Comparative study: enhancing legibility of ancient Indian script images from diverse stone background structures using 34 different pre-processing methods

Jayanthi, J.; Maheswari, P. Uma

doi:10.1186/s40494-024-01169-6

Heritage Science

Table 2 Comparative PSNR (Peak Signal-to-Noise Ratio) performance among various pre-processing methods

From: Comparative study: enhancing legibility of ancient Indian script images from diverse stone background structures using 34 different pre-processing methods

Methods	A	B	C	D	E	F	G	H	I	J	K	L	M
Brightness and contrast
Alpha, beta, gamma	28.66	28.95	28.7	28.1	29.23	28.67	28.05	27.82	28.41	28.38	28.33	29.12	28.18
Equalizer histogram	27.84	27.99	28.93	28.02	27.89	27.74	27.91	27.92	27.99	27.93	27.98	28.03	27.91
Equalizer histogram threshold	27.91	27.98	28.14	28.06	27.88	27.71	27.86	27.86	28.13	27.87	28	27.99	27.9
Smoothening image
Blur	28.04	27.79	27.81	27.88	28.14	27.65	27.83	27.97	27.79	27.97	27.89	28.05	28.05
Gaussian blur	28.02	27.8	27.82	27.81	28.08	27.66	27.81	27.85	27.79	27.89	27.87	28.03	27.93
Median blur	27.89	27.86	27.98	27.9	27.86	27.7	27.78	27.75	27.95	27.78	27.89	28.05	27.87
Smooth and remove noise
Bilateral filter	28.01	27.79	27.75	27.76	28.02	27.61	27.75	27.85	27.8	27.95	27.9	27.99	28.04
Structure elements morphological
Erosion	28.12	27.88	27.82	27.83	28.15	27.66	27.82	27.92	27.85	28.06	27.98	27.99	28.1
Dilation	28.01	27.79	27.75	27.76	28.02	27.61	27.75	27.85	27.8	27.95	27.9	27.99	28.04
MorpologyEx	28	27.88	27.75	27.81	28.07	27.59	27.78	27.89	27.8	27.96	27.88	27.96	28.08
Separation of dark and light region
Threshold	34.9	33.48	39.12	35.7	35.71	34.47	34.23	34.32	35.63	33.77	33.21	38.41	32.75
Adaptive threshold Gaussian	34.83	33.43	38.73	35.53	35.62	34.39	34.21	34.19	35.56	33.68	33.1	38.17	32.67
OSTU	34.5	33.39	38.41	35.21	35.23	34.42	34.08	33.91	35.34	33.46	32.99	38.37	52.52
Threshold triangle	34.89	33.48	39.1	35.13	35.31	34.33	34.21	34	35.65	33.34	33.07	36.95	32.45
Adaptive threshold mean	34.44	33.31	37.99	35.27	35.23	34.3	33.97	33.97	35.25	33.5	33	38.15	32.55
Adaptive threshold Gaussian	34.33	32.98	36.5	34.89	35.2	33.52	33.59	33.64	34.4	33.25	32.49	36.32	32.36
Adaptive threshold mean	34.36	32.96	36.85	35.05	35.1	33.47	33.69	33.63	35.25	33.33	32.48	36.15	32.36
Niblack	33.21	32.67	39.04	31.67	34.38	34.48	31.06	30.88	35.42	32.43	32.89	38.61	31.18
Savuola	28.66	28.95	28.7	28.1	29.23	28.67	28.05	27.82	28.41	28.38	28.33	29.12	28.18
Niblack dilation	34.83	33.43	38.73	35.53	35.63	34.39	34.21	34.19	35.56	33.68	33.1	38.17	32.67
Nilblack morphology	34.89	33.41	38.71	35.57	35.62	34.38	34.17	34.24	35.56	33.71	33.09	38.19	32.69
Nilblack erosion	34.77	33.43	38.49	35.39	35.58	34.38	34.12	34.19	35.56	33.63	33.1	38.14	32.67
Savoula dialtion	34.83	33.43	38.73	35.53	35.62	34.39	34.21	34.19	35.56	33.68	33.1	38.17	32.67
Savoula morphology	34.88	33.42	38.73	35.76	35.66	34.34	34.22	34.3	35.55	33.73	33.06	38.15	32.7
Savoula erosion	34.77	33.41	38.49	35.39	35.58	34.38	34.12	34.19	35.52	33.63	33.06	38.14	32.67
Nilblack k-means	34.83	33.43	38.54	35.52	35.62	34.39	34.21	34.19	35.55	33.69	33.1	38.16	32.66
Nilblack k-means noising	34.86	33.41	38.8	35.62	35.66	34.38	34.18	34.28	35.6	33.71	33.07	38.1	32.69
Nilblack k-means noising binarizations	34.41	33.05	36.59	34.96	35.26	33.57	33.64	33.74	34.51	33.31	32.56	36.25	32.36
Nilblack l-means noising binarization normalization	34.41	33.05	36.59	34.96	35.26	33.57	33.64	33.74	34.51	33.31	32.56	36.52	32.36
Edge detection
Sobelx	33.69	32.46	34.89	34.28	34.07	32.65	33.12	30.66	31.04	30.59	30.24	31.52	29.86
SobelY	33.75	32.63	35.31	34.21	34.13	32.83	33.07	34.32	33.69	32.61	31.82	33.92	31.92
Canny edge	34.3	33.04	36.63	34.98	34.94	33.53	33.65	34.19	33.64	32.63	31.81	34.24	31.92
Laplacian	30.99	30.42	31.38	31.39	31.54	30.39	30.73	33.91	34.45	33.29	32.55	36.33	32.31
Fast denosing	34	33	36	34	35.2	33.5	33.6	33.7	34.5	33.3	32.5	36.5	32.3

A dark-illegible, B flawless-bright-illegible, C flawless-bright-legible, D flawless-irregular-moderate, E highly impaired-irregular-illegible, F flawless-bright-legible, G flawless-bright-moderately legible, H flawless-dull—moderate, I highly impaired-dark-illegible, J impaired-dark-moderate, K very impaired-dusky dark-legible, L impaired-dull-moderately illegible, M impaired-dusky dark-moderate

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