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TJPEGImage component version 1.3 Luciano Bajo Eloy - Sep 9, 1997 Madrid, Spain E-mail: lbe20@tid.es Andreas Hoerstemeier - May 17, 1998 Aachen, Germany E-Mail: andy@hoerstemeier.de WWW: http://www.westend.de/~hoerstemeier ------------------------------------------------------------------------------- Note on Version 1.3: This version now adds the ability to save the JPEG as well as a TDBJPEGImage. For details see the New Features section. ------------------------------------------------------------------------------- Important note: I (Luciano) have changed my job. I do not work with Delphi currently, I use Visual C++ (I hate it, but such is life). That means that I cannot reply several mails a day pertaining to TJPEGImage. Instead I have included the source code. If you have any problems, you will have to modify the code by yourself. Please, do not send me E-mails unless it is truly necessary. Note on installation: Select the file JpgImgR.pas when installing the component ------------------------------------------------------------------------------- Index: 0. Answers to common questions and requests 1. New features (from version 1.0 to 1.1 and 1.2) 2. Introduction 3. JPEGImage properties and events 3a. DBJPEGImage additional properties and events 4. Remarkable features 5. Known limitations (future improvements?) 6. Distribution and source code 7. Information and libraries on JPEG compression ------------------------------------------------------------------------------- 0. Answers to common questions and requests ------------------------------------------------------------------------------- Basically, all of the E-mails I have received pertaining to TJPEGImage fall into one of these topics: -Requests for source code. Well, I did not provide the source code with TJPEGImage 1.0 (I sended it on request) as a mean to know if the component was being used. The result is that many people have requested it and I have had to send several mails a day with the code attached. To avoid this, I provide the full source code with this version. -Support for Delphi 3.0. Delphi 3.0 adds support for JPEG files so TJPEGImage is no longer required. Drop a TImage on a form (Image1, for example), add jpeg.pas to the uses clause and load a JPEG file with Image1.Picture.LoadFromFile. However this component also runs with D3 since V1.2, only a bit slower than the Delphi one. -Loading pictures from a stream. TJPEGImage does not support loading pictures from a stream. If you need that feature you will have to modify the code, I think it will not be difficult. (Obsolete, added with V1.2) -Coding JPEG images. TJPEGImage is a decoder, not a coder. That means that you can view JPEG files, but you cannot save files as JPEG. (Obsolete, added with V1.3). ------------------------------------------------------------------------------- 1. New features (from version 1.0 to 1.1 and 1.2) ------------------------------------------------------------------------------- From Version 1.0 to 1.1 -Finally, FileName has its own property editor by courtesy of Keith Anderson, who sent me the code by E-mail. -A new property and a new event have been added for indicating the progress of the decompression (see section 2 for details). -A bug has been fixed. When a corrupted JPEG file was loaded into the component the file was being left open. Any further action on this file generated a Sharing Violation exception (IOResult = 32). The bug has been reported and fixed by Derek (sorry, I do not know your last name). From Version 1.1 to 1.2 (changes done by Andreas Hoerstemeier) -The component can now also load the image from any stream, it now has a LoadFromStream method, so it can also be used to display files out of a database (TBlobStream) or downloaded from the web without the need of a temporary file. -As the whole PasJPG library didn't include any 32bit specific parts the component could be modified easily for Delphi 1 (but note it is slow there compared to Delphi 2), and in the same way to work with Delphi 3, too. It may also run in C++ Builder, but I've no chance of testing this. From version 1.2 to 1.3 (changes done by Andreas Hoerstemeier) -The coding part of the JPEG library is now also included and connected to the component. -A new TDBJPEGImage is included which allows to you to link a BLOB field containing JPEG images to a visual control easily. From version 1.3 to 1.4 (changes done by Andreas Hoerstemeier) -New property Comment to link to the optional comment within the JPEG file. ------------------------------------------------------------------------------- 2. Introduction ------------------------------------------------------------------------------- JPEGImage is based on the work of NOMSSI NZALI Jacques H. C., author of the PASJPEG library (http://www.tu-chemnitz.de/~nomssi/pub/pasjpeg.zip). On his own words, PASJPEG is a port of the sixth public release of the IJG (Independent JPEG Group) C source (release 6a of 7-Feb-96), that implements JPEG baseline, extended-sequential, and progressive compression processes to Turbo Pascal 7.0 for DOS (TP). My goal was to get a Delphi component for decompressing and viewing JPEG images. So I began from DJPEG.PAS, a DOS program written by Thomas G. Lane included in the PASJPEG library for translating JPEG files to BMP or TARGA files. My work has consisted of the following steps: 1. Create a new component inherited from TImage. 2. Change command line options in DJPEG to properties in TJPEGImage. 3. Fit the output in a memory stream instead of a disk file. 4. Change WriteLn and Halt procedures to Delphi exceptions. 5. Put the library on a diet, that is, delete unnecessary files and code. Once those steps where covered, I found a problem in 256 colors video mode: the first image loaded had the right colors, but successive images caused the color palette to become corrupted. Fortunately, I was a little luck and I could solve the problem. ------------------------------------------------------------------------------- 3. JPEGImage properties and events ------------------------------------------------------------------------------- The properties of TJPEGImage are (apart from those in TImage): -FileName: Name of the JPEG file. -NumOfColors: Colors of the resulting image. Possible values are _16, _256, or TrueColor. DO NOT use TrueColor in 256 video modes or the colors in the image will become distorted. (Default 256). Not used for saving as JPEG images can only be true color or grayscale. -DCTMethod: Method used for the Discrete Cosine Transform in JPEG algorithms. Possible values are Integ (default), FastInteg (faster but less accurate) or FloatingPoint (more accurate but slower). -Dither: Possible values are none (do not use dithering in quantization), FS (default) or ordered (medium speed, quality). Not for saving. -GrayScale: Force grayscale output (default False). -NoSmooth: Do not use high-quality upsampling (default False). Loading only.