calibration

const (
	// MinQualityFactor is the minimum JPEG quality factor (standard range).
	MinQualityFactor = 1

	// MaxQualityFactor is the maximum JPEG quality factor (standard range).
	MaxQualityFactor = 100

	// DefaultCropPixels is the number of pixels to crop from each edge.
	DefaultCropPixels = 4

	// DefaultBlurEpsilon is the blur strength for the 3x3 low-pass filter.
	DefaultBlurEpsilon = 0.01

	// DoubleCompressionThreshold is the quality-factor gap (between the recovered
	// best primary quality and the stego quality) that flags double compression.
	// Lowered from 5 to 3 after a confirmed double-compressed F5 stego whose best
	// primary quality differed by 4 was missed; a saturated calibrated β is now
	// gated separately downstream so the lower threshold cannot cause a false
	// detection.
	DoubleCompressionThreshold = 3

	// CoeffRangeMin is the minimum DCT coefficient value analyzed in histograms.
	CoeffRangeMin = -5

	// CoeffRangeMax is the maximum DCT coefficient value analyzed in histograms.
	CoeffRangeMax = 5

	// NumLowFrequencyModes is the number of DCT frequency modes used in analysis.
	NumLowFrequencyModes = 3

	// FrequencyBandMode12 is the frequency band index for the Fridrich paper's
	// mode (1,2): first horizontal AC. Paper uses 1-indexed (k,l) where
	// (1,1)=DC, so 0-indexed array position is (0,1) and band = 0*8+1 = 1.
	FrequencyBandMode12 = 1

	// FrequencyBandMode21 is the frequency band index for the Fridrich paper's
	// mode (2,1): first vertical AC. 0-indexed (1,0); band = 1*8+0 = 8.
	FrequencyBandMode21 = 8

	// FrequencyBandMode22 is the frequency band index for the Fridrich paper's
	// mode (2,2): first diagonal AC. 0-indexed (1,1); band = 1*8+1 = 9.
	FrequencyBandMode22 = 9
)

const (
	// ErrCodeBetaOutOfRange is the error code returned when a beta value falls
	// outside the valid [0, 1] range during L2 distance calculation.
	ErrCodeBetaOutOfRange = "beta_out_of_range"

	// ErrCodeTestQualityRange is the error code returned when the test quality
	// factor is outside the valid [1, 100] range in the calibration pipeline.
	ErrCodeTestQualityRange = "test_quality_out_of_range"

	// ErrCodeFinalQualityRange is the error code returned when the final
	// quality factor is outside the valid [1, 100] range in the calibration
	// pipeline.
	ErrCodeFinalQualityRange = "final_quality_out_of_range"

	// ErrCodeStegoQualityRange is the error code returned when the stego
	// quality factor is outside the valid [1, 100] range in multi-QF
	// calibration.
	ErrCodeStegoQualityRange = "stego_quality_out_of_range"

	// ErrCodeNoQualityFactors is the error code returned when no quality
	// factors are provided for multi-QF calibration.
	ErrCodeNoQualityFactors = "no_quality_factors"

	// ErrCodeEmptyHistograms is the error code returned when histogram input
	// contains no data for calibration.
	ErrCodeEmptyHistograms = "empty_histograms"

	// ErrCodeDecodeStegoImage is the error code returned when the stego image
	// cannot be decoded during the calibration pipeline.
	ErrCodeDecodeStegoImage = "decode_stego_image"

	// ErrCodeConvertToYCbCr is the error code returned when RGB to YCbCr
	// color space conversion fails during the calibration pipeline.
	ErrCodeConvertToYCbCr = "convert_to_ycbcr"

	// ErrCodeCropImage is the error code returned when image cropping fails
	// during the calibration pipeline.
	ErrCodeCropImage = "crop_image"

	// ErrCodeApplyBlur is the error code returned when blur application fails
	// during the calibration pipeline.
	ErrCodeApplyBlur = "apply_blur"

	// ErrCodeConvertToRGB is the error code returned when YCbCr to RGB
	// color space conversion fails during the calibration pipeline.
	ErrCodeConvertToRGB = "convert_to_rgb"

	// ErrCodeIntermediateCompress is the error code returned when intermediate
	// JPEG compression fails during the double compression calibration step.
	ErrCodeIntermediateCompress = "intermediate_compress"

	// ErrCodeIntermediateDecode is the error code returned when decoding the
	// intermediate JPEG fails during the double compression calibration step.
	ErrCodeIntermediateDecode = "intermediate_decode"

	// ErrCodeRecompress is the error code returned when final JPEG
	// recompression fails during the calibration pipeline.
	ErrCodeRecompress = "recompress"

	// ErrCodeExtractCoverCoeffs is the error code returned when DCT
	// coefficient extraction from the recompressed image fails during the
	// calibration pipeline.
	ErrCodeExtractCoverCoeffs = "extract_cover_coefficients"
)