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Indlæg
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Mogens.Bildsøe- Nova
Jeg har kig på Qcam 6 pro. Kameraet bruger interlaced scan ved udlæsning (i modsætning til progressive scan), og sætter således en frame sammen af 2 separat udlæste fields. Hvad er fordele/ulemper ved de to metoder? Og, kan interlaced scan ha’ betydning, hvis man skal forsøge sig med fotometri? Der kan vel sagtens opstå forskelle mellem de 2 fields, når de udlæses hver for sig?
Mogens B
Hilsen Mogens B.
mstauning- Black Hole
Vender lige tilbage med nogle test skud der måske kan vise dig det, men det betyder intet for exponeringer der ikke er korte. For fotometri betyder det slet intet.
chrjensen- Super Giant
Mener du ikke at CCD’en er interlined?
Det betyder hvis jeg husker rigtigt , at udlæsning af CCD’en sker via nogle “kanaler” der løber vertikelt mellem de enkelte søjler af pixels. I en progressiv chip sker udlæsningen ved at ladningen overføres fra en celle til den næste. Interlined chips er derfor hurtigere at læse, mens prograssive chips har en højere følsomhed (ingen “kanaler” = større lysfølsomt område = større følsomhed).Mener at have læst at interlined chips kan give problemer ved fotometri hvis “peak’en” for en stjerne falder enten på en “kanal” eller på en lysfølsom pixel. Dette burde dog kunne undgås ved at vælge en teleskop/CCD kombination hvor aries disk’en fylder mindst 4 pixels (2×2).Er der nogle andre der kan bekrafte denne forklaring? Min hukomelse på området er lidt rusten.chrjensen 2009-01-13 17:41:09
thor- Moon
Hej,
Jeg læste en testrapport af ccd videokameraer i Sterne und Weltraum, se:
http://www.astronomycamerasblog.com/2008/05/22/test-report-in-german-magazine-sterne-und-weltraum/Her er det beskrevet at planetoptagelser med Watec 120 (som er et interlaced videokamera) giver en “bjælkeeffekt” (Balkeneffekt), dvs. en uønsket artefakt.
Grunden er, at atmosfæreuro udtværer billedet i tidsrummet mellem tegning af billedet på skærmen, og det sker først for hver anden linie med interlaced teknik; i tiden der går inden det næste sæt (de interlacede) linier bliver tegnet ændrer atmosfæreuroen. Resultatet er en bjælkeeffekt i det samlede billede af planeten.
Det har kun synlig effekt ved foto, ikke ved alm. obs. af tv-skærmen.håber det kan bruges til noget!
mvh
thor- Moon
hej igen,
mit indlæg er måske ikke relevant; indlægger er dog relevant for analog video, men det ved jeg ikke om dit kamera er, beklager forvirringen.
mvh
Mogens.Bildsøe- Nova
Hej og tak for svar. Thor, ingen grund til forvirring- er også aktuelt ved CCD foto.
Har læst lidt på google og fundet mange hits- her et, som forklarer forståeligt for alm. dødelige:Interline refererer til måden, hvorpå pixelværdier gemmes under udlæsning, mens interlaced/progressiv refererer til måden hvorpå udlæsningen foregår: 2 x field (interlaced: ulige rækker efterfulgt af ulige række, som derefter sammensættes til een frame) eller progressiv (alle pixels i rækkefølge)Det efgørende ved interlaced scan er derfor, om chippen lukkes elektronisk, så der ikke foregår eksponering under udlæsning, eller om der eksponeres under udæsning (hvorved field 2 jo eksponeres mens field 1 udlæses). Eksponerer f.eks. qcam 6 pro (som udlæser med interlaced scan) under udlæsning????Interlaced har, som Michael skriver, ingen betydning for længere eksponeringer (over ca. 15 s iflg. Henrik qcam).
Hilsen Mogens B.
mstauning- Black Hole
Som Thor skriver kommer der bjælker, men det kræver meget korte expo tider. Ved længere tider forsvinder det helt.
Jeg vil give Henrik ret i at man skal derop omkring, ved fokus tider (0,1 – 10 sek) ser jeg dem. Når jeg så lige laver en goto og tager en expo for at få center helt i øjet, gør jeg det med 30sek og der er ikke noget at se. Skal lige finde den PC jeg optog med Qcam sidst da den har filer liggende fra et par sekunder til 10min.
thor- Moon
Hej,
Jeg læste en testrapport af ccd videokameraer i Sterne und Weltraum, se:
http://www.astronomycamerasblog.com/2008/05/22/test-report-in-german-magazine-sterne-und-weltraum/Her er det beskrevet at planetoptagelser med Watec 120 (som er et interlaced videokamera) giver en “bjælkeeffekt” (Balkeneffekt), dvs. en uønsket artefakt.
Grunden er, at atmosfæreuro udtværer billedet i tidsrummet mellem tegning af billedet på skærmen, og det sker først for hver anden linie med interlaced teknik; i tiden der går inden det næste sæt (de interlacede) linier bliver tegnet ændrer atmosfæreuroen. Resultatet er en bjælkeeffekt i det samlede billede af planeten.
Det har kun synlig effekt ved foto, ikke ved alm. obs. af tv-skærmen.håber det kan bruges til noget!
mvh
motomandk- Main Sequence
Her er hele forklaringen:
Types of CCDs
The four
basic types of CCDs are Linear, Interline, Full-Frame, and
Frame-Transfer. A Linear CCD consists of a single row of pixels–all in
one line. To define an image, a Linear CCD must be scanned across the
plane of the image, building the picture row by row. It is, obviously,
a much slower process than using a sensor that captures the entire
image simultaneously. And, it requires the use of stepper motors, which
increases the complexity of the system, the potential for mechanical
misalignment and breakdown, and greater noise. Linear CCDs were more
common in the past than they are now, but they are still used in most
flatbed scanners and in digital camera scanner backs.Interline, Full-Frame, and Frame-Transfer designs are considered Area
Array CCDs, because they are composed of multiple rows and columns
forming a rectangular or square area.Interline
In an Interline CCD, each pixel has both a photodetector and a charge
storage area. The storage area is formed by shielding or masking part
of the pixel from light and using it only for the charge transfer
process. The masked areas for each pixel form a vertical charge
transfer channel that runs from the top of the array to the horizontal
shift register. Purists will tell you that this vertical masked region
used for charge transfer is the CCD portion of the image sensor,
because that’s where the charge-coupling occurs. To distinguish the
area from the entire chip (the CCD sensor), they sometimes call it the
VCCD, for Vertical CCD (or sloppily, just the CCD). The horizontal
shift register may also be called the HCCD. However, to avoid
confusion, we will not use VCCD or HCCD nomenclature. The area that
remains exposed to light is more sensibly called the aperture.The interline design allows the pixel’s electric charge to quickly be
shifted to an adjacent masked storage area where the charge can be
shifted down row by row to the horizontal shift register. The fast
transfer to the storage area frees up the pixel well to accept the next
batch of photons. In digital cameras, this quick availability of the
pixel aperture to accept the next frame of image data is what enables
the capture of video. The downside of the interline design is that a
significant portion of the sensor is no longer photosensitive, thereby
limiting the potential pixel density (“resolution”). To counter this,
interline CCDs require micro lenses to better direct the photons into
the photosensitive area of the pixel. Also, their design is more
complex to manufacture. Interline CCDs tend to be used primarily in
consumer digital cameras.Full-Frame CCDs
Full-Frame CCDs devote the entire pixel to image capture. Therefore,
when the charge transfer occurs, the pixel is busy and cannot continue
to capture photons. To keep the pixels from continuing to read
additional light when they are involved in charge transfer (which can
lead to light smear on the image), digital camera designers usually put
a mechanical shutter between or behind the camera lens. The only time a
mechanical shutter is not necessary on a digital camera with a
full-frame CCD is in shooting situations in which the duration and
amount of light is controlled externally, such as with studio strobe
lights. Full-frame CCDs are used in higher-end digital cameras, for
greater capture density.Frame-Transfer CCDs
Frame-Transfer CCDs are similar to Full-Frame, but they mask out half
of the array to provide temporary storage for the electric charges,
aptly called the “storage array”. Once an integration period ends and
the photosensitive pixels have acquired their charges, they are quickly
transferred to the storage array, and can operate without shutter
delay. This makes them very fast capture devices. But the subsequent
integration period overlaps the transfer time to the storage array
which causes image smear. Another downside is the larger size (and thus
higher cost) of Frame-Transfer CCDs to accommodate both the
photosensitive array and the storage array. Interline CCDs are an
improvement on this design and permit integration and transfer
simultaneously, causing only minimal image smear.Even though there are only a handful of CCD manufacturers, competition
is fierce among them. Differentiation among their sensors is a key
issue in attracting volume buyers. So, it should come as no surprise
that each manufacturer is working on varying and improving CCD
architecture. Here are just a few examples (We’ll cover additional
designs in future articles):Fuji’s Super CCD uses a unique honeycomb architecture of octagonal
pixels that makes maximum use of silicon real estate in the sensor.
Therefore, greater densities of pixels can be fit onto the CCD. The
shape of the pixel also allows for a larger area to be photosensitive.
Fuji claims better signal to noise ratio and better dynamic range with
this architecture. However, when we tested the first generation
consumer Super CCD in the Fujifilm 4700
digital camera last year, we were very disappointed in the quality of
the images produced. But the latest generation Fuji digital cameras
have been better optimized for the Super CCD technology. Our tests have
shown the pictures to be sharper than those taken with comparable
competitor cameras, and the overall image quality to be quite good.(See
our in-depth review of the Fujifilm FinePix S1 Pro.)Progressive vs Interlaced CCDs
Data is read out from a sensor using one of two methods–progressive or
interlaced. Similar to scan modes used in video, these methods relate
to the order in which the CCD columns of data are fed to the horizontal
transfer register and off the sensor.Progressive CCDs will read each line in the order in which they
appear in the image. Interlace CCDs will read first the even lines,
then the odd lines, and reintegrate them later through image processing.Interline CCDs over 1MP (which are the typical sensors used in consumer
digital camera sensors) tend to be interlaced devices, in which one row
of electrodes controls the vertical transfer of the charges from two
rows of pixels.In an ideal world, we would have sensors with CCD image quality and
CMOS intelligence. That is not currently possible. However, Kodak has
created an interline CCD–the KAI 2020 chip–which does some image
processing on the chip by adding clock drivers for double correlated
sampling. While Kodak will not call it an intelligent CCD (that’s the
domain of CMOS sensors that can do the analog-to-digital conversion, as
well as other image processing on chip), it calculates the dark current
(the baseline noise image that exists even when no light is present) of
the pixels and subtracts it from the illuminated image. This is a
popular method used in CMOS image sensors to neutralize noise and
artifacts. At present, the KAI 2020 is only an industrial sensor; it is
not used for digital cameras but is found in such applications as
automated inspections or traffic control.Philips’ Frame-Transfer CCD is a technology called True Frame sensor
architecture (which was developed by Philips, but also used by Sanyo).
The storage area in this sensor is shielded from light by a metal layer
and can hold only about one-fifth of the full charge capacity of the
pixel. It is used only for feeding the scene to preview on the LCD
viewfinder and for extracting information about the scene so that
exposure and other settings may be determined. If the camera is in
monitor or preview mode, the electrons are quickly sent into storage,
with four fifths of them dumped (and lost) into the silicon substrate.
But if it is in picture mode, all the electrons are quickly read out
with none sent to the storage area. The method of readout is
progressive, rather than interlaced, and speed is the primary advantage
of this arrangement. While a typical interline CCD has a frame rate of
about 5-10 frames per second (fps), Philips claims that their Frame
Transfer CCD has a frame rate of 30-60 fps. That’s true video speed.
We’d expect there to be problems with smear if no shutter exists,
however, because integration time would overlap readout time.En kommentar fra min side er, at ovenstående ikke omtaler ‘micro-lensing’ som er små linser der er ovenpå ‘fotobrønden og dækker hele brøndens area – dvs. at alle photoner der ‘lander’ på arealet vil blive ledt ned i brønden. Derved undgås den reduktion i følsomheden som ekstra elektronik til anti-blooming og interline eller påfører chippen.
/Henrik (H)
motomandk- Main Sequence
OBS!! ovenstående tyvstjålet fra ExtremeTech:
http://www.extremetech.com/article2/0,2845,1157575,00.asp/Henrik (H)
motomanDK 2009-01-13 21:00:06
norup- Super Giant
Kom i tanke om denne tråd da jeg i dag fangede en fugl med et interlaced kamera. Det demonstrerer, hvorfor det ikke egner sig til korte eksponeringer af noget, der ændrer sig hurtigt. Der optages 25 billeder/sek, men hvert billede består af to interlaced eksponeringer.
- Emnet 'Interlaced vs. progressive' er lukket for nye svar.