(Effective) pixels?

When a camera is advertised as having, say, 5 MP (effective), what does it
mean for them to be (effective), and why is (effective) in parentheses?


--
"When the fool walks through the street, in his lack of understanding he
calls everything foolish." -- Ecclesiastes 10:3, New American Bible

That would be how many pixels are in the final image. The sensor has more
pixels that this. Most sensors have some pixels that are optically shielded
(under the metal frame) that are used to measure the dark current for that
row for correcting the black level. There may be some that are partially
lit from being very close to the frame. These are also cropped off as they
have imaging problems. Finally the sensor may have a few more imaging
pixels than are used if the aspect ratio is not exactly what the
manufacturer wanted or for use in "de-bayerizing" the edges. These might be
cropped out also to produce the image size that they wanted and not have
colour distortions at the edge of the picture if they want to use an
algorithm that doesn't handle edges correctly.

All of this adds up to an image that has fewer pixels than the sensor. You
are probably not missing more than a couple of hundred thousand pixels
compared to the full sensor array count. If your image included everything,
there would be a border around the edge that starts with soft focus (from
the frame edge and diffraction), the progresses into a light band (but no
image), fading to black at the outside edges. So they crop off the bad
parts and give you the effective size so you don't wonder why your 5.2 mp
sensor only gives 5.0 mp images.



"Gregory L. Hansen" wrote in message
...

When a camera is advertised as having, say, 5 MP (effective), what does it
mean for them to be (effective), and why is (effective) in parentheses?


--
"When the fool walks through the street, in his lack of understanding he
calls everything foolish." -- Ecclesiastes 10:3, New American Bible

In article _XCnf.103982$Gd6.59104@pd7tw3no,
default wrote:
That would be how many pixels are in the final image. The sensor has more
pixels that this. Most sensors have some pixels that are optically shielded

The sensor has *more* pixels? Good for technology! I had assumed that
(effective) pixels was marketing speak for fewer pixels on the sensor but
making it up somehow in the image.


(under the metal frame) that are used to measure the dark current for that
row for correcting the black level. There may be some that are partially
lit from being very close to the frame. These are also cropped off as they
have imaging problems. Finally the sensor may have a few more imaging
pixels than are used if the aspect ratio is not exactly what the
manufacturer wanted or for use in "de-bayerizing" the edges. These might be
cropped out also to produce the image size that they wanted and not have
colour distortions at the edge of the picture if they want to use an
algorithm that doesn't handle edges correctly.

All of this adds up to an image that has fewer pixels than the sensor. You
are probably not missing more than a couple of hundred thousand pixels
compared to the full sensor array count. If your image included everything,
there would be a border around the edge that starts with soft focus (from
the frame edge and diffraction), the progresses into a light band (but no
image), fading to black at the outside edges. So they crop off the bad
parts and give you the effective size so you don't wonder why your 5.2 mp
sensor only gives 5.0 mp images.



"Gregory L. Hansen" wrote in message
...

When a camera is advertised as having, say, 5 MP (effective), what does it
mean for them to be (effective), and why is (effective) in parentheses?


--
"When the fool walks through the street, in his lack of understanding he
calls everything foolish." -- Ecclesiastes 10:3, New American Bible




--
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in-boxes, but they fear a proposed national 'Do Not Spam' registry will
make it impossible to use e-mail as a marketing tool."
http://www.bizjournals.com/houston/s...wscolumn6.html

"Gregory L. Hansen" wrote in message
...
In article _XCnf.103982$Gd6.59104@pd7tw3no,
default wrote:
That would be how many pixels are in the final image. The sensor has more
pixels that this. Most sensors have some pixels that are optically
shielded

The sensor has *more* pixels? Good for technology! I had assumed that
(effective) pixels was marketing speak for fewer pixels on the sensor but
making it up somehow in the image.

It is marketing speak in some cases. A prime example is the Bell & Howell
camera ads seen in some magazines. Those extra pixels are interpolated.

In article ,
Charles Schuler wrote:

"Gregory L. Hansen" wrote in message
...
In article _XCnf.103982$Gd6.59104@pd7tw3no,
default wrote:
That would be how many pixels are in the final image. The sensor has more
pixels that this. Most sensors have some pixels that are optically
shielded

The sensor has *more* pixels? Good for technology! I had assumed that
(effective) pixels was marketing speak for fewer pixels on the sensor but
making it up somehow in the image.

It is marketing speak in some cases. A prime example is the Bell & Howell
camera ads seen in some magazines. Those extra pixels are interpolated.

Darn, I was hoping for a simple answer.

What about Canon's new camera with the full-frame sensor for $3000? That
seems like too high a price tag for stupid marketing speak.


--
"The hardest conviction to get into the mind of the beginner is that the
education he is receiving in college is not a medical course but a life
course for which the work of a few years under teachers is but a
preparation." -- Sir William Osler

"Gregory L. Hansen" wrote in message
...
In article ,
Charles Schuler wrote:

"Gregory L. Hansen" wrote in message
...
In article _XCnf.103982$Gd6.59104@pd7tw3no,
default wrote:
That would be how many pixels are in the final image. The sensor has
more
pixels that this. Most sensors have some pixels that are optically
shielded

The sensor has *more* pixels? Good for technology! I had assumed that
(effective) pixels was marketing speak for fewer pixels on the sensor
but
making it up somehow in the image.

It is marketing speak in some cases. A prime example is the Bell & Howell
camera ads seen in some magazines. Those extra pixels are interpolated.

Darn, I was hoping for a simple answer.

What about Canon's new camera with the full-frame sensor for $3000? That
seems like too high a price tag for stupid marketing speak.



That isn't marketing speak, it is a full 12.8mp, 35mm sized (24mmx26mm
approx) sensor.

--
Skip Middleton
http://www.shadowcatcherimagery.com

"Gregory L. Hansen" wrote in message
...

When a camera is advertised as having, say, 5 MP (effective), what does it
mean for them to be (effective), and why is (effective) in parentheses?


--
"When the fool walks through the street, in his lack of understanding he
calls everything foolish." -- Ecclesiastes 10:3, New American Bible

Each photosite (sensor) on a Bayer sensor determines what color it's
supposed to be from the surrounding sensors. For instance, if the red
sensor detects it's fully activated and the surrounding blue and green
sensors are too, then the red one knows it's supposed to be white. If the
blue ones are inactive (only red and green active), then it knows it should
be yellow...and so on.
Well, the photosites around the perimeter of the whole sensor don't have
surrounding pixels from which to determine their color. They have to be
discarded because of that. They're only used so that the inner pixels can
determine their color. So, for a sensor, say, 2400 x 3600 there's 12,000
photosites that don't contribute to the final image.

(Gregory L. Hansen) writes:

The sensor has *more* pixels? Good for technology! I had assumed that
(effective) pixels was marketing speak for fewer pixels on the sensor but
making it up somehow in the image.

In the early days of digital cameras, manufacturers sometimes quoted the
total number of pixels fabricated on the sensor, including ones that did
not appear in the final output image (for whatever reason). So you
would get an image with 1.2 million pixels from a "1.3 megapixel"
camera.

Then someone established the standard that "effective pixels" are ones
that actually contribute to the image. So, for most cameras, the number
of effective pixels is a fair way to compare them.

Dave

Effective, means "We're lying."

--
http://www.chapelhillnoir.com
home of The Camera-ist's Manifesto
The Improved Links Pages are at
http://www.chapelhillnoir.com/links/mlinks00.html
A sample chapter from "Haight-Ashbury" is at
http://www.chapelhillnoir.com/writ/hait/hatitl.html

"Gregory L. Hansen" wrote in message
...

When a camera is advertised as having, say, 5 MP (effective), what does it
mean for them to be (effective), and why is (effective) in parentheses?


--
"When the fool walks through the street, in his lack of understanding he
calls everything foolish." -- Ecclesiastes 10:3, New American Bible

Fuji has been known to do that, too.