Initial implementation of a simple graphics state handler / content stream processor. Multiple changes and fixes in colorspace handling. And more.

pdf/contentstream/contentstream.go

@@ -9,6 +9,7 @@
 package contentstream
 
 import (
+	"bytes"
 	"fmt"
 
 	. "github.com/unidoc/unidoc/pdf/core"
@@ -19,6 +20,38 @@ type ContentStreamOperation struct {
 	Operand string
 }
 
+type ContentStreamOperations []*ContentStreamOperation
+
+// Convert a set of content stream operations to a content stream byte presentation, i.e. the kind that can be
+// stored as a PDF stream or string format.
+func (this ContentStreamOperations) Bytes() []byte {
+	var buf bytes.Buffer
+
+	for _, op := range this {
+		if op == nil {
+			continue
+		}
+
+		if op.Operand == "BI" {
+			// Inline image requires special handling.
+			buf.WriteString(op.Operand + "\n")
+			buf.WriteString(op.Params[0].DefaultWriteString())
+
+		} else {
+			// Default handler.
+			for _, param := range op.Params {
+				buf.WriteString(param.DefaultWriteString())
+				buf.WriteString(" ")
+
+			}
+
+			buf.WriteString(op.Operand + "\n")
+		}
+	}
+
+	return buf.Bytes()
+}
+
 // Parses and extracts all text data in content streams and returns as a string.
 // Does not take into account Encoding table, the output is simply the character codes.
 func (this *ContentStreamParser) ExtractText() (string, error) {

pdf/contentstream/graphics.go

@@ -0,0 +1,557 @@
+package contentstream
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/unidoc/unidoc/common"
+	. "github.com/unidoc/unidoc/pdf/core"
+	. "github.com/unidoc/unidoc/pdf/model"
+)
+
+// Basic graphics state implementation.
+// Initially only implementing and tracking a portion of the information specified.  Easy to add more.
+type GraphicsState struct {
+	ColorspaceStroking    PdfColorspace
+	ColorspaceNonStroking PdfColorspace
+	ColorStroking         PdfColor
+	ColorNonStroking      PdfColor
+}
+
+type GraphicStateStack []GraphicsState
+
+func (gs *GraphicsState) String() string {
+	return fmt.Sprintf("%+v", gs)
+}
+
+func (gsStack *GraphicStateStack) Push(gs GraphicsState) {
+	*gsStack = append(*gsStack, gs)
+}
+
+func (gsStack *GraphicStateStack) Pop() GraphicsState {
+	gs := (*gsStack)[len(*gsStack)-1]
+	*gsStack = (*gsStack)[:len(*gsStack)-1]
+	return gs
+}
+
+// ContentStreamProcessor defines a data structure and methods for processing a content stream, keeping track of the
+// current graphics state, and allowing external handlers to define their own functions as a part of the processing,
+// for example rendering or extracting certain information.
+type ContentStreamProcessor struct {
+	graphicsStack GraphicStateStack
+	operations    []*ContentStreamOperation
+	graphicsState GraphicsState
+
+	handlers     []HandlerEntry
+	currentIndex int
+}
+
+type HandlerFunc func(op *ContentStreamOperation, gs GraphicsState, resources *PdfPageResources) error
+
+type HandlerEntry struct {
+	Condition HandlerConditionEnum
+	Operand   string
+	Handler   HandlerFunc
+}
+
+type HandlerConditionEnum int
+
+func (this HandlerConditionEnum) All() bool {
+	return this == HandlerConditionEnumAllOperands
+}
+
+func (this HandlerConditionEnum) Operand() bool {
+	return this == HandlerConditionEnumOperand
+}
+
+const (
+	HandlerConditionEnumOperand     HandlerConditionEnum = iota
+	HandlerConditionEnumAllOperands HandlerConditionEnum = iota
+)
+
+func NewContentStreamProcessor(ops []*ContentStreamOperation) *ContentStreamProcessor {
+	csp := ContentStreamProcessor{}
+	csp.graphicsStack = GraphicStateStack{}
+
+	// Set defaults..
+	gs := GraphicsState{}
+
+	csp.graphicsState = gs
+
+	csp.handlers = []HandlerEntry{}
+	csp.currentIndex = 0
+	csp.operations = ops
+
+	return &csp
+}
+
+func (csp *ContentStreamProcessor) AddHandler(condition HandlerConditionEnum, operand string, handler HandlerFunc) {
+	entry := HandlerEntry{}
+	entry.Condition = condition
+	entry.Operand = operand
+	entry.Handler = handler
+	csp.handlers = append(csp.handlers, entry)
+}
+
+func (csp *ContentStreamProcessor) getColorspace(name string, resources *PdfPageResources) (PdfColorspace, error) {
+	switch name {
+	case "DeviceGray":
+		return NewPdfColorspaceDeviceGray(), nil
+	case "DeviceRGB":
+		return NewPdfColorspaceDeviceRGB(), nil
+	case "DeviceCMYK":
+		return NewPdfColorspaceDeviceCMYK(), nil
+	case "Pattern":
+		return NewPdfColorspaceSpecialPattern(), nil
+	}
+
+	// Next check the colorspace dictionary.
+	cs, has := resources.ColorSpace.Colorspaces[name]
+	if has {
+		return cs, nil
+	}
+
+	// Lastly check other potential colormaps.
+	switch name {
+	case "CalGray":
+		return NewPdfColorspaceCalGray(), nil
+	case "CalRGB":
+		return NewPdfColorspaceCalRGB(), nil
+	case "Lab":
+		return NewPdfColorspaceLab(), nil
+	}
+
+	// Otherwise unsupported.
+	common.Log.Debug("Unknown colorspace requested: %s", name)
+	return nil, errors.New("Unsupported colorspace")
+}
+
+// Get initial color for a given colorspace.
+func (csp *ContentStreamProcessor) getInitialColor(cs PdfColorspace) (PdfColor, error) {
+	switch cs := cs.(type) {
+	case *PdfColorspaceDeviceGray:
+		return NewPdfColorDeviceGray(0.0), nil
+	case *PdfColorspaceDeviceRGB:
+		return NewPdfColorDeviceRGB(0.0, 0.0, 0.0), nil
+	case *PdfColorspaceDeviceCMYK:
+		return NewPdfColorDeviceCMYK(0.0, 0.0, 0.0, 1.0), nil
+	case *PdfColorspaceLab:
+		l := 0.0
+		a := 0.0
+		b := 0.0
+		if cs.Range[0] > 0 {
+			l = cs.Range[0]
+		}
+		if cs.Range[2] > 0 {
+			a = cs.Range[2]
+		}
+		return NewPdfColorLab(l, a, b), nil
+	case *PdfColorspaceICCBased:
+		if cs.Alternate == nil {
+			return nil, errors.New("Alternate space not defined for ICC")
+		}
+		return csp.getInitialColor(cs.Alternate)
+	case *PdfColorspaceSpecialIndexed:
+		if cs.Base == nil {
+			return nil, errors.New("Indexed base not specified")
+		}
+		return csp.getInitialColor(cs.Base)
+	case *PdfColorspaceSpecialSeparation:
+		if cs.AlternateSpace == nil {
+			return nil, errors.New("Alternate space not specified")
+		}
+		return csp.getInitialColor(cs.AlternateSpace)
+	case *PdfColorspaceDeviceN:
+		if cs.AlternateSpace == nil {
+			return nil, errors.New("Alternate space not specified")
+		}
+		return csp.getInitialColor(cs.AlternateSpace)
+	case *PdfColorspaceSpecialPattern:
+		// TODO: Define color for pattern space.
+		return nil, errors.New("Initial color for pattern space undefined")
+	}
+
+	common.Log.Debug("Unable to determine initial color for unknown colorspace: %T", cs)
+	return nil, errors.New("Unsupported colorspace")
+}
+
+// Process the entire operations.
+func (this *ContentStreamProcessor) Process(resources *PdfPageResources) error {
+	// Initialize graphics state
+	this.graphicsState.ColorspaceStroking = NewPdfColorspaceDeviceGray()
+	this.graphicsState.ColorspaceNonStroking = NewPdfColorspaceDeviceGray()
+	this.graphicsState.ColorStroking = NewPdfColorDeviceGray(0)
+	this.graphicsState.ColorNonStroking = NewPdfColorDeviceGray(0)
+
+	for _, op := range this.operations {
+		// Internal handling.
+		switch op.Operand {
+		case "q":
+			this.graphicsStack.Push(this.graphicsState)
+		case "Q":
+			this.graphicsState = this.graphicsStack.Pop()
+
+		// Color operations (Table 74 p. 179)
+		case "CS":
+			err := this.handleCommand_CS(op, resources)
+			if err != nil {
+				return err
+			}
+		case "cs":
+			err := this.handleCommand_cs(op, resources)
+			if err != nil {
+				return err
+			}
+		case "SC":
+			err := this.handleCommand_SC(op, resources)
+			if err != nil {
+				return err
+			}
+		case "SCN":
+			err := this.handleCommand_SCN(op, resources)
+			if err != nil {
+				return err
+			}
+		case "sc":
+			err := this.handleCommand_sc(op, resources)
+			if err != nil {
+				return err
+			}
+		case "scn":
+			err := this.handleCommand_scn(op, resources)
+			if err != nil {
+				return err
+			}
+		case "G":
+			err := this.handleCommand_G(op, resources)
+			if err != nil {
+				return err
+			}
+		case "g":
+			err := this.handleCommand_g(op, resources)
+			if err != nil {
+				return err
+			}
+		case "RG":
+			err := this.handleCommand_RG(op, resources)
+			if err != nil {
+				return err
+			}
+		case "rg":
+			err := this.handleCommand_rg(op, resources)
+			if err != nil {
+				return err
+			}
+		case "K":
+			err := this.handleCommand_K(op, resources)
+			if err != nil {
+				return err
+			}
+		case "k":
+			err := this.handleCommand_k(op, resources)
+			if err != nil {
+				return err
+			}
+		}
+
+		// Check if have external handler also, and process if so.
+		for _, entry := range this.handlers {
+			var err error
+			if entry.Condition.All() {
+				err = entry.Handler(op, this.graphicsState, resources)
+			} else if entry.Condition.Operand() && op.Operand == entry.Operand {
+				err = entry.Handler(op, this.graphicsState, resources)
+			}
+			if err != nil {
+				common.Log.Debug("Processor handler error: %v", err)
+				return err
+			}
+		}
+	}
+
+	return nil
+}
+
+// CS: Set the current color space for stroking operations.
+func (csp *ContentStreamProcessor) handleCommand_CS(op *ContentStreamOperation, resources *PdfPageResources) error {
+	if len(op.Params) < 1 {
+		common.Log.Debug("Invalid cs command, skipping over")
+		return errors.New("Too few parameters")
+	}
+	if len(op.Params) > 1 {
+		common.Log.Debug("cs command with too many parameters - continuing")
+		return errors.New("Too many parameters")
+	}
+	name, ok := op.Params[0].(*PdfObjectName)
+	if !ok {
+		common.Log.Debug("ERROR: cs command with invalid parameter, skipping over")
+		return errors.New("Type check error")
+	}
+	// Set the current color space to use for stroking operations.
+	// Either device based or referring to resource dict.
+	cs, err := csp.getColorspace(string(*name), resources)
+	if err != nil {
+		return err
+	}
+	csp.graphicsState.ColorspaceStroking = cs
+
+	// Set initial color.
+	color, err := csp.getInitialColor(cs)
+	if err != nil {
+		return err
+	}
+	csp.graphicsState.ColorStroking = color
+
+	return nil
+}
+
+// cs: Set the current color space for non-stroking operations.
+func (csp *ContentStreamProcessor) handleCommand_cs(op *ContentStreamOperation, resources *PdfPageResources) error {
+	if len(op.Params) < 1 {
+		common.Log.Debug("Invalid CS command, skipping over")
+		return errors.New("Too few parameters")
+	}
+	if len(op.Params) > 1 {
+		common.Log.Debug("CS command with too many parameters - continuing")
+		return errors.New("Too many parameters")
+	}
+	name, ok := op.Params[0].(*PdfObjectName)
+	if !ok {
+		common.Log.Debug("ERROR: CS command with invalid parameter, skipping over")
+		return errors.New("Type check error")
+	}
+	// Set the current color space to use for non-stroking operations.
+	// Either device based or referring to resource dict.
+	cs, err := csp.getColorspace(string(*name), resources)
+	if err != nil {
+		return err
+	}
+	csp.graphicsState.ColorspaceNonStroking = cs
+
+	// Set initial color.
+	color, err := csp.getInitialColor(cs)
+	if err != nil {
+		return err
+	}
+	csp.graphicsState.ColorNonStroking = color
+
+	return nil
+}
+
+// SC: Set the color to use for stroking operations in a device, CIE-based or Indexed colorspace. (not ICC based)
+func (this *ContentStreamProcessor) handleCommand_SC(op *ContentStreamOperation, resources *PdfPageResources) error {
+	// For DeviceGray, CalGray, Indexed: one operand is required
+	// For DeviceRGB, CalRGB, Lab: 3 operands required
+
+	cs := this.graphicsState.ColorspaceStroking
+	if len(op.Params) != cs.GetNumComponents() {
+		common.Log.Debug("Invalid number of parameters for SC")
+		common.Log.Debug("Number %d not matching colorspace %T", len(op.Params), cs)
+		return errors.New("Invalid number of parameters")
+	}
+
+	color, err := cs.ColorFromPdfObjects(op.Params)
+	if err != nil {
+		return err
+	}
+
+	this.graphicsState.ColorStroking = color
+
+	return nil
+}
+
+// SCN: Same as SC but also supports Pattern, Separation, DeviceN and ICCBased color spaces.
+func (this *ContentStreamProcessor) handleCommand_SCN(op *ContentStreamOperation, resources *PdfPageResources) error {
+	cs := this.graphicsState.ColorspaceStroking
+
+	if _, isPattern := cs.(*PdfColorspaceSpecialPattern); isPattern {
+		// TODO handle pattern space spearately. See p. 180.
+		common.Log.Debug("Pattern not handled yet")
+		// Return error?
+		return errors.New("SCN - pattern not handled yet")
+	}
+
+	if len(op.Params) != this.graphicsState.ColorspaceStroking.GetNumComponents() {
+		common.Log.Debug("Invalid number of parameters for SC")
+		common.Log.Debug("Number %d not matching colorspace %T", len(op.Params), cs)
+		return errors.New("Invalid number of parameters")
+	}
+
+	color, err := cs.ColorFromPdfObjects(op.Params)
+	if err != nil {
+		return err
+	}
+
+	this.graphicsState.ColorStroking = color
+
+	return nil
+}
+
+// sc: Same as SC except used for non-stroking operations.
+func (this *ContentStreamProcessor) handleCommand_sc(op *ContentStreamOperation, resources *PdfPageResources) error {
+	cs := this.graphicsState.ColorspaceNonStroking
+	if len(op.Params) != cs.GetNumComponents() {
+		common.Log.Debug("Invalid number of parameters for SC")
+		common.Log.Debug("Number %d not matching colorspace %T", len(op.Params), cs)
+		return errors.New("Invalid number of parameters")
+	}
+
+	color, err := cs.ColorFromPdfObjects(op.Params)
+	if err != nil {
+		return err
+	}
+
+	this.graphicsState.ColorNonStroking = color
+
+	return nil
+}
+
+// scn: Same as SCN except used for non-stroking operations.
+func (this *ContentStreamProcessor) handleCommand_scn(op *ContentStreamOperation, resources *PdfPageResources) error {
+	cs := this.graphicsState.ColorspaceNonStroking
+
+	if _, isPattern := cs.(*PdfColorspaceSpecialPattern); isPattern {
+		// TODO handle pattern space spearately. See p. 180.
+		common.Log.Debug("Pattern not handled yet")
+		return errors.New("SCN - pattern not handled yet")
+	}
+
+	if len(op.Params) != cs.GetNumComponents() {
+		common.Log.Debug("Invalid number of parameters for SC")
+		common.Log.Debug("Number %d not matching colorspace %T", len(op.Params), cs)
+		return errors.New("Invalid number of parameters")
+	}
+
+	color, err := cs.ColorFromPdfObjects(op.Params)
+	if err != nil {
+		return err
+	}
+
+	this.graphicsState.ColorNonStroking = color
+
+	return nil
+}
+
+// G: Set the stroking colorspace to DeviceGray, and the color to the specified graylevel (range [0-1]).
+// gray G
+func (this *ContentStreamProcessor) handleCommand_G(op *ContentStreamOperation, resources *PdfPageResources) error {
+	cs := NewPdfColorspaceDeviceGray()
+	if len(op.Params) != cs.GetNumComponents() {
+		common.Log.Debug("Invalid number of parameters for SC")
+		common.Log.Debug("Number %d not matching colorspace %T", len(op.Params), cs)
+		return errors.New("Invalid number of parameters")
+	}
+
+	color, err := cs.ColorFromPdfObjects(op.Params)
+	if err != nil {
+		return err
+	}
+
+	this.graphicsState.ColorspaceStroking = cs
+	this.graphicsState.ColorStroking = color
+
+	return nil
+}
+
+// g: Same as G, but for non-stroking colorspace and color (range [0-1]).
+// gray g
+func (this *ContentStreamProcessor) handleCommand_g(op *ContentStreamOperation, resources *PdfPageResources) error {
+	cs := NewPdfColorspaceDeviceGray()
+	if len(op.Params) != cs.GetNumComponents() {
+		common.Log.Debug("Invalid number of parameters for SC")
+		common.Log.Debug("Number %d not matching colorspace %T", len(op.Params), cs)
+		return errors.New("Invalid number of parameters")
+	}
+
+	color, err := cs.ColorFromPdfObjects(op.Params)
+	if err != nil {
+		return err
+	}
+
+	this.graphicsState.ColorspaceNonStroking = cs
+	this.graphicsState.ColorNonStroking = color
+
+	return nil
+}
+
+// RG: Sets the stroking colorspace to DeviceRGB and the stroking color to r,g,b. [0-1] ranges.
+// r g b RG
+func (this *ContentStreamProcessor) handleCommand_RG(op *ContentStreamOperation, resources *PdfPageResources) error {
+	cs := NewPdfColorspaceDeviceRGB()
+	if len(op.Params) != cs.GetNumComponents() {
+		common.Log.Debug("Invalid number of parameters for SC")
+		common.Log.Debug("Number %d not matching colorspace %T", len(op.Params), cs)
+		return errors.New("Invalid number of parameters")
+	}
+
+	color, err := cs.ColorFromPdfObjects(op.Params)
+	if err != nil {
+		return err
+	}
+
+	this.graphicsState.ColorspaceStroking = cs
+	this.graphicsState.ColorStroking = color
+
+	return nil
+}
+
+// rg: Same as RG but for non-stroking colorspace, color.
+func (this *ContentStreamProcessor) handleCommand_rg(op *ContentStreamOperation, resources *PdfPageResources) error {
+	cs := NewPdfColorspaceDeviceRGB()
+	if len(op.Params) != cs.GetNumComponents() {
+		common.Log.Debug("Invalid number of parameters for SC")
+		common.Log.Debug("Number %d not matching colorspace %T", len(op.Params), cs)
+		return errors.New("Invalid number of parameters")
+	}
+
+	color, err := cs.ColorFromPdfObjects(op.Params)
+	if err != nil {
+		return err
+	}
+
+	this.graphicsState.ColorspaceNonStroking = cs
+	this.graphicsState.ColorNonStroking = color
+
+	return nil
+}
+
+// K: Sets the stroking colorspace to DeviceCMYK and the stroking color to c,m,y,k. [0-1] ranges.
+// c m y k K
+func (this *ContentStreamProcessor) handleCommand_K(op *ContentStreamOperation, resources *PdfPageResources) error {
+	cs := NewPdfColorspaceDeviceCMYK()
+	if len(op.Params) != cs.GetNumComponents() {
+		common.Log.Debug("Invalid number of parameters for SC")
+		common.Log.Debug("Number %d not matching colorspace %T", len(op.Params), cs)
+		return errors.New("Invalid number of parameters")
+	}
+
+	color, err := cs.ColorFromPdfObjects(op.Params)
+	if err != nil {
+		return err
+	}
+
+	this.graphicsState.ColorspaceStroking = cs
+	this.graphicsState.ColorStroking = color
+
+	return nil
+}
+
+// k: Same as K but for non-stroking colorspace, color.
+func (this *ContentStreamProcessor) handleCommand_k(op *ContentStreamOperation, resources *PdfPageResources) error {
+	cs := NewPdfColorspaceDeviceCMYK()
+	if len(op.Params) != cs.GetNumComponents() {
+		common.Log.Debug("Invalid number of parameters for SC")
+		common.Log.Debug("Number %d not matching colorspace %T", len(op.Params), cs)
+		return errors.New("Invalid number of parameters")
+	}
+
+	color, err := cs.ColorFromPdfObjects(op.Params)
+	if err != nil {
+		return err
+	}
+
+	this.graphicsState.ColorspaceNonStroking = cs
+	this.graphicsState.ColorNonStroking = color
+
+	return nil
+}

pdf/contentstream/inline-image.go

@@ -31,6 +31,42 @@ type ContentStreamInlineImage struct {
 	stream           []byte
 }
 
+// Make a new content stream inline image object from an image.
+func NewInlineImageFromImage(img Image, encoder StreamEncoder) (*ContentStreamInlineImage, error) {
+	if encoder == nil {
+		encoder = NewRawEncoder()
+	}
+
+	inlineImage := ContentStreamInlineImage{}
+	if img.ColorComponents == 1 {
+		inlineImage.ColorSpace = MakeName("DeviceGray")
+	} else if img.ColorComponents == 3 {
+		inlineImage.ColorSpace = MakeName("DeviceRGB")
+	} else if img.ColorComponents == 4 {
+		inlineImage.ColorSpace = MakeName("DeviceCMYK")
+	} else {
+		common.Log.Debug("Invalid number of color components for inline image: %d", img.ColorComponents)
+		return nil, errors.New("Invalid number of color components")
+	}
+	inlineImage.BitsPerComponent = MakeInteger(img.BitsPerComponent)
+	inlineImage.Width = MakeInteger(img.Width)
+	inlineImage.Height = MakeInteger(img.Height)
+
+	encoded, err := encoder.EncodeBytes(img.Data)
+	if err != nil {
+		return nil, err
+	}
+
+	inlineImage.stream = encoded
+	filterName := encoder.GetFilterName()
+	if len(filterName) > 0 {
+		inlineImage.Filter = MakeName(filterName)
+	}
+	// XXX/FIXME: Add decode params?
+
+	return &inlineImage, nil
+}
+
 func (this *ContentStreamInlineImage) String() string {
 	s := fmt.Sprintf("InlineImage(len=%d)\n", len(this.stream))
 	if this.BitsPerComponent != nil {
@@ -107,6 +143,7 @@ func (this *ContentStreamInlineImage) DefaultWriteString() string {
 
 	output.WriteString("ID ")
 	output.Write(this.stream)
+	output.WriteString("\n")
 
 	return output.String()
 }

pdf/contentstream/parser.go

@@ -27,18 +27,17 @@ type ContentStreamParser struct {
 // stream string.
 func NewContentStreamParser(contentStr string) *ContentStreamParser {
 	// Each command has parameters and an operand (command).
-
 	parser := ContentStreamParser{}
 
-	buffer := bytes.NewBufferString(contentStr)
+	buffer := bytes.NewBufferString(contentStr + "\n") // Add newline at end to get last operand without EOF error.
 	parser.reader = bufio.NewReader(buffer)
 
 	return &parser
 }
 
 // Parses all commands in content stream, returning a list of operation data.
-func (this *ContentStreamParser) Parse() ([]*ContentStreamOperation, error) {
+func (this *ContentStreamParser) Parse() (ContentStreamOperations, error) {
-	operations := []*ContentStreamOperation{}
+	operations := ContentStreamOperations{}
 
 	for {
 		operation := ContentStreamOperation{}

pdf/core/encoding.go

@@ -704,6 +704,7 @@ type DCTEncoder struct {
 	BitsPerComponent int // 8 or 16 bit
 	Width            int
 	Height           int
+	Quality          int
 }
 
 // Make a new DCT encoder with default parameters.
@@ -713,6 +714,8 @@ func NewDCTEncoder() *DCTEncoder {
 	encoder.ColorComponents = 3
 	encoder.BitsPerComponent = 8
 
+	encoder.Quality = 75
+
 	return encoder
 }
 
@@ -796,6 +799,7 @@ func newDCTEncoderFromStream(streamObj *PdfObjectStream, multiEnc *MultiEncoder)
 	encoder.Width = cfg.Width
 	encoder.Height = cfg.Height
 	common.Log.Trace("DCT Encoder: %+v", encoder)
+	encoder.Quality = 75
 
 	return encoder, nil
 }
@@ -987,10 +991,12 @@ func (this *DCTEncoder) EncodeBytes(data []byte) ([]byte, error) {
 		}
 	}
 
-	// Use full quality. N.B. even 100 is lossy, as still is transformed, but as good as it gets for DCT.
+	// The quality is specified from 0-100 (with 100 being the best quality) in the DCT structure.
-	// TODO: Add option to override the quality, can be used in compression.
+	// N.B. even 100 is lossy, as still is transformed, but as good as it gets for DCT.
+	// This is not related to the DPI, but rather inherent transformation losses.
+
 	opt := jpeg.Options{}
-	opt.Quality = 100
+	opt.Quality = this.Quality
 
 	var buf bytes.Buffer
 	err := jpeg.Encode(&buf, img, &opt)

pdf/model/page.go

@@ -947,6 +947,20 @@ func (r *PdfPageResources) GetXObjectByName(keyName string) (*PdfObjectStream, X
 	}
 }
 
+func (r *PdfPageResources) setXObjectByName(keyName string, stream *PdfObjectStream) error {
+	if r.XObject == nil {
+		r.XObject = &PdfObjectDictionary{}
+	}
+
+	xresDict, has := r.XObject.(*PdfObjectDictionary)
+	if !has {
+		return errors.New("Type check error")
+	}
+
+	(*xresDict)[PdfObjectName(keyName)] = stream
+	return nil
+}
+
 func (r *PdfPageResources) GetXObjectImageByName(keyName string) (*XObjectImage, error) {
 	stream, xtype := r.GetXObjectByName(keyName)
 	if stream == nil {
@@ -964,6 +978,12 @@ func (r *PdfPageResources) GetXObjectImageByName(keyName string) (*XObjectImage,
 	return ximg, nil
 }
 
+func (r *PdfPageResources) SetXObjectImageByName(keyName string, ximg *XObjectImage) error {
+	stream := ximg.ToPdfObject().(*PdfObjectStream)
+	err := r.setXObjectByName(keyName, stream)
+	return err
+}
+
 func (r *PdfPageResources) GetXObjectFormByName(keyName string) (*XObjectForm, error) {
 	stream, xtype := r.GetXObjectByName(keyName)
 	if stream == nil {
@@ -980,3 +1000,9 @@ func (r *PdfPageResources) GetXObjectFormByName(keyName string) (*XObjectForm, e
 
 	return xform, nil
 }
+
+func (r *PdfPageResources) SetXObjectFormByName(keyName string, xform *XObjectForm) error {
+	stream := xform.ToPdfObject().(*PdfObjectStream)
+	err := r.setXObjectByName(keyName, stream)
+	return err
+}

pdf/model/utils.go

@@ -28,6 +28,20 @@ func getNumberAsFloat(obj PdfObject) (float64, error) {
 	return 0, errors.New("Not a number")
 }
 
+// Convert a list of pdf objects representing floats or integers to a slice of float64 values.
+func getNumbersAsFloat(objects []PdfObject) ([]float64, error) {
+	floats := []float64{}
+	for _, obj := range objects {
+		val, err := getNumberAsFloat(obj)
+		if err != nil {
+			return nil, err
+		}
+		floats = append(floats, val)
+
+	}
+	return floats, nil
+}
+
 // Cases where expecting an integer, but some implementations actually
 // store the number in a floating point format.
 func getNumberAsInt64(obj PdfObject) (int64, error) {

pdf/model/xobject.go

@@ -147,6 +147,23 @@ func (xform *XObjectForm) GetContentStream() ([]byte, error) {
 	return decoded, nil
 }
 
+// Update the content stream, encode if needed.
+func (xform *XObjectForm) SetContentStream(content []byte) error {
+	encoded := content
+	if xform.Filter != nil {
+		enc, err := xform.Filter.EncodeBytes(encoded)
+		if err != nil {
+			return err
+		}
+		encoded = enc
+	}
+
+	xform.primitive.Stream = encoded
+	xform.primitive.PdfObjectDictionary.Set("Length", MakeInteger(int64(len(encoded))))
+
+	return nil
+}
+
 // Return a stream object.
 func (xform *XObjectForm) ToPdfObject() PdfObject {
 	stream := xform.primitive
@@ -221,7 +238,7 @@ func NewXObjectImage() *XObjectImage {
 
 // Creates a new XObject Image from an image object with default
 // options.
-func NewXObjectImageFromImage(name PdfObjectName, img *Image) (*XObjectImage, error) {
+func NewXObjectImageFromImage(name PdfObjectName, img *Image, cs PdfColorspace) (*XObjectImage, error) {
 	xobj := NewXObjectImage()
 
 	xobj.Name = &name
@@ -236,10 +253,21 @@ func NewXObjectImageFromImage(name PdfObjectName, img *Image) (*XObjectImage, er
 	// Bits.
 	xobj.BitsPerComponent = &img.BitsPerComponent
 
-	//xobj.ColorSpace = MakeName("DeviceRGB")
+	// Guess colorspace if not explicitly set.
+	if cs == nil {
+		if img.ColorComponents == 1 {
+			xobj.ColorSpace = NewPdfColorspaceDeviceGray()
+		} else if img.ColorComponents == 3 {
 			xobj.ColorSpace = NewPdfColorspaceDeviceRGB()
+		} else if img.ColorComponents == 4 {
+			xobj.ColorSpace = NewPdfColorspaceDeviceCMYK()
+		} else {
+			return nil, errors.New("Colorspace undefined")
+		}
+	} else {
+		xobj.ColorSpace = cs
 
-	// define color space?
+	}
 
 	return xobj, nil
 }
@@ -350,6 +378,38 @@ func NewXObjectImageFromStream(stream *PdfObjectStream) (*XObjectImage, error) {
 	return img, nil
 }
 
+// Update XObject Image with new image data.
+func (ximg *XObjectImage) SetImage(img *Image, cs PdfColorspace) error {
+	encoded, err := ximg.Filter.EncodeBytes(img.Data)
+	if err != nil {
+		return err
+	}
+
+	ximg.Stream = encoded
+
+	// Width, height and bits.
+	ximg.Width = &img.Width
+	ximg.Height = &img.Height
+	ximg.BitsPerComponent = &img.BitsPerComponent
+
+	// Guess colorspace if not explicitly set.
+	if cs == nil {
+		if img.ColorComponents == 1 {
+			ximg.ColorSpace = NewPdfColorspaceDeviceGray()
+		} else if img.ColorComponents == 3 {
+			ximg.ColorSpace = NewPdfColorspaceDeviceRGB()
+		} else if img.ColorComponents == 4 {
+			ximg.ColorSpace = NewPdfColorspaceDeviceCMYK()
+		} else {
+			return errors.New("Colorspace undefined")
+		}
+	} else {
+		ximg.ColorSpace = cs
+	}
+
+	return nil
+}
+
 // Compress with default settings, updating the underlying stream also.
 // XXX/TODO: Add flate encoding as an option (although lossy).  Need to be able
 // to set default settings and override.