line art (#5052)

## Summary
- introduce a shared line art conversion interface and proprietary
ImageMagick-backed implementation
- have the compress controller optionally autowire the enterprise
service before running per-image line art processing
- remove ImageMagick command details from core by delegating conversions
through the proprietary service

## Testing
- not run (not requested)


------
[Codex
Task](https://chatgpt.com/codex/tasks/task_b_6928aecceaf083289a9269b1ca99307e)

---------

Co-authored-by: James Brunton <[email protected]>

app/common/src/main/java/stirling/software/SPDF/config/EndpointConfiguration.java

@@ -491,6 +491,9 @@ public class EndpointConfiguration {
         addEndpointToGroup("Ghostscript", "repair");
         addEndpointToGroup("Ghostscript", "compress-pdf");
 
+        /* ImageMagick */
+        addEndpointToGroup("ImageMagick", "compress-pdf");
+
         /* tesseract */
         addEndpointToGroup("tesseract", "ocr-pdf");
 
@@ -574,6 +577,7 @@ public class EndpointConfiguration {
                 || "Javascript".equals(group)
                 || "Weasyprint".equals(group)
                 || "Pdftohtml".equals(group)
+                || "ImageMagick".equals(group)
                 || "rar".equals(group);
     }
 

app/common/src/main/java/stirling/software/common/model/ApplicationProperties.java

@@ -653,6 +653,7 @@ public class ApplicationProperties {
             private int weasyPrintSessionLimit;
             private int installAppSessionLimit;
             private int calibreSessionLimit;
+            private int imageMagickSessionLimit;
             private int qpdfSessionLimit;
             private int tesseractSessionLimit;
             private int ghostscriptSessionLimit;
@@ -690,6 +691,10 @@ public class ApplicationProperties {
                 return calibreSessionLimit > 0 ? calibreSessionLimit : 1;
             }
 
+            public int getImageMagickSessionLimit() {
+                return imageMagickSessionLimit > 0 ? imageMagickSessionLimit : 4;
+            }
+
             public int getGhostscriptSessionLimit() {
                 return ghostscriptSessionLimit > 0 ? ghostscriptSessionLimit : 8;
             }
@@ -719,6 +724,8 @@ public class ApplicationProperties {
             @JsonProperty("calibretimeoutMinutes")
             private long calibreTimeoutMinutes;
 
+            private long imageMagickTimeoutMinutes;
+
             private long tesseractTimeoutMinutes;
             private long qpdfTimeoutMinutes;
             private long ghostscriptTimeoutMinutes;
@@ -756,6 +763,10 @@ public class ApplicationProperties {
                 return calibreTimeoutMinutes > 0 ? calibreTimeoutMinutes : 30;
             }
 
+            public long getImageMagickTimeoutMinutes() {
+                return imageMagickTimeoutMinutes > 0 ? imageMagickTimeoutMinutes : 30;
+            }
+
             public long getGhostscriptTimeoutMinutes() {
                 return ghostscriptTimeoutMinutes > 0 ? ghostscriptTimeoutMinutes : 30;
             }

app/common/src/main/java/stirling/software/common/service/LineArtConversionService.java

@@ -0,0 +1,12 @@
+package stirling.software.common.service;
+
+import java.io.IOException;
+
+import org.apache.pdfbox.pdmodel.PDDocument;
+import org.apache.pdfbox.pdmodel.graphics.image.PDImageXObject;
+
+public interface LineArtConversionService {
+    PDImageXObject convertImageToLineArt(
+            PDDocument doc, PDImageXObject originalImage, double threshold, int edgeLevel)
+            throws IOException;
+}

app/common/src/main/java/stirling/software/common/util/ProcessExecutor.java

@@ -86,6 +86,11 @@ public class ProcessExecutor {
                                                 .getProcessExecutor()
                                                 .getSessionLimit()
                                                 .getCalibreSessionLimit();
+                                case IMAGEMAGICK ->
+                                        applicationProperties
+                                                .getProcessExecutor()
+                                                .getSessionLimit()
+                                                .getImageMagickSessionLimit();
                                 case GHOSTSCRIPT ->
                                         applicationProperties
                                                 .getProcessExecutor()
@@ -141,6 +146,11 @@ public class ProcessExecutor {
                                                 .getProcessExecutor()
                                                 .getTimeoutMinutes()
                                                 .getCalibreTimeoutMinutes();
+                                case IMAGEMAGICK ->
+                                        applicationProperties
+                                                .getProcessExecutor()
+                                                .getTimeoutMinutes()
+                                                .getImageMagickTimeoutMinutes();
                                 case GHOSTSCRIPT ->
                                         applicationProperties
                                                 .getProcessExecutor()
@@ -301,6 +311,7 @@ public class ProcessExecutor {
         WEASYPRINT,
         INSTALL_APP,
         CALIBRE,
+        IMAGEMAGICK,
         TESSERACT,
         QPDF,
         GHOSTSCRIPT,

app/core/src/main/java/stirling/software/SPDF/config/ExternalAppDepConfig.java

@@ -46,6 +46,7 @@ public class ExternalAppDepConfig {
                         put("qpdf", List.of("qpdf"));
                         put("tesseract", List.of("tesseract"));
                         put("rar", List.of("rar")); // Required for real CBR output
+                        put("magick", List.of("ImageMagick"));
                     }
                 };
     }
@@ -128,6 +129,7 @@ public class ExternalAppDepConfig {
         checkDependencyAndDisableGroup("pdftohtml");
         checkDependencyAndDisableGroup(unoconvPath);
         checkDependencyAndDisableGroup("rar");
+        checkDependencyAndDisableGroup("magick");
         // Special handling for Python/OpenCV dependencies
         boolean pythonAvailable = isCommandAvailable("python3") || isCommandAvailable("python");
         if (!pythonAvailable) {

app/core/src/main/java/stirling/software/SPDF/controller/api/misc/CompressController.java

@@ -28,10 +28,13 @@ import org.apache.pdfbox.pdmodel.PDResources;
 import org.apache.pdfbox.pdmodel.graphics.PDXObject;
 import org.apache.pdfbox.pdmodel.graphics.form.PDFormXObject;
 import org.apache.pdfbox.pdmodel.graphics.image.PDImageXObject;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.ModelAttribute;
 import org.springframework.web.multipart.MultipartFile;
+import org.springframework.web.server.ResponseStatusException;
 
 import io.swagger.v3.oas.annotations.Operation;
 
@@ -44,6 +47,7 @@ import stirling.software.SPDF.model.api.misc.OptimizePdfRequest;
 import stirling.software.common.annotations.AutoJobPostMapping;
 import stirling.software.common.annotations.api.MiscApi;
 import stirling.software.common.service.CustomPDFDocumentFactory;
+import stirling.software.common.service.LineArtConversionService;
 import stirling.software.common.util.ExceptionUtils;
 import stirling.software.common.util.GeneralUtils;
 import stirling.software.common.util.ProcessExecutor;
@@ -58,6 +62,9 @@ public class CompressController {
     private final CustomPDFDocumentFactory pdfDocumentFactory;
     private final EndpointConfiguration endpointConfiguration;
 
+    @Autowired(required = false)
+    private LineArtConversionService lineArtConversionService;
+
     private boolean isQpdfEnabled() {
         return endpointConfiguration.isGroupEnabled("qpdf");
     }
@@ -66,6 +73,10 @@ public class CompressController {
         return endpointConfiguration.isGroupEnabled("Ghostscript");
     }
 
+    private boolean isImageMagickEnabled() {
+        return endpointConfiguration.isGroupEnabled("ImageMagick");
+    }
+
     @Data
     @AllArgsConstructor
     @NoArgsConstructor
@@ -660,6 +671,9 @@ public class CompressController {
         Integer optimizeLevel = request.getOptimizeLevel();
         String expectedOutputSizeString = request.getExpectedOutputSize();
         Boolean convertToGrayscale = request.getGrayscale();
+        Boolean convertToLineArt = request.getLineArt();
+        Double lineArtThreshold = request.getLineArtThreshold();
+        Integer lineArtEdgeLevel = request.getLineArtEdgeLevel();
         if (expectedOutputSizeString == null && optimizeLevel == null) {
             throw new Exception("Both expected output size and optimize level are not specified");
         }
@@ -689,6 +703,26 @@ public class CompressController {
                 optimizeLevel = determineOptimizeLevel(sizeReductionRatio);
             }
 
+            if (Boolean.TRUE.equals(convertToLineArt)) {
+                if (lineArtConversionService == null) {
+                    throw new ResponseStatusException(
+                            HttpStatus.FORBIDDEN,
+                            "Line art conversion is unavailable - ImageMagick service not found");
+                }
+                if (!isImageMagickEnabled()) {
+                    throw new IOException(
+                            "ImageMagick is not enabled but line art conversion was requested");
+                }
+                double thresholdValue =
+                        lineArtThreshold == null
+                                ? 55d
+                                : Math.min(100d, Math.max(0d, lineArtThreshold));
+                int edgeLevel =
+                        lineArtEdgeLevel == null ? 1 : Math.min(3, Math.max(1, lineArtEdgeLevel));
+                currentFile =
+                        applyLineArtConversion(currentFile, tempFiles, thresholdValue, edgeLevel);
+            }
+
             boolean sizeMet = false;
             boolean imageCompressionApplied = false;
             boolean externalCompressionApplied = false;
@@ -810,6 +844,75 @@ public class CompressController {
         }
     }
 
+    private Path applyLineArtConversion(
+            Path currentFile, List<Path> tempFiles, double threshold, int edgeLevel)
+            throws IOException {
+
+        Path lineArtFile = Files.createTempFile("lineart_output_", ".pdf");
+        tempFiles.add(lineArtFile);
+
+        try (PDDocument doc = pdfDocumentFactory.load(currentFile.toFile())) {
+            Map<String, List<ImageReference>> uniqueImages = findImages(doc);
+            CompressionStats stats = new CompressionStats();
+            stats.uniqueImagesCount = uniqueImages.size();
+            calculateImageStats(uniqueImages, stats);
+
+            Map<String, PDImageXObject> convertedImages =
+                    createLineArtImages(doc, uniqueImages, stats, threshold, edgeLevel);
+
+            replaceImages(doc, uniqueImages, convertedImages, stats);
+
+            log.info(
+                    "Applied line art conversion to {} unique images ({} total references)",
+                    stats.uniqueImagesCount,
+                    stats.totalImages);
+
+            doc.save(lineArtFile.toString());
+            return lineArtFile;
+        }
+    }
+
+    private Map<String, PDImageXObject> createLineArtImages(
+            PDDocument doc,
+            Map<String, List<ImageReference>> uniqueImages,
+            CompressionStats stats,
+            double threshold,
+            int edgeLevel)
+            throws IOException {
+
+        Map<String, PDImageXObject> convertedImages = new HashMap<>();
+
+        for (Entry<String, List<ImageReference>> entry : uniqueImages.entrySet()) {
+            String imageHash = entry.getKey();
+            List<ImageReference> references = entry.getValue();
+            if (references.isEmpty()) continue;
+
+            PDImageXObject originalImage = getOriginalImage(doc, references.get(0));
+
+            int originalSize = (int) originalImage.getCOSObject().getLength();
+            stats.totalOriginalBytes += originalSize;
+
+            PDImageXObject converted =
+                    lineArtConversionService.convertImageToLineArt(
+                            doc, originalImage, threshold, edgeLevel);
+            convertedImages.put(imageHash, converted);
+            stats.compressedImages++;
+
+            int convertedSize = (int) converted.getCOSObject().getLength();
+            stats.totalCompressedBytes += convertedSize * references.size();
+
+            double reductionPercentage = 100.0 - ((convertedSize * 100.0) / originalSize);
+            log.info(
+                    "Image hash {}: Line art conversion {} → {} (reduced by {}%)",
+                    imageHash,
+                    GeneralUtils.formatBytes(originalSize),
+                    GeneralUtils.formatBytes(convertedSize),
+                    String.format("%.1f", reductionPercentage));
+        }
+
+        return convertedImages;
+    }
+
     // Run Ghostscript compression
     private void applyGhostscriptCompression(
             OptimizePdfRequest request, int optimizeLevel, Path currentFile, List<Path> tempFiles)

app/core/src/main/java/stirling/software/SPDF/controller/api/misc/ConfigController.java

@@ -230,4 +230,10 @@ public class ConfigController {
         }
         return ResponseEntity.ok(result);
     }
+
+    @GetMapping("/group-enabled")
+    public ResponseEntity<Boolean> isGroupEnabled(@RequestParam(name = "group") String group) {
+        boolean enabled = endpointConfiguration.isGroupEnabled(group);
+        return ResponseEntity.ok(enabled);
+    }
 }

app/core/src/main/java/stirling/software/SPDF/controller/web/ReactRoutingController.java

@@ -74,13 +74,13 @@ public class ReactRoutingController {
     }
 
     @GetMapping(
-            "/{path:^(?!api|static|robots\\.txt|favicon\\.ico|manifest.*\\.json|pipeline|pdfjs|pdfjs-legacy|fonts|images|files|css|js|assets|locales|modern-logo|classic-logo|Login|og_images|samples)[^\\.]*$}")
+            "/{path:^(?!api|static|robots\\.txt|favicon\\.ico|manifest.*\\.json|pipeline|pdfjs|pdfjs-legacy|pdfium|fonts|images|files|css|js|assets|locales|modern-logo|classic-logo|Login|og_images|samples)[^\\.]*$}")
     public ResponseEntity<String> forwardRootPaths(HttpServletRequest request) throws IOException {
         return serveIndexHtml(request);
     }
 
     @GetMapping(
-            "/{path:^(?!api|static|pipeline|pdfjs|pdfjs-legacy|fonts|images|files|css|js|assets|locales|modern-logo|classic-logo|Login|og_images|samples)[^\\.]*}/{subpath:^(?!.*\\.).*$}")
+            "/{path:^(?!api|static|pipeline|pdfjs|pdfjs-legacy|pdfium|fonts|images|files|css|js|assets|locales|modern-logo|classic-logo|Login|og_images|samples)[^\\.]*}/{subpath:^(?!.*\\.).*$}")
     public ResponseEntity<String> forwardNestedPaths(HttpServletRequest request)
             throws IOException {
         return serveIndexHtml(request);

app/core/src/main/java/stirling/software/SPDF/model/api/misc/OptimizePdfRequest.java

@@ -45,4 +45,26 @@ public class OptimizePdfRequest extends PDFFile {
             requiredMode = Schema.RequiredMode.REQUIRED,
             defaultValue = "false")
     private Boolean grayscale = false;
+
+    @Schema(
+            description =
+                    "Whether to convert images to high-contrast line art using ImageMagick. Default is false.",
+            requiredMode = Schema.RequiredMode.NOT_REQUIRED,
+            defaultValue = "false")
+    private Boolean lineArt = false;
+
+    @Schema(
+            description = "Threshold to use for line art conversion (0-100).",
+            requiredMode = Schema.RequiredMode.NOT_REQUIRED,
+            defaultValue = "55")
+    private Double lineArtThreshold = 55d;
+
+    @Schema(
+            description =
+                    "Edge detection strength to use for line art conversion (1-3). This maps to"
+                            + " ImageMagick's -edge radius.",
+            requiredMode = Schema.RequiredMode.NOT_REQUIRED,
+            defaultValue = "1",
+            allowableValues = {"1", "2", "3"})
+    private Integer lineArtEdgeLevel = 1;
 }

app/core/src/main/resources/settings.yml.template

@@ -224,6 +224,7 @@ processExecutor:
     weasyPrintSessionLimit: 16
     installAppSessionLimit: 1
     calibreSessionLimit: 1
+    imageMagickSessionLimit: 4
     ghostscriptSessionLimit: 8
     ocrMyPdfSessionLimit: 2
   timeoutMinutes: # Process executor timeout in minutes
@@ -233,6 +234,7 @@ processExecutor:
     weasyPrinttimeoutMinutes: 30
     installApptimeoutMinutes: 60
     calibretimeoutMinutes: 30
+    imageMagickTimeoutMinutes: 30
     tesseractTimeoutMinutes: 30
     qpdfTimeoutMinutes: 30
     ghostscriptTimeoutMinutes: 30

app/proprietary/src/main/java/stirling/software/proprietary/service/ImageMagickLineArtConversionService.java

@@ -0,0 +1,81 @@
+package stirling.software.proprietary.service;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Locale;
+
+import javax.imageio.ImageIO;
+
+import org.apache.pdfbox.pdmodel.PDDocument;
+import org.apache.pdfbox.pdmodel.graphics.image.PDImageXObject;
+import org.springframework.stereotype.Service;
+
+import lombok.extern.slf4j.Slf4j;
+
+import stirling.software.common.service.LineArtConversionService;
+import stirling.software.common.util.ProcessExecutor;
+import stirling.software.common.util.ProcessExecutor.ProcessExecutorResult;
+
+@Slf4j
+@Service
+public class ImageMagickLineArtConversionService implements LineArtConversionService {
+
+    @Override
+    public PDImageXObject convertImageToLineArt(
+            PDDocument doc, PDImageXObject originalImage, double threshold, int edgeLevel)
+            throws IOException {
+
+        Path inputImage = Files.createTempFile("lineart_image_input_", ".png");
+        Path outputImage = Files.createTempFile("lineart_image_output_", ".tiff");
+
+        try {
+            ImageIO.write(originalImage.getImage(), "png", inputImage.toFile());
+
+            List<String> command = new ArrayList<>();
+            command.add("magick");
+            command.add(inputImage.toString());
+            command.add("-colorspace");
+            command.add("Gray");
+
+            // Edge-aware line art conversion using ImageMagick's built-in operators.
+            // -edge/-negate/-normalize are standard convert options (IM v6+/v7) that
+            // accentuate outlines before thresholding to a bilevel image.
+            command.add("-edge");
+            command.add(String.valueOf(edgeLevel));
+            command.add("-negate");
+            command.add("-normalize");
+
+            command.add("-type");
+            command.add("Bilevel");
+            command.add("-threshold");
+            command.add(String.format(Locale.ROOT, "%.1f%%", threshold));
+            command.add("-compress");
+            command.add("Group4");
+            command.add(outputImage.toString());
+
+            ProcessExecutorResult result =
+                    ProcessExecutor.getInstance(ProcessExecutor.Processes.IMAGEMAGICK)
+                            .runCommandWithOutputHandling(command);
+
+            if (result.getRc() != 0) {
+                log.warn(
+                        "ImageMagick line art conversion failed with return code: {}",
+                        result.getRc());
+                throw new IOException("ImageMagick line art conversion failed");
+            }
+
+            byte[] convertedBytes = Files.readAllBytes(outputImage);
+            return PDImageXObject.createFromByteArray(
+                    doc, convertedBytes, originalImage.getCOSObject().toString());
+        } catch (Exception e) {
+            log.warn("ImageMagick line art conversion failed", e);
+            throw new IOException("ImageMagick line art conversion failed", e);
+        } finally {
+            Files.deleteIfExists(inputImage);
+            Files.deleteIfExists(outputImage);
+        }
+    }
+}