New feature: ability to force color mode for a page

app/src/main/java/org/fairscan/app/MainActivity.kt

@@ -124,8 +124,7 @@ class MainActivity : ComponentActivity() {
             val currentScreen by viewModel.currentScreen.collectAsStateWithLifecycle()
             val liveAnalysisState by cameraViewModel.liveAnalysisState.collectAsStateWithLifecycle()
             val document by viewModel.documentUiModel.collectAsStateWithLifecycle()
-            val currentPageIndex by viewModel.currentPageIndex.collectAsStateWithLifecycle()
+            val documentUiState by viewModel.documentUiState.collectAsStateWithLifecycle()
-            val currentPageBitmap by viewModel.currentPageBitmap.collectAsStateWithLifecycle()
             val exportUiState by exportViewModel.uiState.collectAsStateWithLifecycle()
             val cameraPermission = rememberCameraPermissionState()
             CollectCameraEvents(cameraViewModel, viewModel)
@@ -180,11 +179,12 @@ class MainActivity : ComponentActivity() {
                     }
                     is Screen.Main.Document -> {
                         DocumentScreen (
-                            uiState = DocumentUiState(currentPageIndex, currentPageBitmap, document),
+                            uiState = documentUiState,
                             navigation = navigation,
                             onExportClick = onExportClick,
                             onDeleteImage =  { id -> viewModel.deletePage(id) },
                             onRotateImage = { id, clockwise -> viewModel.rotateImage(id, clockwise) },
+                            onToggleColorMode = { id -> viewModel.togglePageColorMode(id) },
                             onPageReorder = { id, newIndex -> viewModel.movePage(id, newIndex) },
                             onPageSelected = viewModel::onPageSelected
                         )

app/src/main/java/org/fairscan/app/MainViewModel.kt

@@ -15,13 +15,13 @@
 package org.fairscan.app
 
 import android.graphics.Bitmap
-import android.graphics.BitmapFactory
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import kotlinx.collections.immutable.persistentListOf
 import kotlinx.collections.immutable.toImmutableList
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
@@ -38,10 +38,14 @@ import org.fairscan.app.domain.CapturedPage
 import org.fairscan.app.domain.ScanPage
 import org.fairscan.app.ui.NavigationState
 import org.fairscan.app.ui.Screen
+import org.fairscan.app.ui.screens.document.CurrentPageUiState
+import org.fairscan.app.ui.screens.document.DocumentUiState
 import org.fairscan.app.ui.state.DocumentUiModel
 import org.fairscan.app.ui.state.PageThumbnail
+import org.fairscan.imageprocessing.ColorMode
 import kotlin.math.min
 
+@OptIn(ExperimentalCoroutinesApi::class)
 class MainViewModel(val imageRepository: ImageRepository, launchMode: LaunchMode): ViewModel() {
 
     private val _navigationState = MutableStateFlow(NavigationState.initial(launchMode))
@@ -68,21 +72,31 @@ class MainViewModel(val imageRepository: ImageRepository, launchMode: LaunchMode
         .stateIn(
             scope = viewModelScope,
             started = SharingStarted.Eagerly,
-            initialValue = DocumentUiModel(persistentListOf())
+            initialValue = DocumentUiModel()
         )
 
     private val _currentPageIndex = MutableStateFlow(0)
-    val currentPageIndex: StateFlow<Int> =
+
-        _currentPageIndex.stateIn(viewModelScope, SharingStarted.Eagerly, 0)
+    val currentPageUiState: Flow<CurrentPageUiState> =
-    @OptIn(ExperimentalCoroutinesApi::class)
+        combine(_currentPageIndex, _pages) { index, pages -> pages.getOrNull(index) }
-    val currentPageBitmap: StateFlow<Bitmap?> =
-        _currentPageIndex
-            .combine(_pages) { index, pages -> pages.getOrNull(index) }
             .mapLatest { page ->
-                page?.let { imageRepository.jpegBytes(it.key())?.toBitmap() }
+                page?.let {
+                    CurrentPageUiState(
+                        imageRepository.jpegBytes(it.key())?.toBitmap(),
+                        page.colorMode
+                    )
+                } ?: CurrentPageUiState()
             }
             .flowOn(Dispatchers.IO)
-            .stateIn(viewModelScope, SharingStarted.Eagerly, null)
+
+    val documentUiState: StateFlow<DocumentUiState> =
+        combine(_currentPageIndex, currentPageUiState, documentUiModel) { index, page, document ->
+            DocumentUiState(index, page, document)
+        }
+            .stateIn(
+                viewModelScope, SharingStarted.Eagerly,
+                DocumentUiState(0, CurrentPageUiState(), DocumentUiModel())
+            )
 
     fun onPageSelected(index: Int) {
         _currentPageIndex.value = index
@@ -90,6 +104,9 @@ class MainViewModel(val imageRepository: ImageRepository, launchMode: LaunchMode
 
     fun navigateTo(destination: Screen) {
         if (destination is Screen.Main.Document) {
+            require(_pages.value.isNotEmpty()) {
+                "Cannot navigate to DocumentScreen with zero pages"
+            }
             _currentPageIndex.value = min(_pages.value.size - 1, destination.initialPage)
         }
         _navigationState.update { it.navigateTo(destination) }
@@ -125,7 +142,6 @@ class MainViewModel(val imageRepository: ImageRepository, launchMode: LaunchMode
                 imageRepository.delete(id)
                 imageRepository.pages()
             }
-            _pages.value = pages
 
             if (pages.isEmpty()) {
                 navigateTo(Screen.Main.Camera)
@@ -133,6 +149,22 @@ class MainViewModel(val imageRepository: ImageRepository, launchMode: LaunchMode
             } else if (_currentPageIndex.value >= pages.size) {
                 _currentPageIndex.value = pages.size - 1
             }
+            _pages.value = pages
+        }
+    }
+
+    fun togglePageColorMode(id: String) {
+        viewModelScope.launch {
+            val currentColorMode = _pages.value.find { p -> p.id == id }?.colorMode
+            currentColorMode?.let {
+                val newColorMode =
+                    if (it == ColorMode.COLOR) ColorMode.GRAYSCALE else ColorMode.COLOR
+                val pages = withContext(Dispatchers.IO) {
+                    imageRepository.setColorMode(id, newColorMode)
+                    imageRepository.pages()
+                }
+                _pages.value = pages
+            }
         }
     }
 

app/src/main/java/org/fairscan/app/data/DocumentMetadata.kt

@@ -15,6 +15,7 @@
 package org.fairscan.app.data
 
 import kotlinx.serialization.Serializable
+import org.fairscan.imageprocessing.ColorMode
 
 @Serializable
 data class DocumentMetadataV1(
@@ -39,7 +40,8 @@ data class PageV2(
     val baseRotationDegrees: Int = 0,
     val manualRotationDegrees: Int = 0,
     val quad: NormalizedQuad? = null,
-    val isColored: Boolean? = null
+    val isColored: Boolean? = null,
+    val colorMode: ColorMode? = null,
 )
 
 @Serializable

app/src/main/java/org/fairscan/app/data/ImageRepository.kt

@@ -37,7 +37,7 @@ import org.fairscan.imageprocessing.ColorMode
 import org.fairscan.imageprocessing.Point
 import org.fairscan.imageprocessing.Quad
 import java.io.File
-import java.util.Collections
+import java.util.Collections.synchronizedMap
 
 const val SOURCE_DIR_NAME = "sources"
 const val PROCESSED_DIR_NAME = "scanned_pages"
@@ -65,11 +65,12 @@ class ImageRepository(
     private val json = Json { prettyPrint = false; encodeDefaults = true }
     private var pages: PageStore = PageStore(loadPages())
 
+    private val processingJobs = synchronizedMap(mutableMapOf<PageViewKey, Deferred<Unit>>())
     private val imageCache = createLruCache<PageViewKey, Deferred<Jpeg?>>(maxEntries = 50)
     private val thumbnailCache = createLruCache<PageViewKey, Deferred<Jpeg?>>(maxEntries = 200)
 
     private fun <K, V> createLruCache(maxEntries: Int): MutableMap<K, V> =
-        Collections.synchronizedMap(object : LinkedHashMap<K, V>(16, 0.75f, true) {
+        synchronizedMap(object : LinkedHashMap<K, V>(16, 0.75f, true) {
             override fun removeEldestEntry(eldest: Map.Entry<K, V>) = size > maxEntries
         })
 
@@ -91,7 +92,7 @@ class ImageRepository(
         return when {
             metadataPages != null ->
                 metadataPages
-                    .filter { "${it.id}.jpg" in filesOnDisk }
+                    .filter { processedImageFileName(it.id, it.colorMode) in filesOnDisk }
                     .toMutableList()
             else ->
                 filesOnDisk
@@ -135,7 +136,7 @@ class ImageRepository(
         pages.pages().mapNotNull {
             runCatching {
                 val manualRotation = Rotation.fromDegrees(it.manualRotationDegrees)
-                ScanPage(it.id, manualRotation, it.toMetadata())
+                ScanPage(it.id, manualRotation, it.colorMode, it.toMetadata())
             }.getOrNull()
         }
     }
@@ -143,24 +144,53 @@ class ImageRepository(
     suspend fun add(processed: Jpeg, source: Jpeg, metadata: PageMetadata) =
         mutex.withLock {
             val id = "${System.currentTimeMillis()}"
-            val fileName = "$id.jpg"
+            val key = PageViewKey(id, Rotation.R0, metadata.autoColorMode)
-            File(processedDir, fileName).writeBytes(processed.bytes)
+            processedImageFile(key).writeBytes(processed.bytes)
-            File(sourceDir, fileName).writeBytes(source.bytes)
+            sourceFile(id).writeBytes(source.bytes)
             pages.addOrReplace(
                 PageV2(
                     id = id,
                     quad = metadata.normalizedQuad.toSerializable(),
                     baseRotationDegrees = metadata.baseRotation.degrees,
                     manualRotationDegrees = Rotation.R0.degrees,
-                    isColored = metadata.autoColorMode == ColorMode.COLOR
+                    isColored = metadata.autoColorMode == ColorMode.COLOR,
+                    colorMode = metadata.autoColorMode,
                 )
             )
             saveMetadata()
             // Pre-populate cache for R0
-            val key = PageViewKey(id, Rotation.R0)
             imageCache.put(key, CompletableDeferred(processed))
         }
 
+    suspend fun setColorMode(id: String, colorMode: ColorMode) {
+        val key = PageViewKey(id, Rotation.R0, colorMode)
+        val processedFile = processedImageFile(key)
+        val metadata = mutex.withLock { pages.get(id)?.toMetadata() }
+        val sourceFile = sourceFile(id)
+        if (metadata == null || !sourceFile.exists())
+            return
+
+        val job = processingJobs.computeIfAbsent(key) {
+            scope.async(Dispatchers.IO) {
+                if (!processedFile.exists()) {
+                    val sourceJpeg = Jpeg(sourceFile.readBytes())
+                    val processedJpeg = transformations.process(sourceJpeg, metadata, colorMode)
+                    processedFile.writeBytes(processedJpeg.bytes)
+                }
+            }
+        }
+        try {
+            job.await()
+        } finally {
+            processingJobs.remove(key, job)
+        }
+
+        mutex.withLock {
+            pages.update(id) { it.copy(colorMode = colorMode) }
+            saveMetadata()
+        }
+    }
+
     suspend fun rotate(id: String, clockwise: Boolean) = mutex.withLock {
         val page = pages.get(id) ?: return@withLock
         val delta = if (clockwise) Rotation.R90 else Rotation.R270
@@ -198,7 +228,7 @@ class ImageRepository(
 
     private suspend fun computeProcessedImage(key: PageViewKey): Jpeg? =
         withContext(Dispatchers.IO) {
-            val baseFile = File(processedDir, "${key.pageId}.jpg")
+            val baseFile = processedImageFile(key)
             if (!baseFile.exists()) return@withContext null
             val baseJpeg = Jpeg(baseFile.readBytes())
             if (key.rotation == Rotation.R0) {
@@ -220,8 +250,20 @@ class ImageRepository(
 
     // --- Other operations ---
 
+    private fun processedImageFileName(id: String, colorMode: ColorMode?) : String =
+        if (colorMode == null)
+            "${id}.jpg"
+        else
+            "${id}.${colorMode.name.lowercase()}.jpg"
+
+    private fun processedImageFile(key: PageViewKey) : File =
+        File(processedDir, processedImageFileName(key.pageId, key.colorMode))
+
+    private fun sourceFile(id: String): File =
+        File(sourceDir, "$id.jpg")
+
     fun source(id: String): Jpeg? {
-        val file = File(sourceDir, "$id.jpg")
+        val file = sourceFile(id)
         return if (file.exists()) Jpeg(file.readBytes()) else null
     }
 
@@ -233,7 +275,7 @@ class ImageRepository(
     suspend fun delete(id: String) = mutex.withLock {
         pages.delete(id)
         saveMetadata()
-        File(sourceDir, "$id.jpg").delete()
+        sourceFile(id).delete()
         processedDir.listFiles()
             ?.filter { it.name.startsWith("$id.") || it.name.startsWith("$id-") }
             ?.forEach { it.delete() }

app/src/main/java/org/fairscan/app/data/ImageTransformations.kt

@@ -15,6 +15,8 @@
 package org.fairscan.app.data
 
 import org.fairscan.app.domain.Jpeg
+import org.fairscan.app.domain.PageMetadata
+import org.fairscan.imageprocessing.ColorMode
 
 interface ImageTransformations {
 
@@ -22,4 +24,6 @@ interface ImageTransformations {
 
     fun resize(input: Jpeg, maxSize: Int): Jpeg
 
+    fun process(source: Jpeg, metadata: PageMetadata, colorMode: ColorMode): Jpeg
+
 }

app/src/main/java/org/fairscan/app/domain/ExportPreparation.kt

@@ -15,6 +15,7 @@
 package org.fairscan.app.domain
 
 import org.fairscan.app.data.ImageRepository
+import org.fairscan.imageprocessing.ColorMode
 import org.fairscan.imageprocessing.extractDocument
 import org.fairscan.imageprocessing.resizeForMaxPixels
 import org.fairscan.imageprocessing.scaledTo
@@ -48,10 +49,11 @@ suspend fun jpegsForExport(
         ExportQuality.HIGH -> pages.map { page ->
             JpegProvider {
                 val source = imageRepository.source(page.id)
-                val pageMetadata = page.metadata
+                val metadata = page.metadata
                 val manualRotation = page.manualRotation
-                if (source != null && pageMetadata != null)
+                val colorMode = page.colorMode
-                    prepareJpegForHigh(source, pageMetadata, manualRotation, exportQuality)
+                if (source != null && metadata != null && colorMode != null)
+                    prepareJpegForHigh(source, metadata, manualRotation, colorMode, exportQuality)
                 else
                     jpeg(page, imageRepository)
             }
@@ -86,6 +88,7 @@ private fun prepareJpegForHigh(
     source: Jpeg,
     pageMetadata: PageMetadata,
     manualRotation: Rotation,
+    colorMode: ColorMode,
     exportQuality: ExportQuality,
 ): Jpeg {
 
@@ -94,13 +97,8 @@ private fun prepareJpegForHigh(
     try {
         decoded = source.toMat()
         val quad = pageMetadata.normalizedQuad.scaledTo(1, 1, decoded.width(), decoded.height())
-        page = extractDocument(
+        val rotationDegrees = pageMetadata.baseRotation.add(manualRotation).degrees
-            decoded,
+        page = extractDocument(decoded, quad, rotationDegrees, colorMode, exportQuality.maxPixels)
-            quad,
-            pageMetadata.baseRotation.add(manualRotation).degrees,
-            pageMetadata.autoColorMode,
-            exportQuality.maxPixels
-        )
         return Jpeg.fromMat(page, exportQuality.jpegQuality)
     } finally {
         decoded?.release()

app/src/main/java/org/fairscan/app/domain/Page.kt

@@ -26,16 +26,18 @@ data class PageMetadata(
 data class ScanPage(
     val id: String,
     val manualRotation: Rotation,
+    val colorMode: ColorMode?,
     val metadata: PageMetadata?,
 ) {
-    fun key(): PageViewKey = PageViewKey(id, manualRotation)
+    fun key(): PageViewKey = PageViewKey(id, manualRotation, colorMode)
 }
 
 data class PageViewKey(
     val pageId: String,
     val rotation: Rotation,
+    val colorMode: ColorMode?,
 ) {
-    val saveKey: String get() = "$pageId-${rotation.degrees}"
+    val saveKey: String get() = "$pageId-${rotation.degrees}-$colorMode"
 }
 
 enum class Rotation(val degrees: Int) {

app/src/main/java/org/fairscan/app/platform/OpenCvImageTransformations.kt

@@ -15,7 +15,12 @@
 package org.fairscan.app.platform
 
 import org.fairscan.app.data.ImageTransformations
+import org.fairscan.app.domain.ExportQuality
 import org.fairscan.app.domain.Jpeg
+import org.fairscan.app.domain.PageMetadata
+import org.fairscan.imageprocessing.ColorMode
+import org.fairscan.imageprocessing.extractDocument
+import org.fairscan.imageprocessing.scaledTo
 import org.opencv.core.Mat
 import org.opencv.core.Size
 import org.opencv.imgproc.Imgproc
@@ -59,4 +64,30 @@ class OpenCvTransformations : ImageTransformations {
             output?.release()
         }
     }
+
+    override fun process(source: Jpeg, metadata: PageMetadata, colorMode: ColorMode): Jpeg {
+        val exportQuality = ExportQuality.BALANCED
+        var sourceMat: Mat? = null
+        var page: Mat? = null
+        try {
+            sourceMat = source.toMat()
+            val quad = metadata.normalizedQuad.scaledTo(
+                1,
+                1,
+                sourceMat.width(),
+                sourceMat.height()
+            )
+            page = extractDocument(
+                sourceMat,
+                quad,
+                metadata.baseRotation.degrees,
+                colorMode,
+                exportQuality.maxPixels
+            )
+            return Jpeg.fromMat(page, exportQuality.jpegQuality)
+        } finally {
+            sourceMat?.release()
+            page?.release()
+        }
+    }
 }

app/src/main/java/org/fairscan/app/ui/PreviewUtils.kt

@@ -24,6 +24,7 @@ import org.fairscan.app.domain.PageViewKey
 import org.fairscan.app.domain.Rotation
 import org.fairscan.app.ui.state.DocumentUiModel
 import org.fairscan.app.ui.state.PageThumbnail
+import org.fairscan.imageprocessing.ColorMode
 
 fun dummyNavigation(): Navigation {
     return Navigation({}, {}, {}, {}, {}, {}, {}, {})
@@ -35,7 +36,7 @@ fun fakeDocument(): DocumentUiModel {
 
 fun fakeDocument(pageIds: ImmutableList<String>, context: Context): DocumentUiModel {
     val pageKeys = pageIds.map {
-        PageThumbnail(PageViewKey(it, Rotation.R0), fakeImage(it, context))
+        PageThumbnail(PageViewKey(it, Rotation.R0, ColorMode.COLOR), fakeImage(it, context))
     }.toImmutableList()
     return DocumentUiModel(pageKeys)
 }

app/src/main/java/org/fairscan/app/ui/screens/document/DocumentScreen.kt

@@ -31,7 +31,9 @@ import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.lazy.rememberLazyListState
 import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.Contrast
 import androidx.compose.material.icons.filled.Done
+import androidx.compose.material.icons.filled.Palette
 import androidx.compose.material.icons.filled.RotateLeft
 import androidx.compose.material.icons.filled.RotateRight
 import androidx.compose.material.icons.outlined.Add
@@ -74,6 +76,9 @@ import org.fairscan.app.ui.dummyNavigation
 import org.fairscan.app.ui.fakeDocument
 import org.fairscan.app.ui.fakeImage
 import org.fairscan.app.ui.theme.FairScanTheme
+import org.fairscan.imageprocessing.ColorMode
+import org.fairscan.imageprocessing.ColorMode.COLOR
+import org.fairscan.imageprocessing.ColorMode.GRAYSCALE
 
 @OptIn(ExperimentalMaterial3Api::class)
 @Composable
@@ -83,6 +88,7 @@ fun DocumentScreen(
     onExportClick: () -> Unit,
     onDeleteImage: (String) -> Unit,
     onRotateImage: (String, Boolean) -> Unit,
+    onToggleColorMode: (String) -> Unit,
     onPageReorder: (String, Int) -> Unit,
     onPageSelected: (Int) -> Unit,
 ) {
@@ -116,6 +122,7 @@ fun DocumentScreen(
             uiState,
             { showDeletePageDialog.value = true },
             onRotateImage,
+            onToggleColorMode,
             modifier
         )
         if (showDeletePageDialog.value) {
@@ -133,6 +140,7 @@ private fun DocumentPreview(
     uiState: DocumentUiState,
     onDeleteImage: (String) -> Unit,
     onRotateImage: (String, Boolean) -> Unit,
+    onToggleColorMode: (String) -> Unit,
     modifier: Modifier,
 ) {
     val currentPageIndex = uiState.currentPageIndex
@@ -145,7 +153,7 @@ private fun DocumentPreview(
         Box (
             modifier = Modifier.fillMaxSize()
         ) {
-            val bitmap = uiState.currentPageBitmap
+            val bitmap = uiState.currentPage.bitmap
             if (bitmap != null) {
                 val imageBitmap = bitmap.asImageBitmap()
                 val zoomState = remember(imageId) {
@@ -167,6 +175,15 @@ private fun DocumentPreview(
                     )
                 }
             }
+            uiState.currentPage.colorMode?.let {
+                ColorModeButton(
+                    currentColorMode = it,
+                    onToggle = { onToggleColorMode(imageId) },
+                    modifier = Modifier
+                        .align(Alignment.BottomStart)
+                        .padding(8.dp)
+                )
+            }
             RotationButtons(imageId, onRotateImage, Modifier.align(Alignment.BottomCenter))
             SecondaryActionButton(
                 Icons.Outlined.Delete,
@@ -179,10 +196,10 @@ private fun DocumentPreview(
             Text("${currentPageIndex + 1} / ${document.pageCount()}",
                 color = MaterialTheme.colorScheme.inverseOnSurface,
                 modifier = Modifier
-                    .align(Alignment.BottomStart)
+                    .align(Alignment.TopCenter)
                     .padding(all = 16.dp)
                     .background(
-                        color = MaterialTheme.colorScheme.inverseSurface.copy(alpha = 0.5f),
+                        color = MaterialTheme.colorScheme.inverseSurface.copy(alpha = 0.7f),
                         shape = RoundedCornerShape(4.dp)
                     )
                     .padding(horizontal = 8.dp, vertical = 2.dp)
@@ -199,7 +216,7 @@ fun RotationButtons(
 ) {
     // RotateLeft on the left, RotateRight on the right: for both LTR and RTL languages
     CompositionLocalProvider(LocalLayoutDirection provides LayoutDirection.Ltr) {
-        Row(modifier = modifier.padding(4.dp)) {
+        Row(modifier = modifier.padding(8.dp)) {
             // Using AutoMirrored icons would lead to an opposite rotation in RTL languages
             @Suppress("DEPRECATION")
             SecondaryActionButton(
@@ -218,6 +235,32 @@ fun RotationButtons(
     }
 }
 
+@Composable
+fun ColorModeButton(
+    currentColorMode: ColorMode,
+    onToggle: () -> Unit,
+    modifier: Modifier = Modifier
+) {
+    val icon = when (currentColorMode) {
+        COLOR ->  Icons.Default.Palette
+        GRAYSCALE -> Icons.Default.Contrast
+    }
+    val label = when (currentColorMode) {
+        COLOR ->  stringResource(R.string.color_mode_color)
+        GRAYSCALE -> stringResource(R.string.color_mode_grayscale)
+    }
+    Column(
+        horizontalAlignment = Alignment.CenterHorizontally,
+        modifier = modifier
+    ) {
+        SecondaryActionButton(
+            icon = icon,
+            contentDescription = label,
+            onClick = onToggle,
+        )
+    }
+}
+
 @Composable
 private fun BottomBar(
     onExportClick: () -> Unit,
@@ -264,11 +307,12 @@ fun DocumentScreenPreview() {
             LocalContext.current
         )
         DocumentScreen(
-            uiState = DocumentUiState(1, image, document),
+            uiState = DocumentUiState(1, CurrentPageUiState(image, COLOR), document),
             navigation = dummyNavigation(),
             onExportClick = {},
             onDeleteImage = { _ -> },
             onRotateImage = { _,_ -> },
+            onToggleColorMode = { _ -> },
             onPageReorder = { _,_ -> },
             onPageSelected = { _ -> },
         )

app/src/main/java/org/fairscan/app/ui/screens/document/DocumentUiState.kt

@@ -16,9 +16,15 @@ package org.fairscan.app.ui.screens.document
 
 import android.graphics.Bitmap
 import org.fairscan.app.ui.state.DocumentUiModel
+import org.fairscan.imageprocessing.ColorMode
 
 data class DocumentUiState(
     val currentPageIndex: Int,
-    val currentPageBitmap: Bitmap?,
+    val currentPage: CurrentPageUiState,
     val document: DocumentUiModel,
 )
+
+data class CurrentPageUiState(
+    val bitmap: Bitmap? = null,
+    val colorMode: ColorMode? = null,
+)

app/src/main/java/org/fairscan/app/ui/state/DocumentUiModel.kt

@@ -16,10 +16,11 @@ package org.fairscan.app.ui.state
 
 import android.graphics.Bitmap
 import kotlinx.collections.immutable.ImmutableList
+import kotlinx.collections.immutable.persistentListOf
 import org.fairscan.app.domain.PageViewKey
 
 data class DocumentUiModel(
-    val pages: ImmutableList<PageThumbnail>,
+    val pages: ImmutableList<PageThumbnail> = persistentListOf(),
 ) {
     fun pageCount(): Int {
         return pages.size

app/src/main/res/values-ar/strings.xml

@@ -8,6 +8,8 @@
     <string name="cancel">ألغِ</string>
     <string name="change_directory">غيّر المجلد</string>
     <string name="clear_text">امحُ النص</string>
+    <string name="color_mode_color">ألوان</string>
+    <string name="color_mode_grayscale">تدرج الرمادي</string>
     <string name="contact">تواصل</string>
     <string name="copied_logs">نُسخت السجلات إلى الحافظة</string>
     <string name="copy_logs">انسخ السجلات</string>

app/src/main/res/values-cs/strings.xml

@@ -8,6 +8,8 @@
     <string name="cancel">Zrušit</string>
     <string name="change_directory">Změnit složku</string>
     <string name="clear_text">Smazat text</string>
+    <string name="color_mode_color">Barva</string>
+    <string name="color_mode_grayscale">Odstíny šedi</string>
     <string name="contact">Kontakt</string>
     <string name="copied_logs">Protokoly zkopírovány do schránky</string>
     <string name="copy_logs">Kopírovat protokoly</string>

app/src/main/res/values-de/strings.xml

@@ -8,6 +8,8 @@
     <string name="cancel">Abbrechen</string>
     <string name="change_directory">Ordner ändern</string>
     <string name="clear_text">Text löschen</string>
+    <string name="color_mode_color">Farbe</string>
+    <string name="color_mode_grayscale">Graustufen</string>
     <string name="contact">Kontakt</string>
     <string name="copied_logs">Logs in die Zwischenablage kopiert</string>
     <string name="copy_logs">Logs kopieren</string>

app/src/main/res/values-es/strings.xml

@@ -8,6 +8,8 @@
     <string name="cancel">Cancelar</string>
     <string name="change_directory">Cambiar carpeta</string>
     <string name="clear_text">Borrar texto</string>
+    <string name="color_mode_color">Color</string>
+    <string name="color_mode_grayscale">Escala de grises</string>
     <string name="contact">Contacto</string>
     <string name="copied_logs">Registros copiados al portapapeles</string>
     <string name="copy_logs">Copiar registros</string>

app/src/main/res/values-fr/strings.xml

@@ -8,6 +8,8 @@
     <string name="cancel">Annuler</string>
     <string name="change_directory">Changer de dossier</string>
     <string name="clear_text">Effacer le text</string>
+    <string name="color_mode_color">Couleur</string>
+    <string name="color_mode_grayscale">Niveaux de gris</string>
     <string name="contact">Contact</string>
     <string name="copied_logs">Logs copiés dans le presse-papiers</string>
     <string name="copy_logs">Copier les logs</string>

app/src/main/res/values-gl/strings.xml

@@ -8,6 +8,8 @@
     <string name="cancel">Cancelar</string>
     <string name="change_directory">Trocar cartafol</string>
     <string name="clear_text">Borrar texto</string>
+    <string name="color_mode_color">Cor</string>
+    <string name="color_mode_grayscale">Escala de grises</string>
     <string name="contact">Contacto</string>
     <string name="copied_logs">Rexistros copiados ao portapapeis</string>
     <string name="copy_logs">Copiar rexistros</string>

app/src/main/res/values-it/strings.xml

@@ -8,6 +8,8 @@
     <string name="cancel">Annulla</string>
     <string name="change_directory">Cambia cartella</string>
     <string name="clear_text">Svuota testo</string>
+    <string name="color_mode_color">Colore</string>
+    <string name="color_mode_grayscale">Scala di grigi</string>
     <string name="contact">Contatti</string>
     <string name="copied_logs">Log copiati negli appunti</string>
     <string name="copy_logs">Copia log</string>

app/src/main/res/values-pt-rBR/strings.xml

@@ -8,6 +8,8 @@
     <string name="cancel">Cancelar</string>
     <string name="change_directory">Alterar diretório</string>
     <string name="clear_text">Limpar texto</string>
+    <string name="color_mode_color">Cor</string>
+    <string name="color_mode_grayscale">Escala de cinza</string>
     <string name="contact">Contato</string>
     <string name="copied_logs">Registros copiados para a área de transferência</string>
     <string name="copy_logs">Copiar registros</string>

app/src/main/res/values-ru/strings.xml

@@ -8,6 +8,8 @@
     <string name="cancel">Отмена</string>
     <string name="change_directory">Изменить папку</string>
     <string name="clear_text">Стереть текст</string>
+    <string name="color_mode_color">Цвет</string>
+    <string name="color_mode_grayscale">Оттенки серого</string>
     <string name="contact">Контакты</string>
     <string name="copied_logs">Журналы скопированы в буфер обмена</string>
     <string name="copy_logs">Копировать журналы</string>

app/src/main/res/values-tr/strings.xml

@@ -8,6 +8,8 @@
     <string name="cancel">İptal</string>
     <string name="change_directory">Dizini değiştir</string>
     <string name="clear_text">Metni temizle</string>
+    <string name="color_mode_color">Renkli</string>
+    <string name="color_mode_grayscale">Gri tonlama</string>
     <string name="contact">İletişim</string>
     <string name="copied_logs">Günlükler panoya kopyalandı</string>
     <string name="copy_logs">Günlükleri kopyala</string>

app/src/main/res/values-zh-rTW/strings.xml

@@ -8,6 +8,8 @@
     <string name="cancel">取消</string>
     <string name="change_directory">變更目錄</string>
     <string name="clear_text">清除文字</string>
+    <string name="color_mode_color">彩色</string>
+    <string name="color_mode_grayscale">灰階</string>
     <string name="contact">聯絡我們</string>
     <string name="copied_logs">日誌已複製到剪貼簿</string>
     <string name="copy_logs">複製日誌</string>

app/src/main/res/values-zh/strings.xml

@@ -8,6 +8,8 @@
     <string name="cancel">取消</string>
     <string name="change_directory">更改目录</string>
     <string name="clear_text">清除文字</string>
+    <string name="color_mode_color">彩色</string>
+    <string name="color_mode_grayscale">灰度</string>
     <string name="contact">联系人</string>
     <string name="copied_logs">日志已复制到剪贴板</string>
     <string name="copy_logs">复制日志</string>

app/src/main/res/values/strings.xml

@@ -9,6 +9,8 @@
     <string name="cancel">Cancel</string>
     <string name="change_directory">Change folder</string>
     <string name="clear_text">Clear text</string>
+    <string name="color_mode_color">Color</string>
+    <string name="color_mode_grayscale">Grayscale</string>
     <string name="contact">Contact</string>
     <string name="copied_logs">Logs copied to clipboard</string>
     <string name="copy_logs">Copy logs</string>

app/src/test/java/org/fairscan/app/data/ImageRepositoryTest.kt

@@ -27,6 +27,7 @@ import org.fairscan.app.domain.Rotation.R180
 import org.fairscan.app.domain.Rotation.R270
 import org.fairscan.app.domain.Rotation.R90
 import org.fairscan.imageprocessing.ColorMode
+import org.fairscan.imageprocessing.ColorMode.COLOR
 import org.fairscan.imageprocessing.Point
 import org.fairscan.imageprocessing.Quad
 import org.junit.Rule
@@ -44,7 +45,7 @@ class ImageRepositoryTest {
     private val testScope = TestScope()
 
     val quad1 = Quad(Point(.01, .02), Point(.1, .03), Point(.11, .12), Point(.03, .09))
-    val metadata1 = PageMetadata(quad1, R90, ColorMode.COLOR)
+    val metadata1 = PageMetadata(quad1, R90, COLOR)
 
     fun getFilesDir(): File {
         if (_filesDir == null) {
@@ -61,6 +62,10 @@ class ImageRepositoryTest {
             override fun resize(input: Jpeg, maxSize: Int): Jpeg {
                 return jpeg(input.bytes[0])
             }
+
+            override fun process(source: Jpeg, metadata: PageMetadata, colorMode: ColorMode): Jpeg {
+                TODO("Not yet implemented")
+            }
         }
         return ImageRepository(getFilesDir(), transformations, 200, testScope)
     }
@@ -73,7 +78,7 @@ class ImageRepositoryTest {
         repo.add(jpeg, jpeg(51), metadata1)
         assertThat(repo.imageIds()).hasSize(1)
         val id = repo.imageIds()[0]
-        val key = PageViewKey(id, R0)
+        val key = PageViewKey(id, R0, COLOR)
         assertThat(repo.jpegBytes(key)).isEqualTo(jpeg)
         assertThat(repo.getThumbnail(key)?.bytes).isEqualTo(byteArrayOf(101))
 
@@ -140,7 +145,7 @@ class ImageRepositoryTest {
         File(processedDir(), "1-90.jpg").writeBytes(bytes)
         val repo = repo()
         assertThat(repo.imageIds()).containsExactly("1")
-        assertThat(repo.jpegBytes(PageViewKey("1", R0))?.bytes).isEqualTo(bytes)
+        assertThat(repo.jpegBytes(PageViewKey("1", R0, null))?.bytes).isEqualTo(bytes)
     }
 
     @Test
@@ -169,14 +174,14 @@ class ImageRepositoryTest {
         File(processedDir(), "1-90.jpg").writeBytes(bytes)
         val repo = repo()
         assertThat(repo.imageIds()).containsExactly("1")
-        assertThat(repo.jpegBytes(PageViewKey("1", R0))?.bytes).isEqualTo(bytes)
+        assertThat(repo.jpegBytes(PageViewKey("1", R0, null))?.bytes).isEqualTo(bytes)
     }
 
     @Test
     fun `should return null on invalid id`() = runTest {
         val repo = repo()
         assertThat(repo.imageIds()).isEmpty()
-        assertThat(repo.jpegBytes(PageViewKey("x", R0))).isNull()
+        assertThat(repo.jpegBytes(PageViewKey("x", R0, COLOR))).isNull()
     }
 
     @Test
@@ -255,7 +260,7 @@ class ImageRepositoryTest {
             val metadata = PageV2("1", 0, 0, quad, isColored).toMetadata()
             assertThat(metadata).isNotNull()
             assertThat(metadata!!.autoColorMode).isEqualTo(
-                if (isColored) ColorMode.COLOR else ColorMode.GRAYSCALE
+                if (isColored) COLOR else ColorMode.GRAYSCALE
             )
         }
     }