Sony DVBK-2000 - Manual (Page 37)

Technical information (continued)
About aspect ratio conversion
A DV formatted image file composes of 720 x 480
pixels (DVBK-2000) or 720 x 576 pixels (DVBK-2000E)
and each pixel is rectangular; taller than it is wide
(NTSC) or wider than it is tall (PAL).
However, since pixels on the PC are square, the image
overflows (NTSC) or is insufficient in number (PAL)
in the horizontal direction when displayed. To prevent
this, DV software converts the number of pixels in the
horizontal direction from 720 to 640 (DVBK-2000) or
720 to 768 (DVBK-2000E) before the image is
displayed.
And also, before image files (640 x 480 pixels for
DVBK-2000, 768 x 576 pixels for DVBK-2000E) created
by PC and saved in BMP/PICT or JPEG format are
encoded to the DV format, the number of pixels in the
horizontal direction is converted from 640 to 720
(DVBK-2000) or from 768 to 720 (DVBK-2000E).
This correction is called "Aspect Ratio Conversion".
The aspect ratio conversion during decode decreases
the data size because it decreases/increases the
number of the pixels.
Therefore, the image quality may be degraded when a
DV formatted image file is saved in BMP/PICT or
JPEG format after the aspect converted and it is
converted back to a DV formatted image file.
To prevent this, decode or encode an image file
without the aspect conversion.
For example, consider a case that an image is captured
from a DV equipment to your PC and record it as a
still image using a DV equipment after title is added.
1
Choose "Preferences" from the "File" menu, and
select "Decode".
2
Set "Aspect Ratio Conversion" to "Off" and
decode an image file without any correction.
3
Choose "Save as" from the "FUe" menu in Viewer
window and save the decoded image in BMP/
PICT or JPEG format.
4
Import the save image using the supplied Adobe
PhotoDduxe or the like and add an title.
Notice that when the image is encoded to the DV
format again, the added title is reduced in the
horizontal direction by 8/9 (DVBK-2000 NTSC)
o
expanded by 16 /15 (DVBK-2000E PAL).
Therefore, it is recommended that in advance a
title is expanded in the horizontal direction by 9 /
(DVBK-2000 NTSC) or reduced by 15/16 (DVBK-
2000E PAL).
Select "File" from the Album window and
"Import" from "File" to import the image to whic
the title is added.
The image file of 720 x 480 pixels (NTSC) or 720 x
576 pixels (PAL) is converted to a DV format file,
not Aspect-converted.
Thus you can add a title to an image without
degrading the quality. Try this method when you
want to surpress the degration too the minimum.
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