fcl-image

Introduction

FCL-Image started life as "fpimage", pretty much as an attempt to implement a generally portable TImage like class, without the deep win32 and VCL ties.

Current file list

The central units are fpimage and fpcanvas and these are further enhanced by OOP derivation.

bmpcomn A few structures and constants for the BMP fileformat
clipping Some utility routines that help with clipping and intersecting of rects.
ellipses Drawing of ellipses and arcs, and filling ellipses and pies.
- TEllipseInfo
extinterpolation interpolation filters for TFPCanvas.StretchDraw (
- TBlackmanInterpolation
- TBlackmanSincInterpolation
- TBlackmanBesselInterpolation
- TGaussianInterpolation
- TBoxInterpolation
- THermiteInterpolation
- TLanczosInterpolation
- TQuadraticInterpolation
- TCubicInterpolation
- TCatromInterpolation
- TBilineairInterpolation
- THanningInterpolation
- THammingInterpolation
fpcanvas Generic Canvas classes.
- TFPCanvasException
- TFPPenException
- TFPBrushException
- TFPFontException
- TFPCustomCanvas
- TFPCanvasHelper
- TFPCustomFont
- TFPCustomFontClass
- TFPCustomPen
- TFPCustomPenClass
- TFPCustomBrush
- TFPCustomBrushClass
- TFPCustomInterpolation
- TFPBaseInterpolation
- TMitchelInterpolation
- TFPCustomCanvas
- TFPCustomDrawFont
- TFPEmptyFont
- TFPCustomDrawPen
- TFPEmptyPen
- TFPCustomDrawBrush
- TFPEmptyBrush
fpcolhash an implementation of a color hash table.
- TFPColorHashException
- TFPColorHashTable
fpditherer contains classes used to dither images.
- FPDithererException
- TFPBaseDitherer
- TFPFloydSteinbergDitherer
fpimage fpImage base definitions and classes
- TFPCustomImageReader
- TFPCustomImageWriter
- TFPCustomImage
- FPImageException
- TFPPalette
- TFPCustomImage
- TFPMemoryImage
- TFPCustomImageHandler
- TFPCustomImageReader
- TFPCustomImageWriter
- TIHData
- TImageHandlersManager
fpimgcanv Image Canvas - canvas which draws on an image.
- TFPImageCanvas
fpimgcmn Image Common: small procedural Helpers (swap,crc)
fppixlcanv
- TPixelCanvas
fpquantizer classes used to quantize images. See [1]
freetype Encapsulating classes over freetype
freetypeh Freetype header translation
ftfont More freetype related font classes
pcxcomn PCX fileformat records and types
pixtools Pixel drawing routines.
pngcomn PNG fileformat records and types
pscanvas TPostScriptCanvas implementation.
targacmn Targa fileformat records and types

Readers and writers for various image formats reside in dedicated units:

fpreadbmp, fpwritebmp: Reader and writer units for .bmp files
fpreadjpeg, fpwritejpeg: Reader and writer units for .jpeg/.jpg files
fpreadpcx, fprwritepcs: Reader and writer units for .pcx files
fpreadpng, fpwritepng: Reader and writer units for .png files
fpreadpnm, fpwritepnm: Reader and writer units for .pnm files
fpreadtga, fpwritetga: Reader and writer units for .tga files
fpreadtiff, fpwritetiff: Reader and writer units for .tiff/.tif files
fpreadxpm, fpwritexpm: Reader and writer units for .xpm files

INC files uses in fpcanvas

fpbrush
fpcanvas
fpcdrawh
fpfont
fphelper
fpinterpolation
fppen

INC files uses in fpmake

fpcolors
fpimage
fphandler
fpcolcnv
fppalette

Demos

drawing
imgconv

Known Issues and limitations

fcl-image is written for maximal portability and maintainability and is quite slow. The main storage type is 16-bit RGBA, storing always 64-bit per pixel, and a function is called to get each pixel.
pngwriter doesn't implement automatic detection of filters, and thus is always "filter none"
most writers don't autodetect what format to save. You must correctly set the relevant writer options ( see also bug 17621).
the color format can be counter intuitive, read this thread
png only implements basic chunk types (idat,trns,plte,ihdr and iend). It e.g. can't handle chunks like pHYs,iCCP,gAMA,cHRM yet. (bug 19209).

Image formats

Here is a table with the correct class to use for each image format, as well as comparing to the LCL.

Format	fcl-image reader unit	fcl-image writer unit	LCL class
Windows Bitmap. A very simple format, usually used without compression and without transparency, but it may also have them, although many applications don't support those extra features. (*.bmp)	fpreadbmp	fpwritebmp	TBitmap
A popular format for websites. It supports up to 8 bits per pixels, which are 256 distinct colors chosen from the 24-bit RGB color space. This limitation makes it unsuitable for complex images, but useful for simple graphics. The image is compressed without loss in quality and the format also supports animations. (*.gif)	fpreadgif	-	TGIFImage
The most popular format for websites, and an ISO standard since 1994. The format compressed the image but generates a small loss of quality. (.jpeg, .jpg)	fpreadjpeg	fpwritejpeg	TJpegImage
A format widely used in DOS applications, but now less popular. (*.pcx)	fpreadpcx	fpwritepcx	-
Portable Network Graphics. A popular format for it's efficient compression without quality loss. (*.png)	fpreadpng	fpwritepng	TPortableNetworkGraphic
Supports the formats Portable BitMaps (.pbm), Portable GrayMaps (.pgm) and Portable PixMaps (*.ppm)	fpreadpnm	fpwritepnm	TPortableAnyMapGraphic
The default file format for Adobe Photoshop® (*.psd)	fpreadpsd	-	-
Called either Truevision TGA File Format or TARGA File Format, this is a compressed format commonly used in games. (.tga, .tpic)	fpreadtga	fpwritetga	-
Tagged Image File Format (TIFF), originally created to have a common image format for scanners. (.tiff, .tif). Controlled by Adobe®	fpreadtiff	fpwritetiff	TTiffImage
X PixMap, an image format used by the X Window System which stores the data in ASCII text. Is also used as an icon format in UNIX applications. (*.xpm)	fpreadxpm	fpwritexpm	TPixmap
X Window Dump file format. Used by the program xwd which generates screenshots in the X Window System. (*.xwd)	fpreadxwd	-	-
Windows Icon. Is a list of small bitmaps in various color depths and sizes, with transparency support and no compression. (*.ico)	-	-	TIcon
Windows Cursor. Exactly the same format as the Windows Icon, but with an extra field in the header for the cursor hotspot. (*.cur)	-	-	TCursorImage
macOS icon. List of small images in various sizes. (*.icns)	-	-	TIcnsIcon

Tiff

Working features of the reader:

Black and white/lineart/1 bit (FPC trunk only, not in FPC 2.6.x)
Grayscale 8,16bit (optional alpha),
RGB 8,16bit (optional alpha),
Orientation, except for rotated orientation
compression: packbits, LZW, deflate
endian
multiple images/multipage
strips and tiles
Sets properties in the image Extras properties, which is used by the writer, so that reading/writing keeps many common tags like Artist, Copyright, DateAndTime, HostComputer, ImageDescription, Maker, Model, Software, DocumentName, XResolution, YResolution, Orientation, bit depts, page name, isThumbnail.

Here is an incomplete list of open / not yet implemented features of the reader:

Compression: jpeg, CCITT Group 3, CCITT Group 4
PlanarConfiguration 2
ColorMap
separate mask
fillorder - not needed by baseline tiff reader
bigtiff 64bit offsets
XMP tag 700
ICC profile tag 34675
Orientation with rotation

Working features of the writer:

Grayscale 8,16bit (optional alpha)
RGB 8,16bit (optional alpha)
Orientation except rotated
multiple images, pages
thumbnail
Compression: deflate

Here is an incomplete list of open / not yet implemented features of the writer:

Compression: LZW, packbits, jpeg, CCIT Group 3,CCIT Group 4,...
Planar
ColorMap
separate mask
fillorder - not needed by baseline tiff reader
bigtiff 64bit offsets
endian - currently using system endianess
Orientation with rotation

Walk-through

Basic Canvas Setup

You'll need a few things to start up. A canvas, image, and writer. The writer is to write images like PNG. The sample below will give you a 100x100 black png.

{$mode objfpc}{$h+}
program demo;
 
uses classes, sysutils,
     FPImage, FPCanvas, FPImgCanv,
     FPWritePNG;
 
var canvas : TFPCustomCanvas;
    image : TFPCustomImage;
    writer : TFPCustomImageWriter;
begin
  { Create an image 100x100 pixels}
  image := TFPMemoryImage.Create (100,100);
  
  { Attach the image to the canvas }
  Canvas := TFPImageCanvas.Create (image);
  
  { Create the writer }
  Writer := TFPWriterPNG.Create;
  
  { Save to file }
  image.SaveToFile ('DrawTest.png', writer);
  
  { Clean up! }
  Canvas.Free;
  image.Free;
  writer.Free;
end.

Drawing a Circle

Drawing a circle requires a bit more then just giving a width. You'll need to setup the pen style, mode, width, and color to do this. FCL-Image comes with a few pen modes and styles, it will really be up to you to decide which you'll need. Its best for now to try with a few modes and styles to get a better understanding of what FCL-Image can do.

{$mode objfpc}{$h+}
program demo;
 
uses classes, sysutils,
     FPImage, FPCanvas, FPImgCanv,
     FPWritePNG;
 
var canvas : TFPcustomCanvas;
    image : TFPCustomImage;
    writer : TFPCustomImageWriter;
    { 
      Colors range from 0 to 65535 in each primary color. 
      They can also show as hexadecimal:
      $FFFF = 65535, $0000 = 0 
    }
    passionRed: TFPColor = (Red: 65535; Green: 0; Blue: 0; Alpha: 65535);
begin
  image := TFPMemoryImage.Create (100,100);
  Canvas := TFPImageCanvas.Create (image);
  Writer := TFPWriterPNG.Create;

  { Set the pen styles }
  with canvas do
  begin
    pen.mode    := pmCopy;
    pen.style   := psSolid;
    pen.width   := 1;
    pen.FPColor := passionRed;
  end;

  { Draw a circle }
  canvas.Ellipse (10,10, 90,90);
  
  { Save to file }
  image.SaveToFile ('DrawTest.png', writer);
  
  { Clean up! }
  Canvas.Free;
  image.Free;
  writer.Free;
end.

Drawing Alpha-Blended Shapes

Alpha-blending means: When something is painted over an existing image the old pixels are allowed to shine through the new drawing. The amount of mixing is given by the Alpha value of the new color which is specified as fourth word parameter of the brush's FPColor. Alpha=0 means: the new painting is fully transparent, Alpha=$FFFF means: the new drawing is fully opaque.

In order to activate alpha-blending the DrawingMode of the canvas must be switched to dmAlphaBlend, and the brush color of a new shape must be extended by its Alpha value.

program alphablend;
uses
  FPImage, FPImgCanv, FPCanvas, FPWritePNG;
var
  img: TFPMemoryImage;
  canvas: TFPImageCanvas;
begin
  img := TFPMemoryImage.Create(200, 200);
  canvas := TFPImageCanvas.Create(img);
  try
    canvas.DrawingMode := dmAlphaBlend;  // This activates the alpha-blend mode

    // Background
    canvas.Pen.Style := psClear;
    canvas.Brush.FPColor := colWhite;
    canvas.FillRect(0, 0, img.Width, img.Height);

    // Yellow opaque rectangle
    canvas.Brush.FPColor := FPColor($FFFF, $FFFF, 0);
    canvas.Rectangle(10, 10, 190, 100);

    // Overlapping semi-transparent red circle
    canvas.Brush.FPColor := FPColor($FFFF, 0, 0, $4000);
    canvas.Ellipse(60, 60, 140, 140);

    // Overlapping semi-transparent blue circle
    canvas.Brush.FPColor := FPColor(0, 0, $FFFF, $8000);
    canvas.Ellipse(0, 100, 100, 200);

    // Save to image file
    img.SaveToFile('alphablend.png');
  finally
    canvas.Free;
    img.Free;
  end;
end.

Pen Modes

The pen mode is how the pixel drawn will react to the pixels beneath it. So if its a white pixel and you draw a red pixel over it with the mode of pmXor then you'll get a vibrate blue pixel.

pmBlack
pmWhite
pmNop
pmNot
pmCopy
pmNotCopy
pmMergePenNot
pmMaskPenNot
pmMergeNotPen
pmMaskNotPen
pmMerge
pmNotMerge
pmMask
pmNotMask
pmXor
pmNotXor

Pen Styles

psSolid
psDash
psDot
psDashDot
psDashDotDot
psinsideFrame
psPattern
psClear

Drawing modes

dmOpaque -- painting over an existing image overwrites the pixels previously written.
dmAlphaBlend -- painting over an existing image blends the old and new colors in the ratio of their Alpha value.
dmCustom -- similar to dmAlphaBlend, but a function must be provided which defines how old and new colors are combined (TFPCanvasCombineColors = function(const color1, color2: TFPColor): TFPColor of object;).

Drawing text

Here is an example, how to create a 200x100 image, painting a white background and some text and saving it as .png:

program fontdraw;

{$mode objfpc}{$H+}

uses
  Classes, SysUtils, FPimage, FPImgCanv, ftfont, FPWritePNG, FPCanvas;

procedure TestFPImgFont;
var
  Img: TFPMemoryImage;
  Writer: TFPWriterPNG;
  ms: TMemoryStream;
  ImgCanvas: TFPImageCanvas;
  fs: TFileStream;
  AFont: TFreeTypeFont;
begin
  Img:=nil;
  ImgCanvas:=nil;
  Writer:=nil;
  ms:=nil;
  fs:=nil;
  AFont:=nil;
  try
    // initialize free type font manager
    ftfont.InitEngine;
    FontMgr.SearchPath:='/usr/share/fonts/truetype/ttf-dejavu/';
    AFont:=TFreeTypeFont.Create;

    // create an image of width 200, height 100
    Img:=TFPMemoryImage.Create(200,100);
    Img.UsePalette:=false;
    // create the canvas with the drawing operations
    ImgCanvas:=TFPImageCanvas.create(Img);

    // paint white background
    ImgCanvas.Brush.FPColor:=colWhite;
    ImgCanvas.Brush.Style:=bsSolid;
    ImgCanvas.Rectangle(0,0,Img.Width,Img.Height);

    // paint text
    ImgCanvas.Font:=AFont;
    ImgCanvas.Font.Name:='DejaVuSans';
    ImgCanvas.Font.Size:=20;
    ImgCanvas.TextOut(10,30,'Test');

    // write image as png to memory stream
    Writer:=TFPWriterPNG.create;
    ms:=TMemoryStream.Create;
    writer.ImageWrite(ms,Img);
    // write memory stream to file
    ms.Position:=0;
    fs:=TFileStream.Create('testfont.png',fmCreate);
    fs.CopyFrom(ms,ms.Size);
  finally
    AFont.Free;
    ms.Free;
    Writer.Free;
    ImgCanvas.Free;
    Img.Free;
    fs.Free;
  end;
end;

begin
  TestFPImgFont;
end.

Reading an image file

It is very easy to read image files with fcl-image, as the example below shows:

uses
  fpreadgif, fpimage;

var
  image: TFPCustomImage;
  reader: TFPCustomImageReader;
begin
  Image := TFPMemoryImage.Create(10, 10);
  Reader := TFPReaderGIF.Create;
  Image.LoadFromFile(AFileName, Reader);
  // ...

Converting between two raster image formats

To convert simply open in one format and save in the desired one, like in this example:

uses
  fpreadgif, fpimage, fpwritebmp;

var
  image: TFPCustomImage;
  reader: TFPCustomImageReader;
  writer: TFPCustomImageWriter;
begin
  Image := TFPMemoryImage.Create(10, 10);
  Reader := TFPReaderGIF.Create;
  Writer := TFPWriterBMP.Create;

  Image.LoadFromFile(AFileName, Reader);
  Image.SaveToFile(ADestFileName, Writer);
  //...

Writing an 8-bit paletted bitmap file

The following section is based on forum discussion https://forum.lazarus.freepascal.org/index.php/topic,63215.msg478472.html#msg478472.

For creating a bmp file with a color palette set the UsePalette property of the TFPCustomImage to true. Add the FPColors of the palette entries to the image's Palette property. For painting on a canvas define colors by the FPColor values in the same way as with an unpaletted image; the palette index of the requested color is determined internally. When a color is not found in the existing palette, the color is added automatically. If this is not wanted you can also specify the colors by means of the palette index: canvas.Brush.FPColor := image.Palette[1]

program PaletteBMP;

{$mode objfpc}{$H+}

uses
  classes, fpcanvas, fpimage, fpimgcanv, fpwritebmp;

var
  img: TFPMemoryImage;
  cnv: TFPImageCanvas;
  writer: TFPCustomimageWriter;
begin
  img := TFPMemoryImage.Create(100, 100);
  try
    img.UsePalette := true;
    // colBlack is always available at index 0.
    img.Palette.Add(colYellow);  // Index 1
    img.Palette.Add(colBlue);    // Index 2
    img.Palette.Add(colGreen);   // Index 3

    cnv := TFPImageCanvas.Create(img);
    try
      cnv.Brush.FPColor := colYellow;
      cnv.Rectangle(10, 10, 45, 45);

      cnv.Brush.FPColor := colBlue;
      cnv.Rectangle(55, 10, 90, 45);

      cnv.Brush.FPColor := img.Palette[3];
      cnv.Rectangle(10, 55, 45, 90);

      cnv.Brush.FPColor := colWhite;  // not yet in palette
      cnv.Rectangle(55, 55, 90, 90);
    finally
      cnv.Free;
    end;

    writer := TFPWriterBMP.Create;
    TFPWriterBMP(writer).BitsPerPixel := 8;
    try
      img.SaveToFile('test-8bpp.bmp', writer);
    finally
      writer.Free;
    end;
  finally
    img.Free;
  end;
end.

Gamma correction

FCL-Image can be used for image transformations, such as gamma correction (adjustment of pixel values to modify brightness, see https://en.wikipedia.org/wiki/Gamma_correction):

uses
  fpimage, fpreadjpeg, fpwritejpeg, math;

procedure GammaCorrection(const ASrcFile, ADestFile: String; AGamma: Double);
var
  img: TFPMemoryImage;
  reader: TFPCustomImageReader;
  writer: TFPCustomImageWriter;
  i, j: Integer;
  clr: TFPColor;
begin
  Assert(AGamma <> 0.0);

  img := TFPMemoryImage.Create(0, 0);
  try
    reader := TFPReaderJpeg.Create;
    try
      img.LoadFromFile(ASrcFile, reader);
    finally
      reader.Free;
    end;

    for j := 0 to img.Height - 1 do
      for i := 0 to img.Width - 1 do
      begin
        clr := img.Colors[i, j];
        clr.Red := round(((clr.Red / 65535)**AGamma)*65535);
        clr.Green := round(((clr.Green / 65535)**AGamma)*65535);
        clr.Blue := round(((clr.Blue / 65535)**AGamma)*65535);
        img.Colors[i, j] := clr;
      end;

    writer := TFPWriterJpeg.Create;
    try
      img.SaveToFile(ADestFile, writer);
    finally
      writer.Free;
    end;
  finally
    img.Free;
  end;
end;