Facing problem in plotting histogram of DCT coefficient of an image

1. What are DCT coefficients in image?
2. Why Discrete Cosine Transform is appropriate for image compression?
3. Why was DCT chosen as transform domain for JPEG?

What are DCT coefficients in image?

DCT coefficient (0,0) is the DC coefficient, or average sample value. Since natural images tend to vary only slightly from sample to sample, low frequency coefficients are typically larger values and high frequency coefficients are typically smaller values. The 8×8 DCT is defined in Figure 5.21.

Why Discrete Cosine Transform is appropriate for image compression?

Discrete Cosine Transform is used in lossy image compression because it has very strong energy compaction, i.e., its large amount of information is stored in very low frequency component of a signal and rest other frequency having very small data which can be stored by using very less number of bits (usually, at most 2 ...

Why was DCT chosen as transform domain for JPEG?

DCT has cosine function which is easier to compute and the number of coefficients become less. Thus, DCT can result more accurate image reconstruction even if the JPEG is lossy transformation. There is one step called quantization where less important pixels are discarded according to the frequency distribution.