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Merged
ModerRAS merged 1 commit into from
Jul 26, 2026
Merged

Test and harden long-image OCR slicing #369

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62 changes: 47 additions & 15 deletions TelegramSearchBot.Test/Service/AI/OCR/LongImageOcrSlicerTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -54,18 +54,39 @@ public void PlanSlices_WithoutBlankBand_UsesOverlapAndCoversImage() {
}

[Fact]
public void MergeResults_RemovesRepeatedBoundaryLines() {
public void PlanSlices_SingleBlankRowStillUsesOverlap() {
using var image = CreateDenseImage(800, 7000);
FillRows(image, LongImageOcrSlicer.TargetSliceHeight, LongImageOcrSlicer.TargetSliceHeight + 1, SKColors.White);

var slices = LongImageOcrSlicer.PlanSlices(image);

Assert.True(slices[1].HasOverlap);
AssertCompleteCoverage(slices, image.Height);
}

[Fact]
public void MergeResults_RemovesRepeatedBoundaryLinesFromOverlappingSlices() {
var result = LongImageOcrSlicer.MergeResults([
"第一段 重叠块一 重叠块二",
"重叠块一 重叠块二 第二段",
"第三段"
(new OcrImageSlice(0, 3072, false), "第一段 重叠块一 重叠块二"),
(new OcrImageSlice(2976, 3072, true), "重叠块一 重叠块二 第二段"),
(new OcrImageSlice(6048, 952, false), "第三段")
]);

Assert.Equal("第一段 重叠块一 重叠块二 第二段 第三段", result);
}

[Fact]
public async Task ExecuteAsync_LongImage_RunsSlicesInOrderAndMergesResults() {
public void MergeResults_PreservesRepeatedBoundaryTokensWithoutOverlap() {
var result = LongImageOcrSlicer.MergeResults([
(new OcrImageSlice(0, 3072, false), "第一段 2026"),
(new OcrImageSlice(3072, 3928, false), "2026 第二段")
]);

Assert.Equal("第一段 2026 2026 第二段", result);
}

[Fact]
public async Task ExecuteAsync_LongImage_PreservesRepeatedTokensAcrossSafeCut() {
var calls = new List<(int Width, int Height)>();
var responses = new Queue<string>(["第一段 重叠块", "重叠块 第二段"]);
var service = new PaddleOCRService(
Expand All @@ -82,6 +103,19 @@ public async Task ExecuteAsync_LongImage_RunsSlicesInOrderAndMergesResults() {
Assert.Equal(2, calls.Count);
Assert.All(calls, call => Assert.Equal(1000, call.Width));
Assert.All(calls, call => Assert.InRange(call.Height, 1, LongImageOcrSlicer.LongImageHeightThreshold));
Assert.Equal("第一段 重叠块 重叠块 第二段", result);
}

[Fact]
public async Task ExecuteAsync_OverlappingSlicesRemoveRepeatedBoundaryTokens() {
var responses = new Queue<string>(["第一段 重叠块", "重叠块 第二段"]);
var service = new PaddleOCRService(
Mock.Of<IConnectionMultiplexer>(),
payload => Task.FromResult(responses.Dequeue()));
using var stream = Encode(CreateDenseImage(1000, 5000));

var result = await service.ExecuteAsync(stream);

Assert.Equal("第一段 重叠块 第二段", result);
}

Expand Down Expand Up @@ -121,11 +155,11 @@ public async Task ExecuteAsync_WhenSliceFails_StopsProcessing() {
}

private static SKBitmap CreateDenseImage(int width, int height) {
var image = new SKBitmap(width, height);
for (var y = 0; y < height; y++) {
for (var x = 0; x < width; x++) {
image.SetPixel(x, y, x % 16 < 8 ? SKColors.Black : SKColors.White);
}
var image = CreateWhiteImage(width, height);
using var canvas = new SKCanvas(image);
using var paint = new SKPaint { Color = SKColors.Black };
for (var x = 0; x < width; x += 16) {
canvas.DrawRect(x, 0, 8, height, paint);
}
return image;
}
Expand All @@ -137,11 +171,9 @@ private static SKBitmap CreateWhiteImage(int width, int height) {
}

private static void FillRows(SKBitmap image, int start, int end, SKColor color) {
for (var y = start; y < end; y++) {
for (var x = 0; x < image.Width; x++) {
image.SetPixel(x, y, color);
}
}
using var canvas = new SKCanvas(image);
using var paint = new SKPaint { Color = color };
canvas.DrawRect(0, start, image.Width, end - start, paint);
}

private static MemoryStream Encode(SKBitmap image) {
Expand Down
22 changes: 16 additions & 6 deletions TelegramSearchBot/Service/AI/OCR/LongImageOcrSlicer.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@ internal static class LongImageOcrSlicer {
private const int AnalysisWidth = 256;
private const int MinimumSliceHeight = 1024;
private const int BrightnessDifferenceThreshold = 24;
private const int CutDensityRadius = 3;
private const double SafeRowDensityThreshold = 0.025;

internal static IReadOnlyList<OcrImageSlice> PlanSlices(SKBitmap image) {
Expand All @@ -33,7 +34,7 @@ internal static IReadOnlyList<OcrImageSlice> PlanSlices(SKBitmap image) {
var searchStart = Math.Max(top + MinimumSliceHeight, targetBottom - CutSearchRadius);
var searchEnd = Math.Min(image.Height - 1, targetBottom + CutSearchRadius);
var cut = FindBestCut(rowDensities, searchStart, searchEnd);
var safeCut = rowDensities[cut] <= SafeRowDensityThreshold;
var safeCut = AverageDensity(rowDensities, cut, CutDensityRadius) <= SafeRowDensityThreshold;
var hasOverlap = slices.Count > 0 && slices[^1].Top + slices[^1].Height > top;

slices.Add(new OcrImageSlice(top, cut - top, hasOverlap));
Expand All @@ -44,13 +45,22 @@ internal static IReadOnlyList<OcrImageSlice> PlanSlices(SKBitmap image) {
return slices;
}

internal static string MergeResults(IEnumerable<string> results) {
internal static string MergeResults(IEnumerable<(OcrImageSlice Slice, string Text)> results) {
var mergedTokens = new List<string>();
var previousSliceHadText = false;

foreach (var result in results.Where(result => !string.IsNullOrWhiteSpace(result))) {
var nextTokens = SplitTokens(result);
var duplicateTokenCount = FindDuplicateBoundary(mergedTokens, nextTokens);
foreach (var (slice, text) in results) {
if (string.IsNullOrWhiteSpace(text)) {
previousSliceHadText = false;
continue;
}

var nextTokens = SplitTokens(text);
var duplicateTokenCount = slice.HasOverlap && previousSliceHadText
? FindDuplicateBoundary(mergedTokens, nextTokens)
: 0;
mergedTokens.AddRange(nextTokens.Skip(duplicateTokenCount));
previousSliceHadText = true;
}

return string.Join(' ', mergedTokens);
Expand Down Expand Up @@ -97,7 +107,7 @@ private static int FindBestCut(double[] rowDensities, int searchStart, int searc
var bestScore = double.MaxValue;

for (var y = searchStart; y <= searchEnd; y++) {
var density = AverageDensity(rowDensities, y, 3);
var density = AverageDensity(rowDensities, y, CutDensityRadius);
var distancePenalty = Math.Abs(y - target) / ( double ) Math.Max(1, searchEnd - searchStart) * 0.01;
var score = density + distancePenalty;
if (score < bestScore) {
Expand Down
4 changes: 2 additions & 2 deletions TelegramSearchBot/Service/AI/OCR/PaddleOCRService.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -43,9 +43,9 @@ public async Task<string> ExecuteAsync(Stream file) {
return await ExecuteSliceAsync(image, slices[0]);
}

var results = new List<string>(slices.Count);
var results = new List<(OcrImageSlice Slice, string Text)>(slices.Count);
foreach (var slice in slices) {
results.Add(await ExecuteSliceAsync(image, slice));
results.Add((slice, await ExecuteSliceAsync(image, slice)));
}

return LongImageOcrSlicer.MergeResults(results);
Expand Down
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