Another post on noise....
Aug 15, 2013 20:40:29 #
Addendum, this is about DARK noise and how to correct it.
What is noise?
Noise is a pseudo random generation of pixels within a picture taken in low light conditions, underexposed or with a camera sensor that is exposed to significant heat, like when using 'live view' or extreme weather condition above 95F.
The generation of these 'parasite pixels' is not random but is repetitive if the exact same conditions when taking the picture can be recreated.
Noise in a JPG or any compressed file format is not recoverable without a significant loss of an image quality.
Noise in an uncompressed UNPROCESSED RAW file is possible without picture quality damages. UNPROCESSED is key here. It means that you need to plan for its presence, making sure that no image process takes place in both camera and Post Processing before working on eliminating the noise.
-------------------
Reducing noise for everyone
Planning when taking a picture
Keep camera cool (under 40c app. 90F)
Do not use live view option when shooting (a hot sensor creates more noise)
Use lower sensitivity (ISO, your normally can go up to 800)
Avoid long exposures
'Shoot to the right' (Over expose 1 to 2 f-stop, using RAW. .5 to 1 stop using JPG). There is more visible noise in the dark areas.
-------------------
Reducing noise in Post Processing (PP)
Areas are out of focus are where the type of noise can be analyzed. Always remember that noise is at the pixel level. Larger noise, called spacial frequency range can be corrected only by using the YCbCr lab model. This option works on color models that are separate from color luminosity information.
Some programs and plug-ins offer to automate noise reduction. These do so at the expense of clarity, and generate a global image quality reduction while visually pleasing.
PP correction degrades the original and results in softer edges, vibrancy is lessened, contrast is lowered, among other things.
Best option is to work on specific areas of an image areas using feathered masks and paint tools, preferably at the same time to achieve an uniform correction.
-------------------
Reducing noise for the few of us nutcases
Note that is more like a calibrating workflow than a correction one...
First off, you have to be a maniac...
For best results you need a camera that does not have a low filter like the Nikon d800e. Since the low filter influence is a constant, this is not a prerequisite, by far it just introduces a permanent set of optical errors (diffusion) to offer a 'pleasing average' and avoid moire.
Assuming the image was taken properly in an unprocessed non compressed RAW or TIFF file format.
Create a black frame reproducing the exact same conditions, including temperature of the sensor (ambient and internal, meaning if you used live view, use it again, for same length you used it when taking the original picture.
Process:
Read the image parameters used (ISO, Speed, F-stop)
Make sure the camera is set to NO IMAGE PROCESSING otherwise this will not work.
Manually set these parameters onto your camera
Prepare a black hole free trash bag (to use as a dark room)
When the camera is properly set and heated, take a picture inside the trash bag, making sure no stray light can influence your blacj frame.
Folding the trash bag in two ans pressing the shutter from outside is probably the best, plus you need a smaller bag (You do not even need a lens for this shot.
This is your correction of calibration black frame.
To avoid all this after the fact non-sense, just take the black frames on the spot, at the beginning of the shoot, the middle of it and the end. This way you have all the reference frames you will ever need and they will be more accurate than the one you create afterward. Of course this assumes that you will be using your camera on manual mode and will not fiddle with the settings... Right.
Now, using a program that uses layers:
Open both images using absolutely no image processing (dig into the raw import to uproot all default changes that are otherwise hidden ESPECIALLY sharpening in its many iterations). I cannot insist more, open both AS SHOT.
Select the calibration frame and copy the full frame using CTRL-A CTRL-C (Command-A and Command-C)
Copy the selection onto the original image as a layer CTRL-V (Command-V)
Select Blend mode and set it for 'Difference', opacity 100%
If you want to apply this only to selected area of the picture, use the now infamous mask painting feature.
Because this method is really precise you must keep the layers together and have them immediately above the background layer (or copy of it). Using CS6 or CC you can create a group layer to preserve this process. DO NOT FLATTEN the image even if you really can do it. The reason? You might want to go back and do some minute adjustments following changes you make later on.
-------------------
Some camera manufacturers (Canon among others) offer a dark frame correction option. While this work relatively well, the camera computer cannot match the sophistication of PP software and computing power.
-------------------
That's it, good luck, hunting and all that.
All corrections, grammar, spelling and factual are welcomed. This will end-up in a small book whenever I am ready to self publish.
-------------------
Sources for this article:
http://www.laesieworks.com
http://photographylife.com
http://image-sensors-world.blogspot.com
http://www.sphoto.com
http://en.wikipedia.org
http://www.lightstalking.com
http://photo.net
Now, if one of you readers could give me a tip on how to get rid of squirrels without killing them, I'll be glad to try it.
What is noise?
Noise is a pseudo random generation of pixels within a picture taken in low light conditions, underexposed or with a camera sensor that is exposed to significant heat, like when using 'live view' or extreme weather condition above 95F.
The generation of these 'parasite pixels' is not random but is repetitive if the exact same conditions when taking the picture can be recreated.
Noise in a JPG or any compressed file format is not recoverable without a significant loss of an image quality.
Noise in an uncompressed UNPROCESSED RAW file is possible without picture quality damages. UNPROCESSED is key here. It means that you need to plan for its presence, making sure that no image process takes place in both camera and Post Processing before working on eliminating the noise.
-------------------
Reducing noise for everyone
Planning when taking a picture
Keep camera cool (under 40c app. 90F)
Do not use live view option when shooting (a hot sensor creates more noise)
Use lower sensitivity (ISO, your normally can go up to 800)
Avoid long exposures
'Shoot to the right' (Over expose 1 to 2 f-stop, using RAW. .5 to 1 stop using JPG). There is more visible noise in the dark areas.
-------------------
Reducing noise in Post Processing (PP)
Areas are out of focus are where the type of noise can be analyzed. Always remember that noise is at the pixel level. Larger noise, called spacial frequency range can be corrected only by using the YCbCr lab model. This option works on color models that are separate from color luminosity information.
Some programs and plug-ins offer to automate noise reduction. These do so at the expense of clarity, and generate a global image quality reduction while visually pleasing.
PP correction degrades the original and results in softer edges, vibrancy is lessened, contrast is lowered, among other things.
Best option is to work on specific areas of an image areas using feathered masks and paint tools, preferably at the same time to achieve an uniform correction.
-------------------
Reducing noise for the few of us nutcases
Note that is more like a calibrating workflow than a correction one...
First off, you have to be a maniac...
For best results you need a camera that does not have a low filter like the Nikon d800e. Since the low filter influence is a constant, this is not a prerequisite, by far it just introduces a permanent set of optical errors (diffusion) to offer a 'pleasing average' and avoid moire.
Assuming the image was taken properly in an unprocessed non compressed RAW or TIFF file format.
Create a black frame reproducing the exact same conditions, including temperature of the sensor (ambient and internal, meaning if you used live view, use it again, for same length you used it when taking the original picture.
Process:
Read the image parameters used (ISO, Speed, F-stop)
Make sure the camera is set to NO IMAGE PROCESSING otherwise this will not work.
Manually set these parameters onto your camera
Prepare a black hole free trash bag (to use as a dark room)
When the camera is properly set and heated, take a picture inside the trash bag, making sure no stray light can influence your blacj frame.
Folding the trash bag in two ans pressing the shutter from outside is probably the best, plus you need a smaller bag (You do not even need a lens for this shot.
This is your correction of calibration black frame.
To avoid all this after the fact non-sense, just take the black frames on the spot, at the beginning of the shoot, the middle of it and the end. This way you have all the reference frames you will ever need and they will be more accurate than the one you create afterward. Of course this assumes that you will be using your camera on manual mode and will not fiddle with the settings... Right.
Now, using a program that uses layers:
Open both images using absolutely no image processing (dig into the raw import to uproot all default changes that are otherwise hidden ESPECIALLY sharpening in its many iterations). I cannot insist more, open both AS SHOT.
Select the calibration frame and copy the full frame using CTRL-A CTRL-C (Command-A and Command-C)
Copy the selection onto the original image as a layer CTRL-V (Command-V)
Select Blend mode and set it for 'Difference', opacity 100%
If you want to apply this only to selected area of the picture, use the now infamous mask painting feature.
Because this method is really precise you must keep the layers together and have them immediately above the background layer (or copy of it). Using CS6 or CC you can create a group layer to preserve this process. DO NOT FLATTEN the image even if you really can do it. The reason? You might want to go back and do some minute adjustments following changes you make later on.
-------------------
Some camera manufacturers (Canon among others) offer a dark frame correction option. While this work relatively well, the camera computer cannot match the sophistication of PP software and computing power.
-------------------
That's it, good luck, hunting and all that.
All corrections, grammar, spelling and factual are welcomed. This will end-up in a small book whenever I am ready to self publish.
-------------------
Sources for this article:
http://www.laesieworks.com
http://photographylife.com
http://image-sensors-world.blogspot.com
http://www.sphoto.com
http://en.wikipedia.org
http://www.lightstalking.com
http://photo.net
Now, if one of you readers could give me a tip on how to get rid of squirrels without killing them, I'll be glad to try it.
Aug 15, 2013 22:18:12 #
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