On Wed, 25 Feb 2009, Thomas Kaiser wrote:
Also an overview is often very helpful. Also trying to visualize what
might be needed in the future is helpful. All of this can be extremely
helpful. But not everyone can see or imagine every possible thing. For
example, it seems that some of the best minds in the business are stunned
when confronted with the fact that some manufacturer of cheap electronics
in Taiwan has produced a lot of mass-market cameras with the sensors
turned upside down, along with some other cameras having the same USB ID
with different sensors, which act a bit differently. Clearly, if such a
thing happened once it can happen again. So how to deal with such a
problem?
Actually, this happens and is happening!
Just step back a get an other view.
I had plenty of other views. SQ905, SQ905C, MR97310, SN9C2028, and one or
two more. And, oh yes, the GT8290 chip on which Grandtech went broke,
which was intended for mass storage still cameras but had a 32-bit CBW
instead of a 31-bit CBW (off by one error and nobody caught it).
These consumer products are manly produced for the Windoz audience.
Very true. Usually, it even says on the package that it will not work on
Mac. But since Linux is unmentionable they did not say anything about it.
So we make it work anyway.
After introduction of Win XP the consumer where told that USB device will run
out of the box in Win XP,
Not all devices. Perhaps what they really meant is now you don't need to
install two drivers if you have two Mass Storage Transparent Scsi Bulk
Transport flash drives. To that extent, it seems that they were truthful.
There are lots of proprietary devices out there for which AFAICT the
drivers are still not included in Windows. Some of these are unfinished
projects of mine, too, such as the JL2005C cameras. The big bugbear with
those is the compression algorithm. It is a horror.
which is sometimes true, but .....
But on all (Windowz) Webcams (are Linux Webcams available?) I buy, I find a
sticker which tells me to first insert the driver CD before connecting the
cam to the PC. When you do, like instructed, your cam works like you
expected!
Of course. Hardware will not work without a driver.
Evan the USB ID is the same like the other webcam from the other vendor, you
are (more or less) forced to install the driver from this particular vendor,
you get a new driver!
Not true. Windows, even back in the days of Windows 98, searched for the
Vendor:Product number to look for the driver. There were several places to
search for the number. For example, the INF files. And I have a box full
of SQ905 cameras for which I will personally guarantee that every one of
them will work on Windows 98 with the Windows driver from the CD that came
with any other one. Now, if the picture is always facing in the right
direction, that is another question, naturally.
Doesn't matter if the sensor is mounted upside down,
the "new" driver takes care about this. So, it looks like the cam in the
Windowz World just works because you were forced to install the driver from
the CD.
And while we are on that topic, I could definitely assert that not always
did the "manufacturer" get this right, either. I, recall, developed the
original SQ905 stillcam driver for Linux. I got letters from users and
sample photos, too, where the photos came out of the camera and lettering
on a sign visible in the photo was bass ackwards. They were cheap cameras,
and the people who sold some of them were just a little bit sloppy. Their
virtue, as cheap cameras go, was comparatively good optics in some of
them. I have seen lots of cameras about the same price, which had much
more features and much worse pictures.
So I guess the Windoz diver just knows more then the USB ID.
No, not really. See above.
In the Linux World most of the drive are re-engineered, we don't know how to
detect how the sensor is mounted, do we?
Well, yes, we do. And that is what this discussion was about. How to use
that knowledge constructively while writing a kernel driver.
Actually, what I try to say, is that only the cam can know how the sensor is
mounted. Thus, the kernel module has to provide this information to user
space (by query the hardware).
Well, that is more like it. Yes, one does have to ask the camera. But the
camera will tell its answer truthfully. And this is before any streaming
and image processing has started, too. What a deal.
The "pivot" is an other thing.
Very true. And worth paying attention to. But it is not the same issue.
Thomas
Theodore Kilgore
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