{
  Vampyre Imaging Library
  by Marek Mauder
  http://imaginglib.sourceforge.net

  The contents of this file are used with permission, subject to the Mozilla
  Public License Version 1.1 (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.mozilla.org/MPL/MPL-1.1.html

  Software distributed under the License is distributed on an "AS IS" basis,
  WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for
  the specific language governing rights and limitations under the License.

  Alternatively, the contents of this file may be used under the terms of the
  GNU Lesser General Public License (the  "LGPL License"), in which case the
  provisions of the LGPL License are applicable instead of those above.
  If you wish to allow use of your version of this file only under the terms
  of the LGPL License and not to allow others to use your version of this file
  under the MPL, indicate your decision by deleting  the provisions above and
  replace  them with the notice and other provisions required by the LGPL
  License.  If you do not delete the provisions above, a recipient may use
  your version of this file under either the MPL or the LGPL License.

  For more information about the LGPL: http://www.gnu.org/copyleft/lesser.html
}

{
  This unit contains various image comparing functions and image difference
  computations.
}
unit ImagingCompare;

{$I ImagingOptions.inc}

interface

uses
  SysUtils, Classes, ImagingTypes, Imaging, ImagingFormats, ImagingUtility;

{ Computes various error metrics for two images. Images must have
  the same size and format. Only formats with 1, 2, and 4 byte samples are
  supported (no indexed, compressed, etc.).}
procedure ComputeErrorMetrics(const Image1, Image2: TImageData;
  var PSNR, MSE, RMSE, PAE, MAE: Single);

implementation

procedure ComputeErrorMetrics(const Image1, Image2: TImageData;
  var PSNR, MSE, RMSE, PAE, MAE: Single);
var
  I: Integer;
  Info: TImageFormatInfo;
  Samples, Bps: Integer;
  PixelPtr1, PixelPtr2: PByte;
  Diff, MaxSample: Single;
begin
  GetImageFormatInfo(Image1.Format, Info);
  Bps := Info.ChannelCount div Info.BytesPerPixel;
  Assert((Image1.Width = Image2.Width) and (Image1.Height = Image2.Height) and
    (Image1.Format = Image2.Format));
  Assert(not Info.IsIndexed and not Info.IsSpecial and not Info.UsePixelFormat
    and (Bps in [1, 2, 4]));

  Diff := 0;
  PSNR := 0;
  MSE  := 0;
  RMSE := 0;
  PAE  := 0;
  MAE  := 0;
  PixelPtr1 := Image1.Bits;
  PixelPtr2 := Image2.Bits;
  Samples := Image1.Width * Image1.Height * Info.ChannelCount;

  for I := 0 to Samples - 1 do
  begin
    // Compute difference betwen pixels
    case Bps of
      1: Diff := Abs(PixelPtr2^ - PixelPtr1^);
      2:
        begin
          if Info.IsFloatingPoint then
            Diff := Abs(HalfToFloat(PWord(PixelPtr2)^) - HalfToFloat(PWord(PixelPtr1)^))
          else
            Diff := Abs(PWord(PixelPtr2)^ - PWord(PixelPtr1)^);
        end;
      4:
        begin
          if Info.IsFloatingPoint then
            Diff := Abs(PSingle(PixelPtr2)^ - PSingle(PixelPtr1)^)
          else
            Diff := Abs(PUInt32(PixelPtr2)^ - PUInt32(PixelPtr1)^);
        end;
    end;

    // Update metrics
    MAE := MAE + Diff;
    PAE := MaxFloat(PAE, Diff);
    MSE := MSE + Diff * Diff;

    Inc(PixelPtr1, Bps);
    Inc(PixelPtr2, Bps);
  end;

  if Info.IsFloatingPoint then
    MaxSample := 1.0
  else
    MaxSample := Pow2Int(Bps * 8) - 1;

  // Final metrics calculations
  MAE := MAE / Samples;
  MSE := MSE / Samples;
  RMSE := Sqrt(MSE);
  if RMSE < 0.0001 then
    PSNR := 1e06
  else
    PSNR := 20 * Log10(MaxSample / RMSE);
end;

{
  File Notes:

  -- TODOS ----------------------------------------------------
    - none

  -- 0.26.5 Changes/Bug Fixes -----------------------------------
    - Added ComputeErrorMetrics.
    - Unit created.
}

end.