
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Originally Posted by Rudra Sen Why one would shoot with white balance off? I don’t get the reason! Is there any special advantage? If yes then I would like to know what is that. I haven’t shot anything till date without white balance on and it is at AUTO setting from the day one. I don’t think I’ve lost any or got any wrong colour information. |
My intended meaning was for shooting with White Balance Off as Uncalibrated Colours. DSLR manufacturers put only
REAL Calibration in the body for us to use and take benefit of. Sadly majority of the users ignore it. If you havn't used it then you are not taking full advantage of your hard earned cash.
Like I said earlier, in the end its upto the user to either trust a proper color calibration tool which costs nothing vs uncalibrated LCD.
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Originally Posted by Rudra Sen Subjective statement. What is optimum is a question as always. You see something before shooting and want it to reproduce faithfully is something can be close to optimum. Or that’s what I believe. Can I enhance that? Sure I can if I have all the information in my RAW file. Do I need to do that? Yes and no. It depends greatly on final application. |
Well yes its a subjective statement. If i have to show that there is car parked with XYZ number plate in the driveway, well colors dont matter since the main information is there. While if its a Wallpaper or a picture going for printing so i can put it on the wall or a picture for a client, well
AT-LEAST one kind of calibration should be there.
And since normal users cannot afford LCD - Printer calibration units, Custom White Balance suddenly becomes quite an important feature. I would honestly like to know how many users here Own LCD/Printer Calibration unit.
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Originally Posted by Rudra Sen Do not buy this at all. If that’s the case then one should be seeing those defective pixels right through all images. That doesn’t happen. |
Well I would not bother with providing links or anything or typing extra information. Just the information provided by Tanveer was taken from Byran's WebPages and he said same thing just like you. Nikon still replaced his cameras sensor under warranty. Even Nikon’s own Support page suggests bring in DSLR when Hot Pixels are evident so it can be tested and repaired if necessary. One thing they do not mention is whether Errors from ADC will be replaced or not and if Hot pixels are found whether Nikon will replace the sensor or just re-map it.
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Originally Posted by Rudra Sen Where? On the same place? If I may ask you from where are you getting all these information? Three shots below were taken within a span of hour and half. I’ve marked the areas where hot pixels were sitting. All three were with roughly 30 seconds+- time. |
Yes Hot pixels appear on the same place.
I get my information from NPS, CPS, ISO publications, IEEE publications, ISE and Current research papers at different universities (yes i got the time, since i am not even allowed to leave my bed for next few months).
Did you bothered to notice that all of the supposed hot pixels in your pictures are in
DARK SPOTS.
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Originally Posted by Rudra Sen Really? Then how come I don’t see them all the time? Sample as what you have put up is not hot pixel at all. What I see from TSK is more like it. |
You should read on ADC errors then.
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Originally Posted by Rudra Sen Oh! Then how come I didn’t find any hot pixel on any of my May ’07 shooting at UP? I was shooting at 45 degree. |
What I wrote was:-
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Noise starts increasing as sensor gets hot and fades away as sensor cools down. Hot Pixel will stay all the time.
|
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Originally Posted by Rudra Sen What concert photographers do is not important unless that is somebody’s bread and butter. Let us be real here. I’ve seen hot pixels from Nikon’s top of the line cameras. That doesn’t say anything. Similarly I’ve seen excellent result from 6000/- point and shoot camera. |
Quite the opposite, What Concert photographers do is actually very important, that is if one understands what they are doing.
I am being real. Can you point out other
REAL COLOR CALIBRATION any members here can perform in
REAL LIFE without buying units like Colormunki/Spyder3. I only put up the example and experiment in
HOPE to teach members to get
FREE CALIBRATION which otherwise they cannot afford. Maybe I was wrong to think to help others.
Here is an example of what Custom White Balance can do. Poth pictures straight from the camera, no PP except Cropping and resizing.
This Picture was taken with Custom White Balance.
This Picture was taken at the same concert but without Custom White Balance.
Maybe I am an Idiot to think members here will benefit from it.
I didn't knew i said anything about highend cameras. I quite agree with you, someone with creative mind can right technique can produce better results with a Holga than someone with no creative mind and using H3D.
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Originally Posted by Rudra Sen it_inspector. My humble request to you: Be real. Searching internet for all the solutions and beating around the bush is the same in the sphere of digital photography. If there are white pixels/dead pixels/hot pixels.. Too bad. One must know how to work around that. And if you know that then please guide us. |
Actually searching internet is dependent on the user. There is both garbage and gold on the internet. Use Google and one gets garbage first and by the time user reaches to gold, he/she is already too overwhelmed and cannot digest any gold.
I like to help and currently work with teenagers from different schools who want to join photography both as a hobby and as profession. To see some of the things i have done, Please search for “The Big Issue Homeless World Cup Melbourne 2009” in Flickr. This was the first time a group of Amateurs were allowed to go where Pros go and shoot. Pros were kicked out and only these guys were allowed to shoot. Anyone with keen eyes should be able to find few shots which have been circling publications of a goalkeeper who is stopping a goal but being photographed by Amateurs from more than 4 different angles at the same time and no this was not planned, whole point was to let a group of amateurs go wild with their kits and it was a blast for them.
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Originally Posted by Rudra Sen I’m sorry if I’m sounding rude here. It’s not my usual self and trust me on this. I’m flabbergasted with your series of replies.
There are many members here interested in photography. Some of them are advanced and some of them are just getting in. Your wealth of knowledge should be guiding them and not the other way round. |
No, you’re not sounding rude. Everyone gets flabbergasted when non-traditional information is dumped on them

and it could be my fault, since i dont give information like I am feeding someone. I expect others to earn it by going through the links and experiments i post.
When everyone started converting from FILM to Digital, scenario was a mess. Those who were engineers with experience knew the actual issues at hand but were no photographers. Photographers who were facing the issues didn't know what was happening. As a result penetrating Professional market was harder and took some time and Myth's started to emerge and wrong information started to spread faster than Wild Fire, Users were the ones who got burnt in this fire while for manufacturers it was god sent, cover up the issues and defects and users will never know.
And the sad fact is, no one knew any better and it worked. It worked so good that there is no
REAL International Standards for Camera and Imaging Sensors till this day. Only actual world Standards for Sensors at the moment are derived from "Sensors and Actuators standards" at IEEE and "Visual Display Standards" at ISO. None of which actually help standardise DSLR's but helps Manufacturers cover defects with things like Dark Frame Subtraction.
To understand current situation and why ISE is constantly being shunned down and not allowed to print even a single publishing openly, one needs to read the basics.
If anyone bothers to Read APS thesis by Glenn H. Chappman, they will understand the actual Hot Pixels and ADC errors in detail. Also it greatly talks about OLDIA which is the secret behind Nikon D3s. Since it doesn't deal with noise but with Hardware and Software to correct "Active Pixel Sensors". I promise this will change your thinking on the topic of DSLR's forever, all one needs to do is to find it and read it.
But anyhow here's the comment by him on Hot Pixels:
"Because the definition of a hot pixel is typically application dependant, a hot pixel was taken to be any defect in which the dark signal would noticeably degrade image quality under typical usage conditions for these cameras:
any pixel that reached 25% of maximum value in 1 second under no illumination at ISO 400 sensitivity."
PS: Here "these" refers to
SOLID STATE SENSORS. This was Also accepted by IEEE and ISO, although ISO has not issued a publication yet and ISE cannot accept anything till other 150+ members let it.
Since I know no one will bother to actually go find it and read it, I will point to ISO 13406-2 which is Industry wide standard (or lack thereof) for any default related to Pixels whether it’s a Display panel or a Imaging Sensor.
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The standard lists four classes of devices, where a device of a specified class may contain a certain maximum number of defective pixels. Three distinct
types of defective pixels are described:
type 1 = a hot pixel (always on, being colour white)
type 2 = a dead pixel (always off, meaning black)
type 3 = a stuck pixel (one or more sub-pixels (red, blue or green) are always on or always off)
The table below shows the maximum number of allowed defects (per type) per 1 million pixels.
Definition of Pixel Fault Classes – Maximum number of faults per million pixels
Class Type 1 Type 2 Type 3 Cluster with more than one type 1 or type 2 faults Cluster of type 3 faults
I 0 0 0 0 0
II 2 2 5 0 2
III 5 15 50 0 5
IV 50 150 500 5 50
As of 2007, most manufacturers specify their products as Pixel Fault Class II |
Now if I still have to explain on supposed Hot pixels in above posted images. Well these are called
Analog-to-Digital-Convertor (ADC) errors. ADC errors are more common than Hot pixels and are affected by leaking currents the most. There is nothing known as a DIGITAL sensor, sensors still work in analog mode and each sensor as a ADC behind it (excluding backlit sensors) to convert Analog signals to Digital. ADC's fail after constant use of 1s or over. Hence, for proper HOT PIXEL test 1s is the maximum limit used by manufacturers (if I am correct ISE has this covered in 2010 agenda and new standards are supposed to be purposed in ISE2010).
Error due to failure of ADC are also mapped out at factory since it is too expensive to produce sensors without errors and one of the major reason why anything less than 1.5x crop attracts more money. During dark frame subtraction, mapping is also applied to hide ADC errors and is quite effective.
In order to confirm it, all one needs to do is to perform Dark Frame Subtraction manually in Photoshop.
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Originally Posted by clevermax I am not an expert in this field, many of us are not. So it’s natural that many of us folks fail to distinguish between bullsh***ing and real expert talk and some seem to take advantage of this. But if one tries to learn things on his/her own and try to interpret what seems to be OHT talk (Over head transmission) we can all really understand what is real and what is not. |
In the end it’s your decision to get conned or open your eyes and understand the situation. And the bad thing about both OTH and SEX are not when you take out the taboo and try to understand them.
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Originally Posted by shajufx Clever, there is an auto image cleaning process that happen every time I turn it ON and OFF, but that didn’t help much. I went through the Menu and did the shutter lock-up for a manual cleaning. 'Lifting' means manually lifting the mirror inside, not the sensor. I think I have to try some blower thing for a safer cleaning than doing with objects that can worsen the situation. |
Sensor cleaning is done by Ultrasonic vibrations on a slim filter in front of the sensor. It works perfectly fine for dry dust but anything with moisture and it fails. For proper cleaning, I use Cooper's Hill method or PEC pads. But both are a bit expensive.
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Originally Posted by navin 1. I suspect Ken Rockwell's self deregatory comments are just so that the public does not call him cocky.
2. Are you sure about the Hot pixels. I believe I have seen the disappear and re-appear on a few occasions. Still I wont pit my photography knolwedge against yours. Besides I was not looking for hot pixels (when I noticed that there were hot pixels in some pictures) I was looking at the subject. |
1. Even the persons who know Mr.Kenrockwell personally make it clear that's he is not cocky.
2. If I am not sure then I should burn my DMC's from RMIT. Hot Pixels cannot be displayed in viewfinder, they show during post processing.
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Originally Posted by shajufx I dont know how to explain the technical parts here, but when I do the mirror lock up for cleaning, it lifts and I can clean the area. But when I lift it manually, I find a twin layer on the mirror itself, which never opens by 'lock-up' process. So I lifted the mirror and tried cleaning between the twin layer manually. Anyway I dont think its some dust inside there, but could be in or around the mirror itself. Need to check some test snaps again and see if it has improved. This issue was not seen in the pics shot 7 days back. |
What you are experiencing by lifting mirror is different. Reflex Mirror (Its not a Pentamirror, Pentamirror is a cheap alternative to Pentaprism or technically known as "Roof Pentaprism") used in DSLR’s is polished with silver coating, using a Q-tip/Ear bud can damage it very badly. Mirror is actually a beam splitter in the middle where light beam is split between 2 beams. First beam goes towards the Focusing screen and is eventually seen through viewfinder. Second beam goes through the mirror and affects Secondary (AF mirror) mirror which is perpendicular to the back of First mirror. This beam is focused on AF sensor.
This is needed to perform Phase Detection AF, since Phase Detection also needs both FRONT and BACK focus to perform Accurate AF. Majority of the Film shooters fail to understand that Phase Detection is basically a Simple Rangefinder.
I suggest using a Blower or a compressor with Moisture trap and keep it at around 50psi. Also remember, never vaccum the Sensor box, Sucking air at high speeds introduces ionization.
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Originally Posted by govigov @entire team, Thank you all for the response, did not want to post in between all the confusion. picked up the eos 1000D the IS lens. loving it. still waiting for the filters to arrive. they shall arrive only by tuesday at the canon dealership. i am looking for the RS60-E3 remote switch. almost all website/canon dealerships has this out of stock. will post some pics taken using the cam soon. |
Try Dealextreme for accessories than ebay or Canon dealers. You will be happy. Only issue, Dealextreme is a bit slow with shipping.
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Originally Posted by ph03n!x A n00b question- have started shooting JPG+RAW (JPG for convenience sake, RAW... ...I hope to learn PS and PP them sometime  ). Which is the best way to edit RAW - using the PS plugin for opening RAW? Or by processing it through DPP? If I process it in DPP, do I save the RAW file itself (as a copy), or convert to TIFF and then open it in PS? |
Get yourself a copy of Light Room and use it both to view RAW files and to catalogue your shots. This might be the best accessory you can get for your DSLR.
Cheers