Bitmap Basics - A GDI tutorial

Download Tutorial 1 Source - 42Kb

Download Tutorial 2 Source - 10Kb

Download Tutorial 3 Source - 28Kb

Download Tutorial 4 Source - 29Kb

Windows GDI Tutorial 1 - Drawing a bitmap

Bitmaps and palettes are both potentially the most useful part and most confusing parts of the GDI subsystem to neophyte coders. In this, and the following GDI tutorials I will explain how to draw bitmaps onto a window, how to implement bitmap transparency and how to draw animations in a window without any flicker or flashing.

This being the first tutorial I start by explaining the basic concepts of a device context, and how to properly use them.

GDI & DC's

GDI stands for "Graphics Device Interface", DC for "Device Context". The designers of Windows decided that it would be nice to have a single way of drawing to all "things", and thus developed GDI as a universal set of routines that can be used to draw onto a screen, printer, plotter or bitmap image in memory.

The GDI library is based around an object called a Device Context. A Device Context is a handle to a drawing surface on some device - Device Contexts can typically be obtained for the display device (the entire screen), printers and plotters. Most commonly worked with are window dc's (a display DC that merely represents the area of a single window) and a memory DC that represents a bitmap as a device.

What these objects all have in common (display, printer, bitmap, etc) is they have some concept of a "drawing surface" where output will appear.

Associated with a Device context a number of tools that can be used to act on the associated drawing surface: Pens, brushes, fonts etc. In the case of physical devices like a plotter there will be a one to onw mapping of HPEN to physical pen. In the case of the display, or memory DC's, a number of preset pens are provided, and more can be created on the fly as needed.

BITMAPS

A Bitmap is the in-memory representation of a drawing surface. By "selecting" a bitmap into a memory DC, the DC then represents that bitmap as a drawing surface, and all the normal GDI operations can be performed on the bitmap. GDI also has a number of functions that can copy areas from the drawing surface of one DC to another, so bitmaps then are a useful way to store images in memory that will later be copied to the display (or other devices).

A Bitmap that can be slected into a DC is called a "Device Dependent Bitmap" and is represented to the programmer by an HBITMAP handle.

There is another kind of Bitmap called a "Device Independent Bitmap". This type of bitmap is defined in the windows header files as a number of structs that are filled in by the programmer. Being "device independent" means there is no HBITMAP that can be selected into a "Device context" so GDI operations cannot be performed on this type of bitmap. There are a couple of "DIB" specific functions that can create a DDB (device dependent bitmap) given a DIB, or copy areas from a DIB onto a DC.

The Tutorial

In this tutorial (GDI01) I demonstrate how to load a bitmap resource as a device dependent bitmap, and how to display the bitmap on a window. The bitmap is loaded in the applications WM_CREATE handler, and shown in the applications WM_PAINT handler.

In GDI tutorial 2 I will demonstrate how to implement bitmap transparency using Device Dependent Bitmaps.

The tutorial comprises a single window that I create in main.cpp. Stored in a global variable is the bitmap handle that is initialized in the OnCreate() function, used in OnPaint(), and destroyed in OnDestroy(). The example bitmap shipped with the tutorial is a 256 color image, and will appear rather flat on a 256 color display. The lack or proper color on 256 color displays will be fixed in tutorial 3 where I intend to discuss palettes.

Windows GDI Tutorial 2 - Transparency

Simple bitmap graphics is quite powerfull. Soon however one gets to a situation where one wants to overlap two non-rectangular images. Windows bitmaps are "unfortunately" rectangles so what one needs to do is mark certain areas of the bitmap as "not part of the image". In other words: transparent.

GDI has no built in transparency support - you have to implement transparency in bitmaps yourself. Specific versions of GDI have had support for transparent areas in a bitmap - NT4 for instance has a specif function, and the VFW kit for Windows 3.11 included an extended devmode option that could be set in a DC to specify that the color set in SetBkColor was to be transparent. These methods however are not compatible with other platforms (notably Windows 95) and should probably be avoided.

A Simple Method

The most simple method to implement a bitmap with "transparent" areas is to have two bitmsps. One bitmap specifies the image - and all the "transparent" areas are set to black. The other bitmap is monochrome / black and white. This bitmap has white pixels around the edges of the image. The black pixels forming a siloette of the image.

GDI supports boolean operations when combinig the contents of DCs surfaces, and we use this to our advantage here. To paint a "transparent" bitmap pair onto a DC the following process is performed:

1. Blit the monochrome bitmap onto the destination using SRCAND as the raster code. The SRCAND code directs GDI to set each destination pixel as the binary and of the destination pixel and the source pixel. In this case black acts like zero, and white like all 1's: Destination pixels where the source are black become black. Destination pixels where the source is white are left untouched. The effect is of a hole being cut in the destination image.

2. Blit the color image bitmap onto the destination using SRCPAINT. The SRCPAINT raster code directs GDI to set each destination pixel as the binary OR of the previous destination value and source pixel. Now, due to the previous step, wherever the source has non-black pixels the destination has been zero'd. And zero OR something is that something. So, this step combines the two images seamlessly.

A Different method

The above method of having paired bitmaps, a color image bitmap, and a monochrome mask is in terms of GDI operations the simplest. Some people however perfer not to supply a 2nd monochrome mask image: They specify the transparent areas of the bitmap by assigning a certain color to be transparent. This color fills the area around the image, and care must be taken not to use the "magic" color in the image itself.

Also, special care must be taken when using this kind of bitmap with GDI on low color displays: GDI always creates "compatible" DDBs (and you the programmer always wants to use "compatible" bitmaps) in the format of the display mode. This can result in a loss of color "resolution" and a whole range of colors might be mapped to the magic transparent color. It is therefore best to make sure that the transparent color is one of the twenty system colors that are guaranteed to always exist.

Monochrome Bitmaps

Dealing with monochrome bitmaps can at first be tricky due to the lack of explicit documentation dealong with how they interact with color bitmaps. In the example code I Blit directly from a color bitmap to a monochrome bitmap, and later in the reverse direction. To figure out whats going to happen in this situation you have to know how GDI maps monochrome bitmap pixels to color bitmap pixels.

The background "color" of a bitmap is white, and is stored as binary 0. When combined with a color bitmap via a raster operation (typically in a call to BitBlt) the background pixels in the monochrome bitmap are first mapped to the background color of the color bitmaps DC. This is normally set to white (RGB(255,255,255)), but can easilly be changed by using the SetBKColor() API. The foreground pixels of a monochrome bitmap (binary 1) is mapped to the text color of destination DC - default is black (RGB(0,0,0)), but once again the SetTextColor() API can be used to change that.

When transferring bytes from a color to a monochrome bitmap, the mapping is simpler. All pixels that are the same color as the background color are mapped to the background color on the mono bitmap (0). All other pixels are demed to be foreground.

Raster Operations

Raster operations (SRCPAINT, SRCCOPY) etc are performed only after any mapping has taken place. They are performed bytewise on the image bytes. this is the most efficient means of operation, but it means that logical raster operations performed on 256 color displays will tend to have unexpected results, as any palettes are totally ignored by this process. The default twenty system colors will behave in an expected way, as the system palette has been arranged specially so the mappings work. Instead of simply using the 1st twenty colors, the system palette uses the first ten, and last ten colors, so when a NOT is performed on black (color index 0) the result of the NOT operation (color index 255) is the expected white.

The Tutorial

The code demonstrates how to create a monochrome bitmap from the color image. The code uses a simple method to find out what color to use as the transparent color - it checks the color of the top left pixel. The files, when compiled and run should procude a window with an irritating checkerboard pattern. The transparent image is painted over this checker pattern. The files to download are listed at the top of this article.

The relevent functions in main.cpp are heavily commented. Look in the WM_CREATE handler where the main bitmap is loaded and a monochrome version is generated. The WM_PAINT handler demonstrates how to blit the two bitmaps correctly. WM_DESTROY cleans up the two bitmaps. Also look in the RegisterClass() function of the frame to see where the checkered background is set.

Whats to come

In the next gdi tutorial I look at:

• loading bitmap resources manually.
• Creating bitmaps and palettes from bitmap resources.
• Using palettes correctly to ensure color fastness on 256 color display hardware.

In tutorial 4 I will examine some advanced uses of DIBs. While slower than the DDBs weve been using up till now they are ameanable to a number of tricks that make them quite useful.

Windows GDI Tutorial 3 - Using Palettes and accessing bitmap resources

Trying to figure out how to implement palette support can be a quite messy process. The documentation that exists is never entirely clear on what approach one should be taking and what to do when it doesn't work. So...

Loading resources directly

Bitmap resources, and bitmap files on disk, are stored in the windows DIB format. As a resource, a bitmap consists of a BITMAPINFO structure describing the bitmap followed by the actual image data as an array of bytes. On disk in a .bmp file, the file starts with a BITMAPFILEHEADER structure, followed by a BITMAPINFO structure. The start of the image data is indicated by a field in the BITMAPFILEHEADER structure, and does not necessairly follow the BITMAPINFO structure directly. This diffrence introduces some annoying incompatiblities when dealing with bitmap resources, and bitmap files.

The LoadBitmap() function, while simple to use, is too braindead to be used in a situation where your application requires palette support, as it creates all bitmaps using the system default palette which only has 20 colors. While only a problem on 256 color display setups, its a very ugly problem - all your loaded bitmaps are displayed with a mere 20 colors.

The solution is to use the resource functions to load the bitmaps directly using the resource functions to search the exe file for the bitmap resource, and get pointers to the resource data. As we know the data is stored in DIB format, we can use the CreateDIBitmap() API to create a DDB from the DIB data.

Palettes and Bitmaps

A bitmap to windows is just an array of bytes. In 16 bit and higher modes the color information of the bitmap data is encoded directly in the data. In 256 color mode however there is no color information stored in the bitmap. Each byte in the bitmap is simply an index into a palette of colors.

So, any operations performed on a bitmap will be performed by GDI will be done using the current selected logical palette.

Please note that the phrase "logical palette" refers to a GDI palette object - refrenced by a HPALETTE handle. The physical palette refers to the state of the actual display device palette.

Now, the quickest way to blit a bitmap onto the display would be a simple memcpy operation. And GDI does this as much as possible. In order for the results to look pleasing however, the bytes of the bitmap have to match the correct entries in the physical palette. To ensure this GDI, when it first realizes a palette, creates a mapping of logical palette entries to the system palette at the time. GDI expects that the next time the palette is realized it will be able to take the same mapping.

The bytes in a bitmap then are drawn from this cache table - NOT the logical palette.

Anyway. The whole subject is very hairy, and all I can suggest is a full reading of all the available dox you can find on palettes if you wish to truly understand the subject.

The following notes may ease some potential confusion:

• Realization is a once off thing. Once RealizePalette() has been called on an HDC, that HPALETTE does not need to be realized again until UnRealizePalette() is called, or WM_PALETTECHANGED or WM_QUERYNEWPALETTE indicates the Palette Manager itself has unrealized all palettes and is starting again. You can select and deselect a HPALETTE as many times as you wish without having to call RealizePalette().
• The last parameter to RealizePalette() can always be set to FALSE. TRUE would only be used if you were realizing a window DC and specifically do not want the palette to get mapped into the physical palette.
• Always make sure the palette that a bitmap was created with is selected into any DC you select the bitmap into (the order does not matter).
• BitBlt between memory DCs requires that the target DC has the same palette selected as the source DC.
• BitBlt from memory DC to Screen DC requires the source palette is realized.

Windows GDI Tutorial 4 - DIBs

Welcome to GDI tutorial 4 - In this tutorial I am going to concentrate on Device Independent Bitmaps.

DIBs and Bitmap resources

As should hopefully be clear by now, a bitmap resource is stored as a device independent bitmap. The resource data contains the BITMAPINFO struct, followed by an array of bytes. Passing pointers to these two structs allows loaded bitmap resources to be used directly with all windows API functions that work with DIBs.

A restriction that should be noted: As resources are paged out of the exe or dll file they were loaded from, care should be taken to avoid writing to the memory. Under Win16, all changes written to a resource might be lost if the resource is unlocked and relocked. Under Win32, writing to resource memory causes a memory exception that the operating system handles to create a duplicate resource.

DIBs and bitmap files

Bitmap files too can be directly used as a DIB once loaded into memory. The one diffrence between files and resources is that the file starts with a BITMAPFILEHEADER struct. This struct is directly followed by the BITMAPINFO struct containing the information about the DIB and the color table if present. The BITMAPFILEHEADER struct also unfortunatly contains a file offset to the DIBs byte array, so in a bitmap file the byte array might not follow directly after the BITMAPINFO structure.

Some resource compilers do not handle bitmap files properly if the bitmap data does not follow directly from the BITMAPINFO struct. They write the padded out information into the resource - in that case there is now way for the bitmap loading code to know that there is a gap between the header and bits, and the image appears corrupted.

Other Image formats and DDBs

The most efficient way to work with images is to use device dependent bitmaps. GDI stores DDB bitmaps in the format of the display device - thus DDBs are the most efficient way to work with images. GDI however does not let the programmer touch the bits of a DDB directly. GDI does however have a number of functions that allows the programmer to transfer date from DIBs to DDBs and the reverse direction. These transfer operations are slow, as GDI has to translate each pixel on the soure DDB or DIB to its nearest representation on the target DIB or DDB.

When loading or saving image formats other that bitmaps from DDBs the programmer therefore usually finds theirself working with the data as a DIB.

GDI provides the following functions to transfer bits from DIBs to DDBs, DDBs to DIBs and DIBs to DCs:

• CreateDIBitmap() - this function creates a compatible device dependent bitmap, and initializes it with the passed in DIB.
• GetDIBits() - this functions translates a DDBs data into a DIB that is passed in.
• SetDIBits() - Like CreateDIBitmap(), this function intializes a DDB using the DIB data that is passed in.
• SetDIBitsToDevice() - This function copies a DIB directly (translating each pixel of course) onto a display device context.
• StretchDIBits() - This function is similar to StretchBlt(), it stretches the source onto a DCs surface - the source data is a DIB.

DIBs and palettes and converting

When translating data from a DIB onto a DDB in a SetDIBits(), SetDIBitsToDevice(), or StretchDIBits() call, GDI has a lot of work to do. Even more so if the target display device is operating in 256 (or any other palette) mode.

The logic that GDI uses to convert a pixel is thus: First, GDI resolves the RGB value of the source (DIB) pixel it is converting. If the DIB is itself has a color table, the pixel index is looked up in the color table, and the retrieved RGB color is used in the GDI operation. Now, RGB value in hand, GDI looks up the RGB value and matches it to the closest color found in the device contexts palette. (all the above calls take a device context - The DC is in a couple of cases merely a carrier of an hpalette). The color in the logical palette is then matched to a color in the physical palette, any raster operations (in the case of SetDIBitsToDevice() or StretchDIBits()) are now applied using the physical index, and the result is stored (on the display or target DDB).

On non palette devices the situation is much simpler. After the RGB value of the DIB pixel is found, it is combined with the target RGB using the given raster operation.

DIB Transparency

A common method of implementing transparency with DDBs is to have a color bitmap, and an associated monochrome bitmap containing a mask. The mask bitmap is combined with the target DC using the SRCAND raster operation. All white pixels leave the destination untouched, all black pixels zero the destination - effectivly cutting a black hole in the target. The color bitmap is then combined with the destination using the SRCPAINT raster operation. This operation ORs each color pixel from the color image with a blacked out pixel in the destination. The source image itself is black where the destination has been left, leaving the non-transparent pixels untouched - the transparent pixles now contain the image.

A similar method is used with DIBs, but the DIB method does not require two complete DIB's *IF* the DIB has a color table. By blitting the same DIB data twice, once SRCAND with a color table intialized with each tranparent color index set to white, and "data" indexes set to black, and once SRCPAINT with the color table set up with data indexes contianing the correct color, and transparent indexes containig black, the same effect is achieved.

Note: On 256 color displays the DIB method will fail if the logical palette selected into the destination dc does not contain entries for black and white. This is due to the fact (mentioned above) that the DIB pixels are first matched to the closest entriy in the logical palette, and the found entry from the logical palette is then mapped to the physical palette (that always has the 20 system colors including black and white) before the raster operation is performed.

The Tutorial

By now you should recognise the simple tutorial. Once again you will see the aeroplane over a background of clouds. This time the aeroplane and clouds are displayed using DIBs. The demo_OnPaint() function has all the fun stuff as usual. In addition to the bmpapi files there is a primitive DIB holder class in dib.cpp and dib.h. The files you will need are at the top of this article.

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No Tranparent bitmap videoDev 1:11 27 Aug '09   Hi thanks for this nice article.I have succeeded to compile this Tutorial 2 application & run it. But to no avail i am able to see a tranparent bitmap.All i can see is full window is filled with airPlane images.No CheckerBoard pattern is shown. I want to apply tranparency to the text drawn into the Bitmap.My Bitmap is created with GDI+ method & text is drawn using GDI(DrawText for Performance).I get Color object from GDI+ to be applied to Text.GDI only takes RGB values from Color object of GDI+ , No Alpha. Any help or direction is greatly appreciated. Sign In·View Thread·PermaLink how can i create four picture from one,,,,? Mortezai 2:59 15 Jul '09   please tel me how i can make four image with x,y resolution , from the input pic of x*2,y*2 image resolution , so that the first of output except of using the average colour of four square pixels for the first pixel use the first left pixel of four square pixel and the second picture use the right top pixel , third use the bottom right, and the fourth use the left bottom , i use the setpixel and getpixel method for it, but it is too slow , i think if i use method of changing th image to array it will be very faster, please tel me ho i use the array method. this is my code in vb.net but too slow : For y = 0 To picy.Height - 1 Step 2 j = Int(y / 2) For x = 0 To picy.Width - 1 Step 2 i = Int(x / 2) pic(0).SetPixel(i, j, picy.GetPixel(x, y)) pic(1).SetPixel(i, j, picy.GetPixel(x + 1, y)) pic(2).SetPixel(i, j, picy.GetPixel(x + 1, y + 1)) pic(3).SetPixel(i, j, picy.GetPixel(x, y + 1)) Next x Next y Sign In·View Thread·PermaLink Create DIBitmap - Blackbackground Member 3812396 22:55 4 Nov '08   Hi, I am currently using the following routine to export an image which has transparent background from an Metafile. I am using the following routine. But the exported images has black background. Also please note that these images are transparent bitmap and pngs. Is there any way to avoid blackbackground, my intention is to have transparent background. private Bitmap GetBitmap( int imageOffset, uint imgSize, IntPtr ptr, IntPtr bitmapInfoPtr, int iUsageSrc ) { imageOffset -= ( 2 * IntSize ); IntPtr imgPtr = new IntPtr( ptr.ToInt64() + imageOffset ); byte[] imgData = new byte[ imgSize ]; Marshal.Copy( imgPtr, imgData, 0, imgData.Length ); IntPtr hBitmap = GdiApi.CreateDIBitmap(Objects.Handle, bitmapInfoPtr, WinGdiConst.CBM_INIT, imgData, bitmapInfoPtr, (uint)iUsageSrc); Bitmap bmp = null; if( hBitmap != IntPtr.Zero ) { // Clone image for preventing disposing it before document save. bmp = Image.FromHbitmap( hBitmap ); bmp = bmp.Clone() as Bitmap; } else { Debug.WriteLine( "Can't create bitmap" ); } GdiApi.DeleteObject( hBitmap ); return bmp; } Thanks in advance, Karthik Sign In·View Thread·PermaLink how to load BITMAP into the picture control of dailog box? smart_me 1:56 28 May '08   waiting to listen you guys. any quick help as i am new to this field (just 1 week). Rex Sign In·View Thread·PermaLink 1.00/5 (1 vote) Re: how to load BITMAP into the picture control of dailog box? qiny214 3:15 18 Jun '08   google has some samples about this. Sign In·View Thread·PermaLink 1.00/5 (1 vote) VIMP: How to convert Color BITMAP into the monochrome BITMAP in windows programming?? smart_me 1:55 28 May '08   Hi guys, does any one know how to display the monochrome image from colored BITMAP? Thanks Rex Sign In·View Thread·PermaLink 1.67/5 (3 votes) How to caputre a image? huangdejian 1:23 22 May '08   i am a neophyte ,some body can suggest me how can it possible or if possible then give me sourcecode/link that will be helpful to me? my email http://dejian_huang@163.com Sign In·View Thread·PermaLink 1.00/5 (2 votes) Windows GDI vb.net web app honkie_thong 19:22 4 Nov '06   Hi guys, I need some help regarding windows GDI. I need your help on some errors. 1. webform1.aspx has one button 2. user press the button 3. the pic with the gdi lines will be shown(Ive create a memorystream to store the image) 4. the webform1.aspx button will b gone Anyway where i can retain the button at webform1.aspx? Is it anyway where i can allocate a space in the webpage to display the form? OR can i use javascript to open a window where i can show the image with the GDI lines? Tks for helping =) Sign In·View Thread·PermaLink 2.00/5 (1 vote) Comparing 2 Images KK Gian 0:43 30 Oct '06   Greetings, How can I comparing 2 images and tell the percentage of similirity? These 2 images may not take at the same position and time, but it's the same object. Regards Gian Sign In·View Thread·PermaLink 1.00/5 (1 vote) Loading Monochrome Bitmaps in CDialog. venkateshcs 18:30 16 Oct '06   I need to load a monochrome bitmap in to a picture control in Dialog. Using Bitblt function the white color in bitmap is changed to backgroud color of the dialog. I am not able to display the white color. How to solve this problem venkatesh cs Sign In·View Thread·PermaLink 1.86/5 (6 votes) Re: Loading Monochrome Bitmaps in CDialog. smart_me 1:50 28 May '08   Dude, how did u load the monochrome bitmap in to a picture control using Bitblt winapi? chill Sign In·View Thread·PermaLink HBITMAP HELP Manni Singh 10:22 25 Jul '06   Hey i want to Load Bitmap Images from outside from my disk , not from Resource. i tried lots of ways to load images from my Disk Drive. like: LoadBitmaps(CDC *pDC) { .... ...... CDCBuffer mFace; HBITMAP hBmp; hBmp = (HBITMAP) ::LoadImage(AfxGetInstanceHandle(),pPathtoImage,IMAGE_BITMAP,0,0, LR_LOADFROMFILE); mFace.AttachBitmap(hBmp , pDC); ......... ... } but when i load this type , it s does not show anything on the Dialog plzz help me. ! Sign In·View Thread·PermaLink Re: HBITMAP HELP Christian Graus 12:04 25 Jul '06   Your loadimage command is fine. What is CDCBuffer ? Christian Graus - Microsoft MVP - C++ Metal Musings - Rex and my new metal blog Sign In·View Thread·PermaLink 2.00/5 (1 vote) Upside down bitmap alveru_78 5:30 3 Apr '06   I have a problem with bitmaps. I use my own routines to open a Bitmap file. Everything seems ok when I open and display a bitmap sometimes, but there are some bitmaps that, when I open them, they appear upside down when I display them. If a modify the code to start reading the databits array of the image from the end to the start; the problem is solved for that kind of images, but then, the images that did not have that problem, now appear upside down . how can I know how to read the databits array? how can I know if I have to read the databits array from the beginning to the end, or from the end of the array to the beginning, because I do not find any flag that tells me when to switch the order in how to read the databits array. friendly greetings Sign In·View Thread·PermaLink 3.50/5 (2 votes) What about MFC? bugDanny 10:38 22 Nov '05   Is this tutorial only for a Win 32 Application, or does it also apply to MFC? Danny The stupidity of others amazes me! Sign In·View Thread·PermaLink 2.50/5 (4 votes) an error while compiling ? dynamica123 8:21 4 Oct '05   When compiling the program , an error occured saying unexpected end of file while looking for precompiler header directive , i don't know how to solve this error ? Sign In·View Thread·PermaLink 1.75/5 (5 votes) Bitmap vikas amin 3:54 23 Aug '05   how do i save bitmap in a file and then display it back again , Vikas Amin Embin Technology Bombay vikas.amin@embin.com Sign In·View Thread·PermaLink 2.00/5 (7 votes) how can i store bitmap into memory? jags_vc 2:22 7 Mar '05   I want to capture the screen of active desktop so how can i get active desktop image into memory so that i can read it and transfer it to another Pc that will display that image ???? Any bady can suggest me how can it possible or if possible then give me sourcecode/link that will be helpful to me..... Sign In·View Thread·PermaLink 1.25/5 (4 votes) Re: how can i store bitmap into memory? Anonymous 12:34 4 Jun '05   Paint Shop Pro <-- google it it has the option to screen capture and saves as icons, bitmaps, and cursors <<< those are fun if you prefer bmps to other picture types i recommend a download of paint shop pro, it's free! Sign In·View Thread·PermaLink 1.00/5 (1 vote) Re: how can i store bitmap into memory? joyjjjz 20:50 4 Oct '08   very good， thanks Sign In·View Thread·PermaLink help for creating an image from 3 different RGB binary files sachin903 18:54 12 Jan '05   hi, actually i have 3 different binary files containing Red, blue and green values of a large image. i want to combine these values and get the 24 bit image by using pset Rgb or any other function. i have tried it for small image but it is not working for large images. if any one know this then please help me out ! Sign In·View Thread·PermaLink 2.00/5 (1 vote) Image data lost FJK 17:19 12 Dec '04   Starting, first of all thanks, I found the article great. I decided to learn more about this subject and is experimenting with printing of graphics. So what I do, get a printer DC, select createcompatible bitmap for the printer dc, select it into the dc and draw some lines and rectangles. Then I bitblt it to the printer - it all works. One step further, Before the above bitblt, I create a secons bitmap, and do the same process as with the first bitmap. Swaping the two bitmaps in and out, seems to be blackening them. In the begining of the article you mention that data might/is lost when resources get locked and unlocked. I assume this is what is happening here but you also mention win16. Can you tell me if I am making a mistake or is the graphics lost the moment you dc->select(olditmap) ? cheers Sign In·View Thread·PermaLink 2.00/5 (1 vote) Bitmap convertor vincentgoa3105 1:36 4 Dec '04   Hello Everyone, I am working on a Project in VC++ 6.0 and we are getting images of various sizes and image format in 8 bit monochrome. I wanted some code which would convert this 8 bit image to a 24 bit color image and also at the same time resize the image to a maximum size of 450 * 410 only. Any help including msdn references will do good. thanks Sign In·View Thread·PermaLink 2.25/5 (4 votes) help.....how do i load a 24-bitmap ??? rateep 21:06 18 Oct '04   well hello...i am new to vc++....and i seem to have a prob....i need to load a bitmap(24 bit).....but when itz loaded it getz converted to 16bit format???? why does that happen??? can anyone help me out??? my mail id is :rateep_jose@yahoo.co.uk thanx..... Sign In·View Thread·PermaLink 1.50/5 (2 votes) How to print bitmap, in a view/doc application goodmast3r 20:08 28 Sep '04   Bitmap is created in OnDraw. Thanks Work hard and a bit of luck is the key to success. Sign In·View Thread·PermaLink 1.50/5 (2 votes)

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