diff --git a/assets/js/controllers/edit_upload.js b/assets/js/controllers/edit_upload.js
index 929b905..f1d472a 100644
--- a/assets/js/controllers/edit_upload.js
+++ b/assets/js/controllers/edit_upload.js
@@ -1,6 +1,10 @@
 import Handlebars from "handlebars";
 import {Controller} from "@hotwired/stimulus";
 
+Handlebars.registerHelper("submit_on", function (id, event) {
+    return `data-action="${event}->edit-upload#updateProcessor" data-edit-upload-id-param="${id}"`
+});
+
 const processorFrame = Handlebars.compile(`
     <div class="card mb-3">
       <div class="card-header d-flex justify-content-between">
@@ -11,7 +15,7 @@ const processorFrame = Handlebars.compile(`
         >X</a>
       </div>
       <div class="card-body">
-        {{{props}}}
+        <form data-role="processor-params" data-params-id="{{id}}">{{{props}}}</form>
       </div>
     </div>
 `);
@@ -19,7 +23,12 @@ const processorFrame = Handlebars.compile(`
 const processorUIs = {
     "shadow": {
         label: "Shadow",
-        template: Handlebars.compile(`This processor has no properties.`),
+        template: Handlebars.compile(`
+            <div class="mb-3">
+              <label for="{{id}}_width" class="form-label">Colour</label>
+              <input name="width" class="form-control" id="{{id}}_{{props.color}}" type="color" value="{{color}}" {{{submit_on id 'change'}}}>
+            </div>
+        `),
     },
     "resize": {
         label: "Resize",
diff --git a/services/imgedit/processing.go b/services/imgedit/processing.go
index 68f8b9d..378ead5 100644
--- a/services/imgedit/processing.go
+++ b/services/imgedit/processing.go
@@ -14,6 +14,34 @@ import (
 	"lmika.dev/lmika/weiro/models"
 )
 
+type imageProcessor struct {
+	newParams    func() any
+	processImage func(ctx context.Context, srcImg image.Image, params any) (image.Image, error)
+}
+
+type shadowProcessorArgs struct {
+	Color   string `json:"color"`
+	OffsetY int    `json:"offset_y"`
+}
+
+var processors = map[string]imageProcessor{
+	"shadow": {
+		newParams: func() any {
+			return &shadowProcessorArgs{
+				Color:   "#000000",
+				OffsetY: 0,
+			}
+		},
+		processImage: func(ctx context.Context, srcImg image.Image, params any) (image.Image, error) {
+			p := params.(*shadowProcessorArgs)
+
+			shadow := makeBoxShadow(srcImg, color.Black, 4, 10, p.OffsetY)
+			composit := imaging.OverlayCenter(shadow, srcImg, 1.0)
+			return composit, nil
+		},
+	},
+}
+
 func (s *Service) reprocess(ctx context.Context, session *models.ImageEditSession) (imageSource, error) {
 	var img imageSource
 
@@ -72,12 +100,22 @@ func (s *Service) processImage(ctx context.Context, srcImg image.Image, processo
 		defer f.Close()
 
 		return imaging.Decode(f)
-	case "shadow":
-		shadow := makeBoxShadow(srcImg, color.Black, 4, 10, 0)
-		composit := imaging.OverlayCenter(shadow, srcImg, 1.0)
-		return composit, nil
+		//case "shadow":
+		//	shadow := makeBoxShadow(srcImg, color.Black, 4, 10, 0)
+		//	composit := imaging.OverlayCenter(shadow, srcImg, 1.0)
+		//	return composit, nil
 	}
-	return nil, fmt.Errorf("unknown processor type: %v", processor.Type)
+
+	proc, ok := processors[processor.Type]
+	if !ok {
+		return nil, fmt.Errorf("unknown processor type: %v", processor.Type)
+	}
+
+	paramType := proc.newParams()
+	if err := json.Unmarshal(processor.Props, paramType); err != nil {
+		return nil, err
+	}
+	return proc.processImage(ctx, srcImg, paramType)
 }
 
 type imageSource interface {
diff --git a/services/imgedit/service.go b/services/imgedit/service.go
index 97603a8..d9f3ba4 100644
--- a/services/imgedit/service.go
+++ b/services/imgedit/service.go
@@ -3,6 +3,7 @@ package imgedit
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"io"
 	"time"
 
@@ -97,10 +98,21 @@ func (s *Service) AddProcessor(ctx context.Context, sessionID string, req AddPro
 		return nil, err
 	}
 
-	// TODO: verify processor, etc.
+	proc, ok := processors[req.Type]
+	if !ok {
+		return nil, fmt.Errorf("unknown processor type: %v", req.Type)
+	}
+
+	paramType := proc.newParams()
+	paramBytes, err := json.Marshal(paramType)
+	if err != nil {
+		return nil, err
+	}
+
 	session.Processors = append(session.Processors, models.ImageEditProcessor{
-		ID:   models.NewNanoID(),
-		Type: req.Type,
+		ID:    models.NewNanoID(),
+		Type:  req.Type,
+		Props: paramBytes,
 	})
 
 	session.RecalcVersionIDs()