Dieter wrote:
If it is anything like PDF I want nothing to do with it.
PostScript is good, but PDF is an unending source of problems.
:-(
Only the future can tell if there will be issues like with PDF.
However, PDF is a standard and there is a lot of non-Adobe software
that uses it.
and displays incorrect images, crashes, etc.
I haven't really had any problems with it. Like all new software, XPDF
didn't render PDF perfectly to start with. AFAIK, GhostScript renders
PDF 100% OK. Although I have found PS files that it wouldn't distill.
This would be expected since PDF is based on PostScript.
IIUC, with DNG, the actual image is saved with an existing image standard.
For still images what about png?
Would that be better or worse than lossless JP2K?
I know nothing about JP2K. IIRC png is supposedly lossless and seems
to have decent compression. Xv and at least some web browsers can
do png.
First note that PNG was not designed to compress photographs so it
produces a fairly large file size when used on a photograph. It will be
larger than a 100% JPEG (which isn't really 100% -- there is some loss)
file and much larger than the typical 85% JPEG file. An 75% JP2 looks
much better than an 85% JPG and it is about the same size mainly because
the of the lack of artifacts.
http://www.oreillynet.com/pub/a/javascript/2003/11/14/digphoto_ckbk.html
IIUC, JP2 gives better quality for lossy compression at a given
compression ratio. A major advantage is that it doesn't compress in
blocks so doesn't have the blocks like JPG has. And, lossless JPEG
2000, the JPF file format, can be used to store the image in a RAW file.
The only problem is that it is slower than regular JPEG. The
computations are faster but there are more of them since it does the
image pixel by pixel rather than in blocks.
And then there is JPC (Japan Picture). This seems to be a JP2 derivative.
<SNIP>
How do you change the sensitivity of the sensor? I'd think it
was fixed. As far as I can tell my camera doesn't allow changing
the sensitivity.
That is what happens when you set the ISO on the camera.
I would think that the sensitivity of the sensor would be constant.
But then I know close to nothing about the sensors. Is there some
bias Voltage (or something) that changes the sensitivity?
The saturation sensitivity of the sensor is constant (the White level)
-- a given parameter of the sensor which is why you can't reduce the ISO
setting beyond a certain value (but why don't they make less sensitive
sensors?). However, since there is no Black level (it goes to minus
infinity) you can amplify the output to increase the ISO limited only by
the noise. So you have the base ISO for the chip times the factor used
to get the white in the scene to white in the ADC output and that gives
you the shooting ISO.
Actually, a Kodak app note I read suggested that White should be
considered to be 106% reflectance rather than just 100% (ISO is actually
based on 18% Gray).
So, I don't see why exposure is based on a separate system rather than
the histogram of the sensor's output -- this is an electronic system and
it should have AGC. As I suggested, you should be able to set the
aperture and the shutter and read the ISO that will be used or the
screen would turn Red if it would be too low. Or, you can have
automatic exposure that works from the video (preview) signal -- video
cameras don't have separate exposure sensors.
NOTE that you do need a sensor for automatic flash but that is really
just relocating the flash sensor from the flash unit to inside the
camera where it reads the reflection off of the sensor. You still have
to set a reasonable aperture manually.
Say you want a shot of small text and you want to make sure that
the text is readable. With only 720x480 or even 1920x1080 it
might not be. With 14 Mpixel that shouldn't be a problem. And I
kinda doubt that anyone makes a 14 Mpixel display.
The optical finder isn't going to do that either. You normally
have a higher resolution LCD on the back of the camera.
On mine the viewfinder and the larger display are both speced at a
whopping "113,000 (approx) pixels". That works out to only 291x388.
I suppose having them both be the same resolution makes the software
easier. I have yet to find a 720x480 panel. For 1920x1080 there is
a large laptop or 2 with a TN panel, otherwise it is 23" or larger.
A still camera is going to be a lot different than a video camera.
Large format backs have a Peltier cooler to cool the sensor
chip to reduce noise.
How do they prevent condensation?
That is a good question! This is limited to the moisture in the
air in the camera or between the protective glass and the sensor.
After it gets to 0 C, won't the condensation (now frozen) evaporate
(actually sublime)? IAC, if there is a protective glass over the
sensor, a desiccant will solve the problem.
According to the fine manual, mine will issue a condensation warning,
so it must have some sort of condensation sensor. As far as I know
it doesn't have a cooler. I assume they would brag about it if it
did.
You are still going to have issues at over 95% relative humidity.
With an OpenCamera and electronic sensor instead of film you
could program whatever type of metering you like.
Yes, a digital camera already has the ultimate auto exposure system
in it -- the image sensor. The issue is what to do if the entire
brightness range won't fit into the RAW format.
Are you saying that the sensor has a wider brightness range than the
RAW format? Sounds like the RAW format is defective. Obviously we
want to be able to store all the data the sensor can provide.
Actually not. If there were no noise, this would be infinite. But, we
have noise.
Ansel Adams must be rolling over in his grave.
Like film, an electronic camera can't always record the entire
brightness range of the subject. AFAIK, the RAW format stores all of
the sensor's useful brightness range based on a signal to noise ratio.
In theory, you could adjust the range (change the Gamma) that the RAW
file records. EXR/HDR would be a useful feature, or this is the
electronic equivalent of the Zone System.
--
JRT
_______________________________________________
Open-hardware mailing list
[email protected]
http://lists.duskglow.com/mailman/listinfo/open-hardware
