Image extration support in extractor package. Implements #317 .

pdf/extractor/image.go

@@ -0,0 +1,209 @@
+/*
+ * This file is subject to the terms and conditions defined in
+ * file 'LICENSE.md', which is part of this source code package.
+ */
+
+package extractor
+
+import (
+	"github.com/unidoc/unidoc/common"
+	"github.com/unidoc/unidoc/pdf/contentstream"
+	"github.com/unidoc/unidoc/pdf/core"
+	"github.com/unidoc/unidoc/pdf/model"
+)
+
+// ExtractPageImages returns the image contents of the page extractor, including data
+// and position, size information for each image.
+func (e *Extractor) ExtractPageImages() (*PageImages, error) {
+	ctx := &imageExtractContext{}
+
+	err := ctx.extractImagesInContentStream(e.contents, e.resources)
+	if err != nil {
+		return nil, err
+	}
+
+	images := &PageImages{
+		Images: ctx.extractedImages,
+	}
+	return images, nil
+}
+
+// PageImages represents extracted images on a PDF page with spatial information:
+// display position and size.
+type PageImages struct {
+	Images []ImageMark
+}
+
+// ImageMark represents an image drawn on a page and its position in device coordinates.
+// All coordinates are in device coordinates.
+type ImageMark struct {
+	Image *model.Image
+
+	// Dimensions of the image as displayed in the PDF.
+	Width  float64
+	Height float64
+
+	// Position of the image in PDF coordinates (lower left corner).
+	X float64
+	Y float64
+
+	// Angle if rotated.
+	Angle float64
+}
+
+// Provide context for image extraction content stream processing.
+type imageExtractContext struct {
+	extractedImages []ImageMark
+	inlineImages    int
+	xObjectImages   int
+	xObjectForms    int
+
+	// Cache to avoid processing same objects many times.
+	processedXObjects map[string]bool
+}
+
+func (ctx *imageExtractContext) extractImagesInContentStream(contents string, resources *model.PdfPageResources) error {
+	cstreamParser := contentstream.NewContentStreamParser(contents)
+	operations, err := cstreamParser.Parse()
+	if err != nil {
+		return err
+	}
+
+	ctx.processedXObjects = map[string]bool{}
+
+	processor := contentstream.NewContentStreamProcessor(*operations)
+	processor.AddHandler(contentstream.HandlerConditionEnumAllOperands, "",
+		func(op *contentstream.ContentStreamOperation, gs contentstream.GraphicsState, resources *model.PdfPageResources) error {
+			return ctx.processOperand(op, gs, resources)
+		})
+
+	err = processor.Process(resources)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// Process individual content stream operands for image extraction.
+func (ctx *imageExtractContext) processOperand(op *contentstream.ContentStreamOperation, gs contentstream.GraphicsState, resources *model.PdfPageResources) error {
+	if op.Operand == "BI" && len(op.Params) == 1 {
+		// BI: Inline image.
+
+		iimg, ok := op.Params[0].(*contentstream.ContentStreamInlineImage)
+		if !ok {
+			return nil
+		}
+
+		img, err := iimg.ToImage(resources)
+		if err != nil {
+			return err
+		}
+
+		cs, err := iimg.GetColorSpace(resources)
+		if err != nil {
+			return err
+		}
+		if cs == nil {
+			// Default if not specified?
+			cs = model.NewPdfColorspaceDeviceGray()
+		}
+
+		rgbImg, err := cs.ImageToRGB(*img)
+		if err != nil {
+			return err
+		}
+		xDim := gs.CTM.ScalingFactorX()
+		yDim := gs.CTM.ScalingFactorY()
+		xPos, yPos := gs.CTM.Translation()
+		angle := gs.CTM.Angle()
+
+		imgMark := ImageMark{
+			Image:  &rgbImg,
+			X:      xPos,
+			Y:      yPos,
+			Width:  xDim,
+			Height: yDim,
+			Angle:  angle,
+		}
+
+		ctx.extractedImages = append(ctx.extractedImages, imgMark)
+		ctx.inlineImages++
+	} else if op.Operand == "Do" && len(op.Params) == 1 {
+		// Do: XObject.
+		name, ok := core.GetName(op.Params[0])
+		if !ok {
+			return errTypeCheck
+		}
+
+		// Only process each one once.
+		_, has := ctx.processedXObjects[string(*name)]
+		if has {
+			// Already processed.
+			return nil
+		}
+		ctx.processedXObjects[string(*name)] = true
+
+		_, xtype := resources.GetXObjectByName(*name)
+		if xtype == model.XObjectTypeImage {
+			common.Log.Debug(" XObject Image: %s", *name)
+
+			ximg, err := resources.GetXObjectImageByName(*name)
+			if err != nil {
+				return err
+			}
+
+			img, err := ximg.ToImage()
+			if err != nil {
+				return err
+			}
+
+			common.Log.Debug("@Do CTM: %s", gs.CTM.String())
+			xDim := gs.CTM.ScalingFactorX()
+			yDim := gs.CTM.ScalingFactorY()
+			xPos, yPos := gs.CTM.Translation()
+			angle := gs.CTM.Angle()
+
+			rgbImg, err := ximg.ColorSpace.ImageToRGB(*img)
+			if err != nil {
+				return err
+			}
+			imgMark := ImageMark{
+				Image:  &rgbImg,
+				X:      xPos,
+				Y:      yPos,
+				Width:  xDim,
+				Height: yDim,
+				Angle:  angle,
+			}
+
+			ctx.extractedImages = append(ctx.extractedImages, imgMark)
+			ctx.xObjectImages++
+		} else if xtype == model.XObjectTypeForm {
+			// Go through the XObject Form content stream.
+			xform, err := resources.GetXObjectFormByName(*name)
+			if err != nil {
+				return err
+			}
+
+			formContent, err := xform.GetContentStream()
+			if err != nil {
+				return err
+			}
+
+			// Process the content stream in the Form object too:
+			formResources := xform.Resources
+			if formResources == nil {
+				formResources = resources
+			}
+
+			// Process the content stream in the Form object too:
+			err = ctx.extractImagesInContentStream(string(formContent), formResources)
+			if err != nil {
+				return err
+			}
+			ctx.xObjectForms++
+		}
+	}
+	return nil
+}