diff --git a/server/router/fileserver/fileserver.go b/server/router/fileserver/fileserver.go
index bac7a46e1..c49d92e3a 100644
--- a/server/router/fileserver/fileserver.go
+++ b/server/router/fileserver/fileserver.go
@@ -36,6 +36,9 @@ const (
 var SupportedThumbnailMimeTypes = []string{
 	"image/png",
 	"image/jpeg",
+	"image/heic",
+	"image/heif",
+	"image/webp",
 }
 
 // FileServerService handles HTTP file serving with proper range request support.
@@ -143,6 +146,10 @@ func (s *FileServerService) serveAttachmentFile(c echo.Context) error {
 	// Defense-in-depth: prevent embedding in frames and restrict content loading
 	c.Response().Header().Set("X-Frame-Options", "DENY")
 	c.Response().Header().Set("Content-Security-Policy", "default-src 'none'; style-src 'unsafe-inline';")
+	// Support HDR/wide color gamut display for capable browsers
+	if strings.HasPrefix(contentType, "image/") || strings.HasPrefix(contentType, "video/") {
+		c.Response().Header().Set("Color-Gamut", "srgb, p3, rec2020")
+	}
 
 	// Force download for non-media files to prevent XSS execution
 	if !strings.HasPrefix(contentType, "image/") &&
@@ -194,12 +201,15 @@ func (s *FileServerService) serveUserAvatar(c echo.Context) error {
 	}
 
 	// Validate avatar MIME type to prevent XSS
+	// Supports standard formats and HDR-capable formats
 	allowedAvatarTypes := map[string]bool{
 		"image/png":  true,
 		"image/jpeg": true,
 		"image/jpg":  true,
 		"image/gif":  true,
 		"image/webp": true,
+		"image/heic": true,
+		"image/heif": true,
 	}
 	if !allowedAvatarTypes[imageType] {
 		return echo.NewHTTPError(http.StatusBadRequest, "invalid avatar image type")
@@ -336,8 +346,16 @@ func (s *FileServerService) getCurrentUser(ctx context.Context, c echo.Context)
 }
 
 // isImageType checks if the mime type is an image that supports thumbnails.
+// Supports standard formats (PNG, JPEG) and HDR-capable formats (HEIC, HEIF, WebP).
 func (*FileServerService) isImageType(mimeType string) bool {
-	return mimeType == "image/png" || mimeType == "image/jpeg"
+	supportedTypes := map[string]bool{
+		"image/png":  true,
+		"image/jpeg": true,
+		"image/heic": true,
+		"image/heif": true,
+		"image/webp": true,
+	}
+	return supportedTypes[mimeType]
 }
 
 // getAttachmentReader returns a reader for the attachment content.
diff --git a/web/src/components/MemoView/components/metadata/AttachmentCard.tsx b/web/src/components/MemoView/components/metadata/AttachmentCard.tsx
index 2aadfb76c..1fae54fd3 100644
--- a/web/src/components/MemoView/components/metadata/AttachmentCard.tsx
+++ b/web/src/components/MemoView/components/metadata/AttachmentCard.tsx
@@ -1,6 +1,6 @@
 import { cn } from "@/lib/utils";
 import type { Attachment } from "@/types/proto/api/v1/attachment_service_pb";
-import { getAttachmentType, getAttachmentUrl } from "@/utils/attachment";
+import { getAttachmentType, getAttachmentUrl, getColorspace } from "@/utils/attachment";
 
 interface AttachmentCardProps {
   attachment: Attachment;
@@ -11,6 +11,7 @@ interface AttachmentCardProps {
 const AttachmentCard = ({ attachment, onClick, className }: AttachmentCardProps) => {
   const attachmentType = getAttachmentType(attachment);
   const sourceUrl = getAttachmentUrl(attachment);
+  const colorspace = getColorspace(attachment.type);
 
   if (attachmentType === "image/*") {
     return (
@@ -20,12 +21,21 @@ const AttachmentCard = ({ attachment, onClick, className }: AttachmentCardProps)
         className={cn("w-full h-full object-cover rounded-lg cursor-pointer", className)}
         onClick={onClick}
         loading="lazy"
+        {...(colorspace && { colorSpace: colorspace as unknown as string })}
       />
     );
   }
 
   if (attachmentType === "video/*") {
-    return <video src={sourceUrl} className={cn("w-full h-full object-cover rounded-lg", className)} controls preload="metadata" />;
+    return (
+      <video
+        src={sourceUrl}
+        className={cn("w-full h-full object-cover rounded-lg", className)}
+        controls
+        preload="metadata"
+        {...(colorspace && { colorSpace: colorspace as unknown as string })}
+      />
+    );
   }
 
   return null;
diff --git a/web/src/components/MemoView/components/metadata/AttachmentList.tsx b/web/src/components/MemoView/components/metadata/AttachmentList.tsx
index a5b793e1e..522072790 100644
--- a/web/src/components/MemoView/components/metadata/AttachmentList.tsx
+++ b/web/src/components/MemoView/components/metadata/AttachmentList.tsx
@@ -26,18 +26,19 @@ function separateMediaAndDocs(attachments: Attachment[]): { media: Attachment[];
 }
 
 const AttachmentList = ({ attachments }: AttachmentListProps) => {
-  const [previewImage, setPreviewImage] = useState<{ open: boolean; urls: string[]; index: number }>({
+  const [previewImage, setPreviewImage] = useState<{ open: boolean; urls: string[]; index: number; mimeType?: string }>({
     open: false,
     urls: [],
     index: 0,
+    mimeType: undefined,
   });
 
   const handleImageClick = (imgUrl: string, mediaAttachments: Attachment[]) => {
-    const imgUrls = mediaAttachments
-      .filter((attachment) => getAttachmentType(attachment) === "image/*")
-      .map((attachment) => getAttachmentUrl(attachment));
+    const imageAttachments = mediaAttachments.filter((attachment) => getAttachmentType(attachment) === "image/*");
+    const imgUrls = imageAttachments.map((attachment) => getAttachmentUrl(attachment));
     const index = imgUrls.findIndex((url) => url === imgUrl);
-    setPreviewImage({ open: true, urls: imgUrls, index });
+    const mimeType = imageAttachments[index]?.type;
+    setPreviewImage({ open: true, urls: imgUrls, index, mimeType });
   };
 
   const { media: mediaItems, docs: docItems } = separateMediaAndDocs(attachments);
@@ -77,6 +78,7 @@ const AttachmentList = ({ attachments }: AttachmentListProps) => {
         onOpenChange={(open: boolean) => setPreviewImage((prev) => ({ ...prev, open }))}
         imgUrls={previewImage.urls}
         initialIndex={previewImage.index}
+        mimeType={previewImage.mimeType}
       />
     </>
   );
diff --git a/web/src/components/PreviewImageDialog.tsx b/web/src/components/PreviewImageDialog.tsx
index 4787c892e..9bcf424ca 100644
--- a/web/src/components/PreviewImageDialog.tsx
+++ b/web/src/components/PreviewImageDialog.tsx
@@ -2,16 +2,19 @@ import { X } from "lucide-react";
 import React, { useEffect, useState } from "react";
 import { Button } from "@/components/ui/button";
 import { Dialog, DialogContent } from "@/components/ui/dialog";
+import { getColorspace } from "@/utils/attachment";
 
 interface Props {
   open: boolean;
   onOpenChange: (open: boolean) => void;
   imgUrls: string[];
   initialIndex?: number;
+  mimeType?: string; // MIME type for HDR detection
 }
 
-function PreviewImageDialog({ open, onOpenChange, imgUrls, initialIndex = 0 }: Props) {
+function PreviewImageDialog({ open, onOpenChange, imgUrls, initialIndex = 0, mimeType }: Props) {
   const [currentIndex, setCurrentIndex] = useState(initialIndex);
+  const colorspace = mimeType ? getColorspace(mimeType) : undefined;
 
   // Update current index when initialIndex prop changes
   useEffect(() => {
@@ -80,6 +83,7 @@ function PreviewImageDialog({ open, onOpenChange, imgUrls, initialIndex = 0 }: P
             draggable={false}
             loading="eager"
             decoding="async"
+            {...(colorspace && { colorSpace: colorspace as unknown as string })}
           />
         </div>
 
diff --git a/web/src/utils/attachment.ts b/web/src/utils/attachment.ts
index 5f3f1c64e..d78f04cf5 100644
--- a/web/src/utils/attachment.ts
+++ b/web/src/utils/attachment.ts
@@ -52,3 +52,34 @@ export const isMidiFile = (mimeType: string): boolean => {
 const isPSD = (t: string) => {
   return t === "image/vnd.adobe.photoshop" || t === "image/x-photoshop" || t === "image/photoshop";
 };
+
+// HDR-capable MIME types that support wide color gamut
+export const HDR_CAPABLE_FORMATS = [
+  "image/heic",
+  "image/heif",
+  "image/webp",
+  "image/png", // PNG can contain ICC profiles for wide gamut
+  "image/jpeg", // JPEG can support extended color via profiles
+  "video/mp4", // Can contain HDR tracks
+  "video/quicktime", // Can contain HDR tracks
+  "video/x-matroska", // Can contain HDR tracks
+  "video/webm", // VP9 Profile 2 for HDR
+];
+
+// isHDRCapable returns true if the MIME type supports HDR/wide color gamut.
+export const isHDRCapable = (mimeType: string): boolean => {
+  return HDR_CAPABLE_FORMATS.some((format) => mimeType.startsWith(format));
+};
+
+// getColorspace returns the appropriate colorspace attribute for wide gamut images.
+// Returns "display-p3" for HDR-capable formats, undefined for standard images.
+export const getColorspace = (mimeType: string): string | undefined => {
+  return isHDRCapable(mimeType) ? "display-p3" : undefined;
+};
+
+// supportsHDR checks if the browser supports wide color gamut display.
+// Uses CSS.supports() to detect color-gamut capability.
+export const supportsHDR = (): boolean => {
+  if (typeof CSS === "undefined") return false;
+  return CSS.supports("(color-gamut: srgb)") && CSS.supports("(color-gamut: p3)");
+};