Feature/convert to grayscale (#3003)

# Description of Changes

Please provide a summary of the changes, including:

- What was changed
  -Grayscale Image Compression:
Modified the compressImagesInPDF method to optionally convert images to
grayscale during compression. This is
achieved by checking if the grayScale flag is true (or if the image is
already in grayscale) and then processing the image
   accordingly.

   UI Update:
Updated the compress-pdf.html file by adding a checkbox for grayscale
compression. Additionally, a new translation
key compress.grayscale.label with the text "Apply Grayscale for
Compression" has been added across all supported
   languages. 
- Why the change was made
  -Enhanced Compression Options:
This feature provides users with an option to compress images in PDFs
more effectively by reducing the color complexity, which can lead to
smaller file sizes.

Improved Flexibility:
It allows users to decide whether they want to maintain the original
color images or opt for a grayscale version.
- Any challenges encountered
- The translation for compress.grayscale.label was generated using an
automated translator, so it might not be completely accurate and could
require further review.

Closes #2603

---

## Checklist

### General

- [x] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [x] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md)
(if applicable)
- [x] I have performed a self-review of my own code
- [x] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [x] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md#6-testing)
for more details.

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

@@ -31,6 +31,7 @@ import io.swagger.v3.oas.annotations.Operation;
 import io.swagger.v3.oas.annotations.tags.Tag;
 
 import lombok.extern.slf4j.Slf4j;
+
 import stirling.software.SPDF.model.api.misc.OptimizePdfRequest;
 import stirling.software.SPDF.service.CustomPDDocumentFactory;
 import stirling.software.SPDF.utils.GeneralUtils;
@@ -51,7 +52,7 @@ public class CompressController {
         this.pdfDocumentFactory = pdfDocumentFactory;
     }
 
-    private void compressImagesInPDF(Path pdfFile, double initialScaleFactor) throws Exception {
+    private void compressImagesInPDF(Path pdfFile, double initialScaleFactor, boolean grayScale) throws Exception {
         byte[] fileBytes = Files.readAllBytes(pdfFile);
         try (PDDocument doc = Loader.loadPDF(fileBytes)) {
             double scaleFactor = initialScaleFactor;
@@ -76,11 +77,23 @@ public class CompressController {
                                     bufferedImage.getScaledInstance(
                                             newWidth, newHeight, Image.SCALE_SMOOTH);
 
-                            BufferedImage scaledBufferedImage =
+                            BufferedImage scaledBufferedImage;
-                                    new BufferedImage(
+                            if (grayScale
-                                            newWidth, newHeight, BufferedImage.TYPE_INT_RGB);
+                                    || bufferedImage.getType() == BufferedImage.TYPE_BYTE_GRAY) {
-                            scaledBufferedImage.getGraphics().drawImage(scaledImage, 0, 0, null);
+                                scaledBufferedImage =
-
+                                        new BufferedImage(
+                                                newWidth, newHeight, BufferedImage.TYPE_BYTE_GRAY);
+                                scaledBufferedImage
+                                        .getGraphics()
+                                        .drawImage(scaledImage, 0, 0, null);
+                            } else {
+                                scaledBufferedImage =
+                                        new BufferedImage(
+                                                newWidth, newHeight, BufferedImage.TYPE_INT_RGB);
+                                scaledBufferedImage
+                                        .getGraphics()
+                                        .drawImage(scaledImage, 0, 0, null);
+                            }
                             ByteArrayOutputStream compressedImageStream =
                                     new ByteArrayOutputStream();
                             ImageIO.write(scaledBufferedImage, "jpeg", compressedImageStream);
@@ -139,6 +152,7 @@ public class CompressController {
             }
 
             boolean sizeMet = false;
+            boolean grayscaleEnabled = Boolean.TRUE.equals(request.getGrayscale());
             while (!sizeMet && optimizeLevel <= 9) {
 
                 // Apply additional image compression for levels 6-9
@@ -152,7 +166,7 @@ public class CompressController {
                                 case 9 -> 0.5; // 60% of original size
                                 default -> 1.0;
                             };
-                    compressImagesInPDF(tempInputFile, scaleFactor);
+                    compressImagesInPDF(tempInputFile, scaleFactor, grayscaleEnabled);
                 }
 
                 // Run QPDF optimization
@@ -169,6 +183,7 @@ public class CompressController {
                 command.add("--compression-level=" + optimizeLevel);
                 command.add("--compress-streams=y");
                 command.add("--object-streams=generate");
+                command.add("--no-warn");
                 command.add(tempInputFile.toString());
                 command.add(tempOutputFile.toString());
 

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

@@ -29,4 +29,13 @@ public class OptimizePdfRequest extends PDFFile {
                     "Whether to normalize the PDF content for better compatibility. Default is false.",
             defaultValue = "false")
     private Boolean normalize = false;
+
+    @Schema(
+            description = "Whether to convert the PDF to grayscale. Default is false.",
+            defaultValue = "false")
+    private Boolean grayscale = false;
+
+    public Boolean getGrayscale() {
+        return grayscale;
+    }
 }

src/main/resources/messages_ar_AR.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=تطبيق التدرج الرمادي للضغط

src/main/resources/messages_az_AZ.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Sıxma üçün Boz Rəng Tətbiq Edin

src/main/resources/messages_bg_BG.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Версия
 validateSignature.cert.keyUsage=Предназначение на ключа за използване
 validateSignature.cert.selfSigned=Самостоятелно подписан
 validateSignature.cert.bits=битове
+compress.grayscale.label=Приложи сива скала за компресиране

src/main/resources/messages_ca_CA.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Aplicar escala de grisos per a la compressió

src/main/resources/messages_cs_CZ.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Verze
 validateSignature.cert.keyUsage=Použití klíče
 validateSignature.cert.selfSigned=Podepsaný sám sebou
 validateSignature.cert.bits=bitů
+compress.grayscale.label=Použít stupnici šedi pro kompresi

src/main/resources/messages_da_DK.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Anvend gråskala til komprimering

src/main/resources/messages_de_DE.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Schlüsselverwendung
 validateSignature.cert.selfSigned=Selbstsigniert
 validateSignature.cert.bits=bits
+compress.grayscale.label=Graustufen für Komprimierung anwenden

src/main/resources/messages_el_GR.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Έκδοση
 validateSignature.cert.keyUsage=Χρήση κλειδιού
 validateSignature.cert.selfSigned=Αυτο-υπογεγραμμένο
 validateSignature.cert.bits=bits
+compress.grayscale.label=Εφαρμογή κλίμακας του γκρι για συμπίεση

src/main/resources/messages_en_GB.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Apply Grayscale for Compression

src/main/resources/messages_en_US.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Apply Grayscale for Compression

src/main/resources/messages_es_ES.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Aplicar escala de grises para compresión

src/main/resources/messages_eu_ES.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Aplikatu grisezko eskala konpresiorako

src/main/resources/messages_fa_IR.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=نسخه
 validateSignature.cert.keyUsage=کاربرد کلید
 validateSignature.cert.selfSigned=با امضای خود
 validateSignature.cert.bits=بیت‌ها
+compress.grayscale.label=اعمال مقیاس خاکستری برای فشرده‌سازی

src/main/resources/messages_fr_FR.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Usage de la clé
 validateSignature.cert.selfSigned=Auto-signé
 validateSignature.cert.bits=bits
+compress.grayscale.label=Appliquer l'échelle de gris pour la compression

src/main/resources/messages_ga_IE.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Leagan
 validateSignature.cert.keyUsage=Úsáid Eochrach
 validateSignature.cert.selfSigned=Féin-Sínithe
 validateSignature.cert.bits=giotáin
+compress.grayscale.label=Cuir Scála Liath i bhFeidhm le Comhbhrú

src/main/resources/messages_hi_IN.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=संस्करण
 validateSignature.cert.keyUsage=कुंजी उपयोग
 validateSignature.cert.selfSigned=स्व-हस्ताक्षरित
 validateSignature.cert.bits=बिट्स
+compress.grayscale.label=संपीड़न के लिए ग्रेस्केल लागू करें

src/main/resources/messages_hr_HR.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Primijeni sivinu za kompresiju

src/main/resources/messages_hu_HU.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Verzió
 validateSignature.cert.keyUsage=Kulcshasználat
 validateSignature.cert.selfSigned=Önaláírt
 validateSignature.cert.bits=bit
+compress.grayscale.label=Szürkeárnyalatok alkalmazása tömörítéshez

src/main/resources/messages_id_ID.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Terapkan Skala Abu-Abu untuk Kompresi

src/main/resources/messages_it_IT.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Versione
 validateSignature.cert.keyUsage=Utilizzo della chiave
 validateSignature.cert.selfSigned=Autofirmato
 validateSignature.cert.bits=bit
+compress.grayscale.label=Applica scala di grigio per la compressione

src/main/resources/messages_ja_JP.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=バージョン
 validateSignature.cert.keyUsage=キーの使用法
 validateSignature.cert.selfSigned=自己署名
 validateSignature.cert.bits=ビット
+compress.grayscale.label=圧縮にグレースケールを適用する

src/main/resources/messages_ko_KR.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=버전
 validateSignature.cert.keyUsage=키 용도
 validateSignature.cert.selfSigned=자체 서명
 validateSignature.cert.bits=비트
+compress.grayscale.label=압축을 위해 그레이스케일 적용

src/main/resources/messages_nl_NL.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Grijsschaal toepassen voor compressie

src/main/resources/messages_no_NB.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Bruk gråskala for komprimering

src/main/resources/messages_pl_PL.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Zastosuj skalę szarości do kompresji

src/main/resources/messages_pt_BR.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Versão
 validateSignature.cert.keyUsage=Uso da chave
 validateSignature.cert.selfSigned=Autoassinados
 validateSignature.cert.bits=bits
+compress.grayscale.label=Aplicar escala de cinza para compressão

src/main/resources/messages_pt_PT.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Versão
 validateSignature.cert.keyUsage=Utilização da Chave
 validateSignature.cert.selfSigned=Auto-Assinado
 validateSignature.cert.bits=bits
+compress.grayscale.label=Aplicar escala de cinzentos para compressão

src/main/resources/messages_ro_RO.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Aplicare scală de gri pentru compresie

src/main/resources/messages_ru_RU.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Версия
 validateSignature.cert.keyUsage=Использование ключа
 validateSignature.cert.selfSigned=Самоподписанный
 validateSignature.cert.bits=бит
+compress.grayscale.label=Применить шкалу серого для сжатия

src/main/resources/messages_sk_SK.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Použiť odtiene šedej na kompresiu

src/main/resources/messages_sl_SI.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Različica
 validateSignature.cert.keyUsage=Uporaba ključa
 validateSignature.cert.selfSigned=Samopodpisano
 validateSignature.cert.bits=bits
+compress.grayscale.label=Uporabi sivinsko lestvico za stiskanje

src/main/resources/messages_sr_LATN_RS.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Primeni sivinu za kompresiju

src/main/resources/messages_sv_SE.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Tillämpa gråskala för komprimering

src/main/resources/messages_th_TH.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=ใช้ระดับสีเทาสำหรับการบีบอัด

src/main/resources/messages_tr_TR.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Sıkıştırma için Gri Ton Uygula

src/main/resources/messages_uk_UA.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Застосувати відтінки сірого для стиснення

src/main/resources/messages_vi_VN.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=Version
 validateSignature.cert.keyUsage=Key Usage
 validateSignature.cert.selfSigned=Self-Signed
 validateSignature.cert.bits=bits
+compress.grayscale.label=Áp dụng thang độ xám để nén

src/main/resources/messages_zh_BO.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=པར་གཞི།
 validateSignature.cert.keyUsage=ལྡེ་མིག་བེད་སྤྱོད།
 validateSignature.cert.selfSigned=རང་མིང་རྟགས།
 validateSignature.cert.bits=གནས།
+compress.grayscale.label=应用灰度进行压缩

src/main/resources/messages_zh_CN.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=版本
 validateSignature.cert.keyUsage=密钥用途
 validateSignature.cert.selfSigned=自签名
 validateSignature.cert.bits=比特
+compress.grayscale.label=应用灰度进行压缩

src/main/resources/messages_zh_TW.properties

@@ -1384,3 +1384,4 @@ validateSignature.cert.version=版本
 validateSignature.cert.keyUsage=金鑰用途
 validateSignature.cert.selfSigned=自我簽署
 validateSignature.cert.bits=位元
+compress.grayscale.label=應用灰階進行壓縮

src/main/resources/templates/misc/compress-pdf.html

@@ -39,6 +39,13 @@
                     <option value="8">8</option>
                     <option value="9">9</option>
                   </select>
+
+                  <div class="form-check mt-3">
+                    <input class="form-check-input" type="checkbox" name="grayscale" id="grayscaleCheck" value="true">
+                    <label class="form-check-label" for="grayscaleCheck" th:text="#{compress.grayscale.label}">
+                        Convert images to grayscale for better compression
+                    </label>
+                </div>
                 </div>
               </div>
               <div class="card mb-3">