CHAPTER 7 FILES AND FILE FORMATS 89- In each block, divides each of the 64 frequency
components by a separate quantization coeffi-
cient and rounds the results to integers. This
is when information is lost. The larger the
quantization coefficients, the more data is
discarded. Even the minimum possible
quantization coefficient, –1, loses some
information because the DCT function does
not normally output integers. The higher
frequencies in the block are quantized less
accurately (given larger coefficients) than
lower, because they are less visible to the
eye. The precious luminance data is
FIGURE 7.4
During JPEG
compression
chroma (color)
information is
sampled inter-
mittently.
Luminance
(brightness)
sampling occurs
at regular inter-
vals.
Downsampling is not
applicable to grayscale data.
As a result, color images are more
compressible than grayscale images.FIGURE 7.5
Blocks of pixels
8 ×8 are created
during JPEG
compression.