Add GEM_GRAY_EQUALIZE for low-contrast VIN images

dark_vin.png (faint green text on near-black) fails even with
GTM_INVERTED because the contrast is too low for text detection.
- Add GEM_GRAY_EQUALIZE as fallback enhancement in ip_recognize_text
  and tls_vin_text to boost contrast via histogram equalization
- Increase text detection sensitivity from 7 to 9

Author: Tom-Dynamsoft

lab/vin-scanner/template.json

@@ -261,13 +261,13 @@
       "Name": "ip_recognize_text",
       "BinarizationModes": [{ "BinarizationThreshold": -1, "BlockSizeX": 0, "BlockSizeY": 0, "EnableFillBinaryVacancy": 1, "GrayscaleEnhancementModesIndex": -1, "Mode": "BM_LOCAL_BLOCK", "MorphOperation": "Close", "MorphOperationKernelSizeX": 0, "MorphOperationKernelSizeY": 0, "MorphShape": "Rectangle", "ThresholdCompensation": 10 }],
       "ColourConversionModes": [{ "BlueChannelWeight": -1, "GreenChannelWeight": -1, "Mode": "CICM_GENERAL", "RedChannelWeight": -1, "ReferChannel": "H_CHANNEL" }],
-      "GrayscaleEnhancementModes": [{ "Mode": "GEM_GENERAL", "Sensitivity": -1, "SharpenBlockSizeX": -1, "SharpenBlockSizeY": -1, "SmoothBlockSizeX": -1, "SmoothBlockSizeY": -1 }],
+      "GrayscaleEnhancementModes": [{ "Mode": "GEM_GENERAL", "Sensitivity": -1, "SharpenBlockSizeX": -1, "SharpenBlockSizeY": -1, "SmoothBlockSizeX": -1, "SmoothBlockSizeY": -1 }, { "Mode": "GEM_GRAY_EQUALIZE", "Sensitivity": 9, "SharpenBlockSizeX": -1, "SharpenBlockSizeY": -1, "SmoothBlockSizeX": -1, "SmoothBlockSizeY": -1 }],
       "GrayscaleTransformationModes": [{ "Mode": "GTM_INVERTED" }, { "Mode": "GTM_ORIGINAL" }],
       "IfEraseTextZone": 0,
       "RegionPredetectionModes": [{ "AspectRatioRange": "[]", "FindAccurateBoundary": 0, "ForeAndBackgroundColours": "[]", "HeightRange": "[]", "ImageParameterName": "", "MeasuredByPercentage": 1, "MinImageDimension": 262144, "Mode": "RPM_GENERAL", "RelativeRegions": "[]", "Sensitivity": 1, "SpatialIndexBlockSize": 5, "WidthRange": "[]" }],
       "ScaleDownThreshold": 2300,
       "ScaleUpModes": [{ "AcuteAngleWithXThreshold": -1, "LetterHeightThreshold": 0, "Mode": "SUM_AUTO", "ModuleSizeThreshold": 0, "TargetLetterHeight": 0, "TargetModuleSize": 0 }],
-      "TextDetectionMode": { "CharHeightRange": [5, 1000, 1], "Direction": "HORIZONTAL", "MaxSpacingInALine": -1, "Mode": "TTDM_LINE", "Sensitivity": 7, "StringLengthRange": null },
+      "TextDetectionMode": { "CharHeightRange": [5, 1000, 1], "Direction": "HORIZONTAL", "MaxSpacingInALine": -1, "Mode": "TTDM_LINE", "Sensitivity": 9, "StringLengthRange": null },
       "TextureDetectionModes": [{ "Mode": "TDM_GENERAL_WIDTH_CONCENTRATION", "Sensitivity": 5 }]
     }
   ],
@@ -336,7 +336,7 @@
       "TextLinesCount": 1,
       "BinarizationModes": [{ "BinarizationThreshold": -1, "BlockSizeX": 11, "BlockSizeY": 11, "EnableFillBinaryVacancy": 1, "GrayscaleEnhancementModesIndex": -1, "Mode": "BM_LOCAL_BLOCK", "MorphOperation": "Erode", "MorphOperationKernelSizeX": 0, "MorphOperationKernelSizeY": 0, "MorphShape": "Rectangle", "ThresholdCompensation": 10 }],
       "CharacterNormalizationModes": [{ "Mode": "CNM_AUTO", "MorphArgument": "3", "MorphOperation": "Close" }],
-      "GrayscaleEnhancementModes": [{ "Mode": "GEM_GENERAL", "Sensitivity": 5, "SharpenBlockSizeX": 3, "SharpenBlockSizeY": 3, "SmoothBlockSizeX": 3, "SmoothBlockSizeY": 3 }],
+      "GrayscaleEnhancementModes": [{ "Mode": "GEM_GENERAL", "Sensitivity": 5, "SharpenBlockSizeX": 3, "SharpenBlockSizeY": 3, "SmoothBlockSizeX": 3, "SmoothBlockSizeY": 3 }, { "Mode": "GEM_GRAY_EQUALIZE", "Sensitivity": 9, "SharpenBlockSizeX": -1, "SharpenBlockSizeY": -1, "SmoothBlockSizeX": -1, "SmoothBlockSizeY": -1 }],
       "ConcatResults": 0,
       "ConcatSeparator": "\n",
       "ConcatStringLengthRange": [3, 200],