Enhancement of Color Images by Enhancement of Color Images by Scaling the DCT CoefficientsScaling the DCT Coefficients

INTRODUCTION

A majority of techniques advanced so far have focused on the enhancement of gray-level images in the spatial domain.

Different algorithms have been advanced for both color and grey level images in the block DCT domain, such as alpha rooting, multicontrast enhancement.

INTRODUCTION

The display of a color image depends upon three fundamental factors, namely

i) brightness, ii) contrast, iii) colors.

This paper presents a new technique for color enhancement in the compressed domain.

INTRODUCTION

None of these algorithms have considered the preservation of colors in the enhanced image.

In this work we have considered all three attributes while designing a simple computationally efficient algorithm.

ALGORITHM

Adjustment of Local Background Illumination

Preservation of Local Contrast

Preservation of Colors

Suppressing Blocking Artifacts

ALGORITHMInput: Y,U,V: DCTs of three components of a block.

Input Parameters: f(x) (the mapping function), Imax, Bmax, κ, σthresh, N (Block size)

Output:

1. Compute μ and σ.

2. If ( σ > σthresh),

2a. Decompose into (N/2) ×(N/2) DCT sub-blocks,

2b. For each block apply similar computations as described in Steps 3 through 5, and

2c. Combine 4 of these (N/2) ×(N/2) blocks into a single N×N DCT block and return.

ALGORITHM3. Compute the enhancement factor (κ) as follows:3a. κ= (f(Y(0,0)/N． Imax))/(Y(0,0)/N． Imax),3b. κ= min ( κ, (Bmax /μ+ κσ) ), and3c. κ= max(κ,1),4. Scale the coefficients:4a. = κY, and

4b. Apply on U and V for preserving colors.

End Color Enhancement by Scaling (CES)

RESULT

Enhancement of image18

RESULT

Enhancement of image22

RESULT

Enhancement of image24.

RESULT

報告完畢 !!謝謝各位 !!