Converting PDF Pages to JPEG Images with PDFium VCL in Delphi

Converting PDF pages to images is essential for thumbnails, previews, and web display. The PDF to JPG demo shows how to render PDF pages as high-quality JPEG images using PDFium VCL.

Overview

This demo converts PDF pages to JPEG images with customizable DPI, quality settings, and page selection. It’s perfect for generating thumbnails, creating image-based archives, or preparing PDFs for web display.

Key Features

Customizable DPI – Control output resolution (72-600 DPI)
Quality Settings – Adjust JPEG compression quality
Page Selection – Convert all pages or specific page ranges
Output Directory – Choose where to save converted images
Progress Tracking – Visual feedback during conversion
Cancellation Support – Cancel long conversions anytime

PDFium DLL Requirements

Before running any PDFium VCL application, ensure the PDFium DLL files are installed:

pdfium32.dll / pdfium64.dll – Standard versions (~5-6 MB)
pdfium32v8.dll / pdfium64v8.dll – With V8 JavaScript engine (~23-27 MB)

Installation: Run PDFiumVCL\DLLs\CopyDlls.bat as Administrator to automatically copy the DLLs to Windows system directories.

Basic PDF to Image Conversion

procedure ConvertPdfToImages;
var
  Pdf: TPdf;
  I: Integer;
  Bitmap: TBitmap;
  JpegImage: TJpegImage;
  Dpi: Integer;
begin
  Dpi := 150; // 150 DPI is good for screen viewing
  
  Pdf := TPdf.Create(nil);
  try
    Pdf.FileName := 'document.pdf';
    Pdf.Active := True;
    
    for I := 1 to Pdf.PageCount do
    begin
      Pdf.PageNumber := I;
      
      // Calculate size based on DPI
      // PDF default is 72 DPI, so scale accordingly
      Bitmap := Pdf.RenderPage(
        0, 0,
        Round(Pdf.PageWidth * Dpi / 72),
        Round(Pdf.PageHeight * Dpi / 72),
        ro0,      // No rotation
        [],       // Default render options
        clWhite   // Background color
      );
      
      try
        // Convert to JPEG
        JpegImage := TJpegImage.Create;
        try
          JpegImage.Assign(Bitmap);
          JpegImage.CompressionQuality := 85;
          JpegImage.SaveToFile(Format('page_%03d.jpg', [I]));
        finally
          JpegImage.Free;
        end;
      finally
        Bitmap.Free;
      end;
    end;
    
  finally
    Pdf.Active := False;
    Pdf.Free;
  end;
end;

procedure ConvertPdfToImages;

var

Pdf: TPdf;

I: Integer;

Bitmap: TBitmap;

JpegImage: TJpegImage;

Dpi: Integer;

begin

Dpi := 150; // 150 DPI is good for screen viewing

Pdf := TPdf.Create(nil);

try

Pdf.FileName := 'document.pdf';

Pdf.Active := True;

for I := 1 to Pdf.PageCount do

begin

Pdf.PageNumber := I;

// Calculate size based on DPI

// PDF default is 72 DPI, so scale accordingly

Bitmap := Pdf.RenderPage(

0, 0,

Round(Pdf.PageWidth * Dpi / 72),

Round(Pdf.PageHeight * Dpi / 72),

ro0, // No rotation

[], // Default render options

clWhite // Background color

);

try

// Convert to JPEG

JpegImage := TJpegImage.Create;

try

JpegImage.Assign(Bitmap);

JpegImage.CompressionQuality := 85;

JpegImage.SaveToFile(Format('page_%03d.jpg', [I]));

finally

JpegImage.Free;

end;

finally

Bitmap.Free;

end;

finally

Pdf.Active := False;

Pdf.Free;

end;

Complete Conversion with Options

procedure TFormMain.ButtonConvertClick(Sender: TObject);
var
  I: Integer;
  OutDir, BaseName, FileName: string;
  JpegImage: TJpegImage;
  Bitmap: TBitmap;
  Dpi, Quality: Integer;
  Pages: TIntArray;
  PageDigits: Integer;
  UseAllPages: Boolean;
begin
  ProgressBar.Position := 0;
  FCancelRequested := False;
  Screen.Cursor := crHourGlass;
  
  try
    try
      if not FileExists(EditPdfFile.Text) then
        raise Exception.Create('PDF file does not exist.');
        
      // Parse settings
      Dpi := StrToIntDef(Trim(EditDPI.Text), 150);
      if Dpi &lt;= 0 then Dpi := 150;
      if Dpi &gt; 600 then Dpi := 600;
      
      Quality := StrToIntDef(Trim(EditQuality.Text), 85);
      if Quality &lt; 1 then Quality := 1;
      if Quality &gt; 100 then Quality := 100;
      
      // Load PDF
      Pdf.FileName := EditPdfFile.Text;
      Pdf.Active := True;
      
      // Parse page ranges
      UseAllPages := Trim(EditPageRange.Text) = '';
      if UseAllPages then
      begin
        SetLength(Pages, Pdf.PageCount);
        for I := 1 to Pdf.PageCount do
          Pages[I - 1] := I;
      end
      else
      begin
        if not ParsePageRanges(EditPageRange.Text, Pdf.PageCount, Pages) then
          raise Exception.Create('Invalid page range.');
      end;
      
      ProgressBar.Max := Length(Pages);
      PageDigits := Length(IntToStr(Pdf.PageCount));
      
      // Setup output
      OutDir := EnsureOutputDir(Pdf.FileName, EditOutputDir.Text);
      BaseName := ChangeFileExt(ExtractFileName(Pdf.FileName), '');
      
      JpegImage := TJpegImage.Create;
      try
        for I := 0 to High(Pages) do
        begin
          if FCancelRequested then
            Break;
            
          Pdf.PageNumber := Pages[I];
          
          // Render page to bitmap
          Bitmap := Pdf.RenderPage(
            0, 0,
            Round(Pdf.PageWidth * Dpi / 72),
            Round(Pdf.PageHeight * Dpi / 72),
            ro0, [], clWhite
          );
          
          try
            // Save as JPEG
            FileName := Format('%s\%s_%.*d.jpg',
              [OutDir, BaseName, PageDigits, Pages[I]]);
              
            JpegImage.Assign(Bitmap);
            JpegImage.CompressionQuality := Quality;
            JpegImage.SaveToFile(FileName);
          finally
            Bitmap.Free;
          end;
          
          ProgressBar.Position := I + 1;
          Application.ProcessMessages;
        end;
      finally
        JpegImage.Free;
      end;
      
    except
      on E: Exception do
        Application.MessageBox(
          PChar('Conversion failed: ' + E.Message),
          'Error', MB_ICONERROR or MB_OK);
    end;
    
  finally
    Screen.Cursor := crDefault;
    Pdf.Active := False;
  end;
end;

100

101

102

procedure TFormMain.ButtonConvertClick(Sender: TObject);

var

I: Integer;

OutDir, BaseName, FileName: string;

JpegImage: TJpegImage;

Bitmap: TBitmap;

Dpi, Quality: Integer;

Pages: TIntArray;

PageDigits: Integer;

UseAllPages: Boolean;

begin

ProgressBar.Position := 0;

FCancelRequested := False;

Screen.Cursor := crHourGlass;

try

if not FileExists(EditPdfFile.Text) then

raise Exception.Create('PDF file does not exist.');

// Parse settings

Dpi := StrToIntDef(Trim(EditDPI.Text), 150);

if Dpi <= 0 then Dpi := 150;

if Dpi > 600 then Dpi := 600;

Quality := StrToIntDef(Trim(EditQuality.Text), 85);

if Quality < 1 then Quality := 1;

if Quality > 100 then Quality := 100;

// Load PDF

Pdf.FileName := EditPdfFile.Text;

Pdf.Active := True;

// Parse page ranges

UseAllPages := Trim(EditPageRange.Text) = '';

if UseAllPages then

begin

SetLength(Pages, Pdf.PageCount);

for I := 1 to Pdf.PageCount do

Pages[I - 1] := I;

end

else

begin

if not ParsePageRanges(EditPageRange.Text, Pdf.PageCount, Pages) then

raise Exception.Create('Invalid page range.');

end;

ProgressBar.Max := Length(Pages);

PageDigits := Length(IntToStr(Pdf.PageCount));

// Setup output

OutDir := EnsureOutputDir(Pdf.FileName, EditOutputDir.Text);

BaseName := ChangeFileExt(ExtractFileName(Pdf.FileName), '');

JpegImage := TJpegImage.Create;

try

for I := 0 to High(Pages) do

begin

if FCancelRequested then

Break;

Pdf.PageNumber := Pages[I];

// Render page to bitmap

Bitmap := Pdf.RenderPage(

0, 0,

Round(Pdf.PageWidth * Dpi / 72),

Round(Pdf.PageHeight * Dpi / 72),

ro0, [], clWhite

);

try

// Save as JPEG

FileName := Format('%s\%s_%.*d.jpg',

[OutDir, BaseName, PageDigits, Pages[I]]);

JpegImage.Assign(Bitmap);

JpegImage.CompressionQuality := Quality;

JpegImage.SaveToFile(FileName);

finally

Bitmap.Free;

end;

ProgressBar.Position := I + 1;

Application.ProcessMessages;

end;

finally

JpegImage.Free;

end;

except

on E: Exception do

Application.MessageBox(

PChar('Conversion failed: ' + E.Message),

'Error', MB_ICONERROR or MB_OK);

end;

finally

Screen.Cursor := crDefault;

Pdf.Active := False;

end;

Understanding RenderPage

The RenderPage method is the key to PDF-to-image conversion:

// Render to a new bitmap
function TPdf.RenderPage(
  Left, Top, Width, Height: Integer;
  Rotation: TRotation = ro0;
  Options: TRenderOptions = [];
  Color: TColor = clWhite
): TBitmap;

// Render to an existing bitmap
procedure TPdf.RenderPage(
  Bitmap: TBitmap;
  Left, Top, Width, Height: Integer;
  Rotation: TRotation = ro0;
  Options: TRenderOptions = [];
  Color: TColor = clWhite
);

// Render directly to a device context (for printing)
procedure TPdf.RenderPage(
  DeviceContext: HDC;
  Left, Top, Width, Height: Integer;
  Rotation: TRotation = ro0;
  Options: TRenderOptions = []
);

// Render to a new bitmap

function TPdf.RenderPage(

Left, Top, Width, Height: Integer;

Rotation: TRotation = ro0;

Options: TRenderOptions = [];

Color: TColor = clWhite

): TBitmap;

// Render to an existing bitmap

procedure TPdf.RenderPage(

Bitmap: TBitmap;

Left, Top, Width, Height: Integer;

Rotation: TRotation = ro0;

Options: TRenderOptions = [];

Color: TColor = clWhite

);

// Render directly to a device context (for printing)

procedure TPdf.RenderPage(

DeviceContext: HDC;

Left, Top, Width, Height: Integer;

Rotation: TRotation = ro0;

Options: TRenderOptions = []

);

Render Options

type
  TRenderOption = (
    reAnnotations,       // Include annotations in output
    reLcd,               // Optimize for LCD displays
    reNoNativeText,      // Don't use system text rendering
    reGrayscale,         // Output in grayscale
    reLimitCache,        // Limit memory cache
    reHalftone,          // Better image downscaling
    rePrinting,          // Optimize for printing
    reNoSmoothText,      // Disable text anti-aliasing
    reNoSmoothImage,     // Disable image anti-aliasing
    reNoSmoothPath       // Disable path anti-aliasing
  );

// Example: High-quality output with annotations
Bitmap := Pdf.RenderPage(0, 0, Width, Height, ro0,
  [reAnnotations, reLcd], clWhite);
  
// Example: Fast, grayscale thumbnail
Bitmap := Pdf.RenderPage(0, 0, 200, 280, ro0,
  [reGrayscale, reNoSmoothText, reNoSmoothImage], clWhite);

type

TRenderOption = (

reAnnotations, // Include annotations in output

reLcd, // Optimize for LCD displays

reNoNativeText, // Don't use system text rendering

reGrayscale, // Output in grayscale

reLimitCache, // Limit memory cache

reHalftone, // Better image downscaling

rePrinting, // Optimize for printing

reNoSmoothText, // Disable text anti-aliasing

reNoSmoothImage, // Disable image anti-aliasing

reNoSmoothPath // Disable path anti-aliasing

);

// Example: High-quality output with annotations

Bitmap := Pdf.RenderPage(0, 0, Width, Height, ro0,

[reAnnotations, reLcd], clWhite);

// Example: Fast, grayscale thumbnail

Bitmap := Pdf.RenderPage(0, 0, 200, 280, ro0,

[reGrayscale, reNoSmoothText, reNoSmoothImage], clWhite);

DPI and Quality Guidelines

Use Case	Recommended DPI	JPEG Quality
Thumbnails	72	60-70
Screen viewing	96-150	80-85
High-quality display	200-300	85-95
Printing	300-600	90-100

Parsing Page Ranges

function TFormMain.ParsePageRanges(const S: string; MaxPage: Integer;
  out Pages: TIntArray): Boolean;
var
  List: TStringList;
  I, A, B, J: Integer;
  Part: string;
  DashPos: Integer;
  Used: array of Boolean;
  Count: Integer;
begin
  Result := False;
  SetLength(Pages, 0);
  
  if Trim(S) = '' then
  begin
    Result := True;
    Exit;
  end;
  
  SetLength(Used, MaxPage + 1);
  for I := 0 to High(Used) do
    Used[I] := False;
    
  List := TStringList.Create;
  try
    List.Delimiter := ',';
    List.DelimitedText := StringReplace(Trim(S), ' ', '', [rfReplaceAll]);
    
    for I := 0 to List.Count - 1 do
    begin
      Part := Trim(List[I]);
      DashPos := Pos('-', Part);
      
      if DashPos &gt; 0 then
      begin
        // Range: "1-5"
        A := StrToIntDef(Trim(Copy(Part, 1, DashPos - 1)), 0);
        B := StrToIntDef(Trim(Copy(Part, DashPos + 1, Length(Part))), 0);
        
        if (A &lt; 1) or (B &lt; A) or (B &gt; MaxPage) then
          Exit;
          
        for J := A to B do
          Used[J] := True;
      end
      else
      begin
        // Single page
        A := StrToIntDef(Part, 0);
        if (A &lt; 1) or (A &gt; MaxPage) then
          Exit;
        Used[A] := True;
      end;
    end;
  finally
    List.Free;
  end;
  
  // Build result array
  Count := 0;
  for I := 1 to MaxPage do
    if Used[I] then Inc(Count);
    
  SetLength(Pages, Count);
  J := 0;
  for I := 1 to MaxPage do
    if Used[I] then
    begin
      Pages[J] := I;
      Inc(J);
    end;
    
  Result := True;
end;

function TFormMain.ParsePageRanges(const S: string; MaxPage: Integer;

out Pages: TIntArray): Boolean;

var

List: TStringList;

I, A, B, J: Integer;

Part: string;

DashPos: Integer;

Used: array of Boolean;

Count: Integer;

begin

Result := False;

SetLength(Pages, 0);

if Trim(S) = '' then

begin

Result := True;

Exit;

end;

SetLength(Used, MaxPage + 1);

for I := 0 to High(Used) do

Used[I] := False;

List := TStringList.Create;

try

List.Delimiter := ',';

List.DelimitedText := StringReplace(Trim(S), ' ', '', [rfReplaceAll]);

for I := 0 to List.Count - 1 do

begin

Part := Trim(List[I]);

DashPos := Pos('-', Part);

if DashPos > 0 then

begin

// Range: "1-5"

A := StrToIntDef(Trim(Copy(Part, 1, DashPos - 1)), 0);

B := StrToIntDef(Trim(Copy(Part, DashPos + 1, Length(Part))), 0);

if (A < 1) or (B < A) or (B > MaxPage) then

Exit;

for J := A to B do

Used[J] := True;

end

else

begin

// Single page

A := StrToIntDef(Part, 0);

if (A < 1) or (A > MaxPage) then

Exit;

Used[A] := True;

end;

finally

List.Free;

end;

// Build result array

Count := 0;

for I := 1 to MaxPage do

if Used[I] then Inc(Count);

SetLength(Pages, Count);

J := 0;

for I := 1 to MaxPage do

if Used[I] then

begin

Pages[J] := I;

Inc(J);

end;

Result := True;

end;

Creating Thumbnails

function CreateThumbnail(Pdf: TPdf; PageNumber: Integer;
  MaxWidth, MaxHeight: Integer): TBitmap;
var
  PageWidth, PageHeight: Double;
  Scale: Double;
  ThumbWidth, ThumbHeight: Integer;
begin
  Pdf.PageNumber := PageNumber;
  
  PageWidth := Pdf.PageWidth;
  PageHeight := Pdf.PageHeight;
  
  // Calculate scale to fit in max dimensions
  Scale := Min(MaxWidth / PageWidth, MaxHeight / PageHeight);
  
  ThumbWidth := Round(PageWidth * Scale);
  ThumbHeight := Round(PageHeight * Scale);
  
  Result := Pdf.RenderPage(0, 0, ThumbWidth, ThumbHeight,
    ro0, [reGrayscale], clWhite);
end;

function CreateThumbnail(Pdf: TPdf; PageNumber: Integer;

MaxWidth, MaxHeight: Integer): TBitmap;

var

PageWidth, PageHeight: Double;

Scale: Double;

ThumbWidth, ThumbHeight: Integer;

begin

Pdf.PageNumber := PageNumber;

PageWidth := Pdf.PageWidth;

PageHeight := Pdf.PageHeight;

// Calculate scale to fit in max dimensions

Scale := Min(MaxWidth / PageWidth, MaxHeight / PageHeight);

ThumbWidth := Round(PageWidth * Scale);

ThumbHeight := Round(PageHeight * Scale);

Result := Pdf.RenderPage(0, 0, ThumbWidth, ThumbHeight,

ro0, [reGrayscale], clWhite);

end;

Use Cases

Thumbnail Generation – Create previews for document browsers
Web Publishing – Convert PDFs to images for web display
Social Media – Share PDF content as images
Archive Conversion – Convert PDF archives to image formats
OCR Preprocessing – Prepare PDFs for OCR processing

Conclusion

The PDF to JPG demo shows how easy it is to convert PDF pages to high-quality images with PDFium VCL. The RenderPage method gives you full control over resolution, quality, and rendering options.

Whether you’re building a thumbnail generator, web publisher, or document converter, PDFium VCL provides the rendering capabilities you need.

Start converting PDFs to images with PDFium VCL Component today.