Delphi Image Resizing - Felix John COLIBRI.

• abstract : resizing JPG images using the Graphics32 library. Load the JPEG, possibly rotate it, scale it, save it as a .PNG
  
• key words : .JPG, .JPEG, .PNG, image resizing, image rotation, .JPEG to .PNG conversion, Graphics32, tKernelResampler, tImage32, tBitmap32
  
• hardware used : intel i3-8100, 3.6 gHz, 8GB memory, 128 G and 1 T hard disc
  
• software used : Windows 10 64 bit, Delphi 7
  
• scope : Delphi 1 to 7, 2006 to 2010, Xe, Seattle, Tokyo, Berlin, 10.3
  
• level : Delphi developer
  
• plan :
  
  • Resizing Jpeg Images
    
  • Delphi Image Resizing App
    
  • Comments and links
    
  • Download the Sources
    

1 - Resizing Jpeg Images

Using Delphi tBitMap.StretchDraw is quite easy, but the result is poor. So, looking at StackOverflow, the best solutions presented was to use Graphics32 library.

This article simply presents an application which uses this library to resize images

2 - Delphi Image Resizing App

2.1 - Graphics32 image library

2.2 - The Delphi Application

The overall project structure is the usual tDirectoryListBox / tFileListBox combination.

Clicking on a .JPG file in the tFileListBox

• loads the .JPG in a tImage32 object and computes the destination width and height which matches a 500 pixel width best

  Procedure _load_image_32;   Begin     g_c_image_32.Free;     g_c_image_32:= TImage32.Create(Nil);     With Form1 Do     Begin       g_c_image_32.Bitmap.LoadFromFile(g_path+ g_file_name);       With Image1.Picture.Bitmap Do       Begin         Width:= 0;         Height:= 0;       End; // with Image1.Picture.Bitmap       Image1.Picture.Bitmap.Assign(g_c_image_32.Bitmap);       With Image1.Picture.Bitmap Do       Begin         g_original_width:= Width;         g_original_height:= Height;         l_ratio:= 500 / Width;         l_power:= 1;         For l_index:= 1 To 10 Do         Begin           If 1/ l_power< l_ratio             Then Begin                 g_destination_width:= Round(Width / l_power);                 g_destination_height:= Round(Height/ l_power);                 Break;               End;           l_power:= l_power* 2;         End; // for l_index       End; // with Image1.Picture.Bitmap     End; // with Form1   End; // _load_image_32

  the g_ being obvious global variables you will find in the .ZIP

• then clicking on a Button resizes the bitmap and, if save_ is Checked, saves the result in the parent directory:

  Procedure resize_image32_3;   Procedure _set_high_quality_stretch_filter(p_c_bitmap_32: TBitmap32);     Var l_c_kernel_resampler: TKernelResampler;     Begin       If Not (p_c_bitmap_32.Resampler Is TKernelResampler)         Then           Begin             l_c_kernel_resampler:= TKernelResampler.Create(p_c_bitmap_32);             l_c_kernel_resampler.Kernel:= TLanczosKernel.Create;           End         Else           Begin             l_c_kernel_resampler:= p_c_bitmap_32.Resampler As TKernelResampler;             If Not (l_c_kernel_resampler.Kernel Is TLanczosKernel)               Then                 Begin                   l_c_kernel_resampler.Kernel.Free;                   l_c_kernel_resampler.Kernel:= TLanczosKernel.Create;                 End;           End;     End; // _set_high_quality_stretch_filter   Var l_c_source_bitmap_32, l_c_destination_bitmap_32: TBitmap32;       l_file_name: String;   Begin // resize_image32_3     With Form1 Do     Begin       size_label_.Caption:= Format('%4d  %4d',           [g_destination_width, g_destination_height]);       l_c_source_bitmap_32:= tBitMap32.Create;       l_c_source_bitmap_32.Assign(Image1.Picture.Bitmap);       _set_high_quality_stretch_filter(l_c_source_bitmap_32);       l_c_destination_bitmap_32:= TBitmap32.Create;       l_c_destination_bitmap_32.SetSize(g_destination_width, g_destination_height);       l_c_source_bitmap_32.DrawTo(l_c_destination_bitmap_32,           Rect(0, 0, g_destination_width, g_destination_height),           Rect(0, 0, l_c_source_bitmap_32.Width, l_c_source_bitmap_32.Height));       FreeAndNil(l_c_source_bitmap_32);       With l_c_destination_bitmap_32 Do       Begin         If _90.Checked           Then Rotate90 Else         If _180.Checked           Then Rotate180 Else         If _270.Checked           Then Rotate270;         Image2.Picture.Bitmap.Assign(l_c_destination_bitmap_32);         If save_.Checked           Then Begin               l_file_name:= ChangeFileExt(g_file_name, '.png');               SaveBitmap32ToPNG(l_c_destination_bitmap_32, g_path+ '..\'+ l_file_name);               ClipBoard.AsText:= l_file_name;             End           Else ClipBoard.AsText:= '';         Free; // l_c_destination_bitmap_32       End; // with l_c_destination_bitmap_32     End; // with Form1   End; // resize_image32_3

  
  

2.3 - Mini HowTo

and

• create a directory for the resulting resized .PNG
  
• create a sub-directory and place all your .JPG in this directory

• start delphi_resize_images.exe
  
• in the DirectoryListBox1, select the .JPG directory
  
• for as many images as you like
  
  • select a .JPG in the FileListBox1
    
  • if the image is not upright, rotate it by clicking _90, _180 or _190
    
  • click one of the resizing button: size_ for the computed sizes, size_15_ for 1.5 size and size_2_ for double target size
    
  • if the result is satisfactory, check save_, click one of the size_ buttons, and
    • the result will be saved in the parent directory
      
    • the file name will bs stored in the ClipBoard (for inserting in the .HTML <IMG tag)
      

3 - Comments and links

3.1 - Comments

• we only computed the resizing based on a hard coded 500 pixel width. This could be placed in an Edit, and the computations could take the Width or Height, depending on the portrait or landscape display of the image
  
• the 500 pixel value is a self imposed limit: we want to avoid scrolling of the .HTML page, and for 778 width screen pages, this is a reasonable figure.
  
• I basically assumed that dividing the image size by powers of 2 would result in better compression (less artifacts), but did not check. If the Graphics 32 algorithm is not sensible to this factor, we could avoid the power of 2 computations and resize exactly to fit the target size (500 pixel width in our case)
  
• the procedures should also be parameterized instead of using globals
  
• there still remains an update problem (which we also had with our StretchDraw program): when size_ is clicked, the image is not always displayed. Selecting the display_ tabsheet and the resized_ tabs again forces a refresh and solves the problem, in a somehow unsatisfactory way
  

3.2 - Links

• The superb Graphics32 library web page
  
• Un Colibri à Prague is the pages for which this project was created. A remarkable city I very much enjoyed visiting
  

4 - Download the Sources

• zip_delphi_resize_images.zip: the resizing project (without the Graphics32 units) (44 K)
  

The .ZIP file(s) contain:

• the main program (.DPR, .DOF, .RES), the main form (.PAS, .DFM), and any other auxiliary form
  
• any .TXT for parameters, samples, test data
  
• all units (.PAS) for units
  

• are self-contained: you will not need any other product (unless expressly mentioned).
  
• for Delphi 6 projects, can be used from any folder (the pathes are RELATIVE)
  
• will not modify your PC in any way beyond the path where you placed the .ZIP (no registry changes, no path creation etc).
  

• create or select any folder of your choice
  
• unzip the downloaded file
  
• using Delphi, compile and execute
  

The Pascal code uses the Alsacian notation, which prefixes identifier by program area: K_onstant, T_ype, G_lobal, L_ocal, P_arametre, F_unction, C_lass etc. This notation is presented in the Alsacian Notation paper.

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5 - The author