diff --git a/README.md b/README.md
index 55f22e1..40fa5ec 100644
--- a/README.md
+++ b/README.md
@@ -105,7 +105,7 @@ Authorization: Bearer <Token>
     }
   ],
   "output": {
-    "format": 0,
+    "format": "jpg",
     "quality": 90
   }
 }
@@ -148,13 +148,13 @@ Available pipeline `type`s:  `0` (Image), `1` (Video)
 
 The image pipeline offers the following additional output options.
 
-Available `format` types: `0` (jpeg)    
+Available `format` types: `jpg` (or `jpeg`), `png`, `gif`, `tif` (or `tiff`) and `bmp`      
 The `quality` field can contain any integer between 1 and 100.
 
 ```json
 {
   "output": {
-    "format": 0,
+    "format": "jpg",
     "quality": 90
   }
 }
diff --git a/config/example.json b/config/example.json
index f2c773c..d50cca1 100644
--- a/config/example.json
+++ b/config/example.json
@@ -33,7 +33,7 @@
         }
     ],
     "output": {
-        "format": 0,
+        "format": "jpg",
         "quality": 90
     }
 }
diff --git a/pipelines/pipeline.go b/pipelines/pipeline.go
index c5cc9b8..c13d608 100644
--- a/pipelines/pipeline.go
+++ b/pipelines/pipeline.go
@@ -38,8 +38,8 @@ type Pipeline struct {
 	RemoveMetadata bool         `json:"remove_metadata" faker:"-"`
 	Steps          []Step       `json:"steps" faker:"-"`
 	Output         struct {
-		Format  int `json:"format"`
-		Quality int `json:"quality"`
+		Format  string `json:"format"`
+		Quality int    `json:"quality"`
 	} `json:"output" faker:"-"`
 }
 
@@ -63,7 +63,16 @@ func (p Pipeline) Run(srcPath, bucketName string, storageProvider storage.IStora
 		}
 	}
 
-	format := imaging.Format(p.Output.Format)
+	outputFormat := p.Output.Format
+	if outputFormat == "" {
+		outputFormat = "jpg"
+	}
+
+	format, err := imaging.FormatFromExtension(outputFormat)
+	if err != nil {
+		return "", errors.New(fmt.Sprintf("output format '%s' is not supported", outputFormat))
+	}
+
 	var options []imaging.EncodeOption
 
 	if p.Output.Quality != 0 {
diff --git a/pipelines/pipeline_test.go b/pipelines/pipeline_test.go
index 0b2a20c..63a9f7b 100644
--- a/pipelines/pipeline_test.go
+++ b/pipelines/pipeline_test.go
@@ -362,4 +362,44 @@ func TestEncoding(t *testing.T) {
 		os.Remove(storageProvider.GetPath(Bucket, "source.jpg"))
 		os.Remove(storageProvider.GetPath(Bucket, dest))
 	})
+
+	t.Run("Wrong output format results in error", func(t *testing.T) {
+		const InvalidPayload string = `{
+			"name": "example pipeline",
+			"type": 1,
+			"removeMetadata": false,
+			"steps": [
+				{
+					"name": "resize image",
+					"type": 0,
+					"options": {
+						"width": 1280,
+						"height": 720,
+						"upscale": false
+					}
+				}
+			],
+			"output": {
+				"format": "foo",
+				"quality": 50
+			}
+		}`
+
+		wd, _ := os.Getwd()
+		pipe := DeserializePipelines([][]byte{[]byte(InvalidPayload)})[0]
+
+		storageProvider := storage.GetFileSystemStorageProvider("test", "..")
+
+		// copy test file to storage bucket
+		_, err := storageProvider.StoreExisting(Bucket, "source.jpg", filepath.Join(wd, "../tests/files/900x900.jpg"))
+		assert.Nil(t, err, "Test file should be readable")
+		assert.FileExists(t, storageProvider.GetPath(Bucket, "source.jpg"))
+
+		// run pipeline steps
+		_, err = pipe.Run("source.jpg", Bucket, storageProvider)
+		assert.EqualError(t, err, "output format 'foo' is not supported")
+
+		// clean up
+		os.Remove(storageProvider.GetPath(Bucket, "source.jpg"))
+	})
 }