Graphics Programs Reference
In-Depth Information
FIGURe 16.6
Previewing the Windows Bitmap file format in Save For Web
3.
Change the File Format drop-down to PNG-24 (24-bit or 8 bits
per channel). This format is non-lossy, meaning none of the visual
information is lost or compromised in the compression process. The
optimized preview looks identical to Figure 16.6. The file size of the
PNG-24 image is 1.205 MB, almost a 50 percent reduction compared
to the original.
pnG-24 images sup-
port varying degrees
of transparency.
4.
Change the File Format drop-down to PNG-8 (8 bits in one indexed
channel). The file size is down to 432.7 KB (19 percent of the origi-
nal). To achieve this reduction in file size, the number of colors was
reduced to 256 (8-bits). You can perceive a graininess that comes
from this color dithering. PNG-8 images are not good at representing
gradients because of the reduced number of colors. Open the Colors
drop-down and reduce the number to 64. The file size goes down to
301 KB but with unacceptable dithering (see Figure 16.7).
pnG-8 images are
often used for logos
on the Web. they
are best for repre-
senting contiguous
areas of solid color
with binary (on or
off) transparency.
5.
Change the File Format drop-down to JPEG. Select Very High from
the Compression Quality drop-down underneath the File Format
drop-down. The file size is 384 KB and the quality is excellent (see
Figure 16.8).
JpeG is a lossy
format; the level
of compression is
inversely related to
image quality.
