Github user HyukjinKwon commented on a diff in the pull request:
https://github.com/apache/spark/pull/19439#discussion_r148429895
--- Diff: mllib/src/main/scala/org/apache/spark/ml/image/ImageSchema.scala
---
@@ -0,0 +1,236 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.ml.image
+
+import java.awt.Color
+import java.awt.color.ColorSpace
+import java.io.ByteArrayInputStream
+import javax.imageio.ImageIO
+
+import scala.collection.JavaConverters._
+
+import org.apache.spark.annotation.{Experimental, Since}
+import org.apache.spark.input.PortableDataStream
+import org.apache.spark.sql.{DataFrame, Row, SparkSession}
+import org.apache.spark.sql.types._
+
+@Experimental
+@Since("2.3.0")
+object ImageSchema {
+
+ val undefinedImageType = "Undefined"
+
+ val imageFields: Array[String] = Array("origin", "height", "width",
"nChannels", "mode", "data")
+
+ val ocvTypes: Map[String, Int] = Map(
+ undefinedImageType -> -1,
+ "CV_8U" -> 0, "CV_8UC1" -> 0, "CV_8UC3" -> 16, "CV_8UC4" -> 24
+ )
+
+ /**
+ * Used for conversion to python
+ */
+ val _ocvTypes: java.util.Map[String, Int] = ocvTypes.asJava
+
+ /**
+ * Schema for the image column: Row(String, Int, Int, Int, Int,
Array[Byte])
+ */
+ val columnSchema = StructType(
+ StructField(imageFields(0), StringType, true) ::
+ StructField(imageFields(1), IntegerType, false) ::
+ StructField(imageFields(2), IntegerType, false) ::
+ StructField(imageFields(3), IntegerType, false) ::
+ // OpenCV-compatible type: CV_8UC3 in most cases
+ StructField(imageFields(4), IntegerType, false) ::
+ // Bytes in OpenCV-compatible order: row-wise BGR in most cases
+ StructField(imageFields(5), BinaryType, false) :: Nil)
+
+ /**
+ * DataFrame with a single column of images named "image" (nullable)
+ */
+ val imageSchema = StructType(StructField("image", columnSchema, true) ::
Nil)
+
+ /**
+ * :: Experimental ::
+ * Gets the origin of the image
+ *
+ * @return The origin of the image
+ */
+ def getOrigin(row: Row): String = row.getString(0)
+
+ /**
+ * :: Experimental ::
+ * Gets the height of the image
+ *
+ * @return The height of the image
+ */
+ def getHeight(row: Row): Int = row.getInt(1)
+
+ /**
+ * :: Experimental ::
+ * Gets the width of the image
+ *
+ * @return The width of the image
+ */
+ def getWidth(row: Row): Int = row.getInt(2)
+
+ /**
+ * :: Experimental ::
+ * Gets the number of channels in the image
+ *
+ * @return The number of channels in the image
+ */
+ def getNChannels(row: Row): Int = row.getInt(3)
+
+ /**
+ * :: Experimental ::
+ * Gets the OpenCV representation as an int
+ *
+ * @return The OpenCV representation as an int
+ */
+ def getMode(row: Row): Int = row.getInt(4)
+
+ /**
+ * :: Experimental ::
+ * Gets the image data
+ *
+ * @return The image data
+ */
+ def getData(row: Row): Array[Byte] = row.getAs[Array[Byte]](5)
+
+ /**
+ * Default values for the invalid image
+ *
+ * @param origin Origin of the invalid image
+ * @return Row with the default values
+ */
+ private def invalidImageRow(origin: String): Row =
+ Row(Row(origin, -1, -1, -1, ocvTypes(undefinedImageType),
Array.ofDim[Byte](0)))
+
+ /**
+ * Convert the compressed image (jpeg, png, etc.) into OpenCV
+ * representation and store it in DataFrame Row
+ *
+ * @param origin Arbitrary string that identifies the image
+ * @param bytes Image bytes (for example, jpeg)
+ * @return DataFrame Row or None (if the decompression fails)
+ */
+ private[spark] def decode(origin: String, bytes: Array[Byte]):
Option[Row] = {
+
+ val img = ImageIO.read(new ByteArrayInputStream(bytes))
+
+ if (img == null) {
+ None
+ } else {
+ val isGray = img.getColorModel.getColorSpace.getType ==
ColorSpace.TYPE_GRAY
+ val hasAlpha = img.getColorModel.hasAlpha
+
+ val height = img.getHeight
+ val width = img.getWidth
+ val (nChannels, mode) = if (isGray) {
+ (1, ocvTypes("CV_8UC1"))
+ } else if (hasAlpha) {
+ (4, ocvTypes("CV_8UC4"))
+ } else {
+ (3, ocvTypes("CV_8UC3"))
+ }
+
+ val imageSize = height * width * nChannels
+ assert(imageSize < 1e9, "image is too large")
+ val decoded = Array.ofDim[Byte](imageSize)
+
+ // Grayscale images in Java require special handling to get the
correct intensity
+ if (isGray) {
+ var offset = 0
+ val raster = img.getRaster
+ for (h <- 0 until height) {
+ for (w <- 0 until width) {
+ decoded(offset) = raster.getSample(w, h, 0).toByte
+ offset += 1
+ }
+ }
+ } else {
+ var offset = 0
+ for (h <- 0 until height) {
+ for (w <- 0 until width) {
+ val color = new Color(img.getRGB(w, h))
+
+ decoded(offset) = color.getBlue.toByte
+ decoded(offset + 1) = color.getGreen.toByte
+ decoded(offset + 2) = color.getRed.toByte
+ if (nChannels == 4) {
+ decoded(offset + 3) = color.getAlpha.toByte
+ }
+ offset += nChannels
+ }
+ }
+ }
+
+ // the internal "Row" is needed, because the image is a single
DataFrame column
+ Some(Row(Row(origin, height, width, nChannels, mode, decoded)))
+ }
+ }
+
+ /**
+ * :: Experimental ::
+ * Read the directory of images from the local or remote source
+ *
+ * @param path Path to the image directory
+ * @param sparkSession Spark Session, if omitted gets or creates the
session
+ * @param recursive Recursive path search flag
+ * @param numPartitions Number of the DataFrame partitions,
+ * if omitted uses defaultParallelism instead
+ * @param dropImageFailures Drop the files that are not valid images
from the result
+ * @param sampleRatio Fraction of the files loaded
+ * @return DataFrame with a single column "image" of images;
+ * see ImageSchema for the details
+ */
+ def readImages(
+ path: String,
+ sparkSession: SparkSession = null,
--- End diff --
BTW, default values do not work in Java API IIRC -
[scala-style-guide#default-parameter-values](https://github.com/databricks/scala-style-guide#default-parameter-values).
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