Get bytes from HBITMAP

Question

How can I get image bytes from hbitmap if I am given an HBITMAP pointer, and my application is console application. I tryed using GetDIBits which require such parameter as HDC, which I can't get.

EDIT: I load bitmap from file:

HBITMAP bm = 0; 
BITMAP Bitmap;
bm = (HBITMAP)LoadImage (0, TEXT("C:\\img1.bmp"), IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);

I pass the HBITMAP to the function and expect to get another HBITMAP of processed image:

HBITMAP out1 = func(bm);

Where func is:

HBITMAP func(HBITMAP im);

And the problem is how to get image bytes from HBITMAP.

Have you followed [Microsoft's Image Store](http://msdn.microsoft.com/en-us/library/dd145119%28v=VS.85%29.aspx) sample ? — WhozCraig, Jan 08 '13 at 03:09
@WhozCraig He stated that he tried `GetDIBits` but doesn't have a DC to pass to it (like the sample you linked to shows). — Jonathon Reinhart, Jan 08 '13 at 03:10
@JonathonReinhart Forgive my failure to link using GetDIBits() to the OP trying (and failing) to following the prescribed method of doing this task from Microsoft's website. I didn't make the connection, and apparently I should have. — WhozCraig, Jan 08 '13 at 03:18
I guess the real question here, is "What are you planning on doing with the raw bytes?" If you want to write them to a PNG image, or something, you *need* to be getting device-independent data with GetDIBits. — Jonathon Reinhart, Jan 08 '13 at 03:22
@Jonathon Reinhart I have to make some image processing and then output the result in a new HBITMAP pointer. — maximus, Jan 08 '13 at 04:31
@maximus The question at the end my answer stands -- "where did you get an `HBITMAP` without an accompanying `HDC`?" — Jonathon Reinhart, Jan 08 '13 at 04:33
@Jonathon Reinhart This is the specification of the function that I have to implement. I don't know where it comes from... — maximus, Jan 08 '13 at 04:35
@maximus Well your question doesn't make any sense then. See my edit. — Jonathon Reinhart, Jan 08 '13 at 04:41
@JonathonReinhart By the way, for testing purposes I am loading bitmap image using LoadImage function. And it comes without HDC — maximus, Jan 08 '13 at 05:08
@maximus I think you need to show your code. I can help no further without seeing what you're doing / trying to do. — Jonathon Reinhart, Jan 08 '13 at 05:20

score 14 · Answer 1 · edited Sep 27 '22 at 07:57

The easiest way is not to use GetDIBits (nor GetBitmapBits). These functions suck because they copy the data.
If you want the data directly, just use (for a DDB bitmap)

BITMAP bitmap;
GetObject(hBitmap, sizeof(bitmap), (LPVOID)&bitmap);

For a DIB bitmap use

DIBSECTION dib;
GetObject(hBitmap, sizeof(dib), (LPVOID)&dib);

GetObject info, See:
http://msdn.microsoft.com/en-us/library/windows/desktop/dd144904%28v=vs.85%29.aspx

This will not involve any copying of data, thus avoids the complicated issues associated with GetDIBits, See:
http://msdn.microsoft.com/en-us/library/windows/desktop/dd144879%28v=vs.85%29.aspx
Esp. the comments at the bottom for an explanation of the difficulties with GetDIBits.

Note that you do not get the palette info, but since most bitmaps are 24 or 32 bits anyway this is hardly an issue most of the time.

According to this https://msdn.microsoft.com/en-us/library/dd144904(v=vs.85).aspx if bitmap is not created by `CreateDIBSection` `bitmap.bmBit` pointer will be null. — Logman, Dec 12 '15 at 22:02

Jonathon Reinhart · Answer 2 · 2013-01-08T05:39:23.797

Since you're using LoadImage to get the HBITMAP, then it is indeed a DIB (Device-Independent Bitmap) (they call it a DIBsection). However, you don't have the color information.

This MSDN HOWTO shows you how to select the DIBsection into a memory DC. They then go on to use GetDIBColorTable to get the palette. However, I believe from there, with that DC you can use GetDIBits to get the RGB bitmap information as you were trying to do.

Here's the general gist of it:

// Create a memory DC and select the DIBSection into it
hMemDC = CreateCompatibleDC( NULL );
(HBITMAP)SelectObject( hMemDC, hBitmap );

GetDIBits(hMemDC, hBitmap, ...);

You'll note in their code that SelectObject returns a handle to the what was in the DC. They then restore that before calling DeleteDC. I'm not sure its entirely necessary, but they do it. I left it out here for clarity.

score 1 · Answer 3 · answered Jan 18 '17 at 13:59

What worked for us is this: call GetDIBits while the correct palette (if indexed colour) is still selected into the device context. (Without the palette selected, the colours got garbled.)

But in our use case, it turned out that DIB sections performed a lot better, so check those out as well and benchmark. However, there are some gotchas. Windows wouldn't use the palette, we had to call SetDIBColorTable before use. But the device context still needed a one entry (black only) dummy palette selected and realised into the device context otherwise Windows would also ignore the palette set by SetDIBColorTable. Both SetDIBColorTable and RealizePalette needed to be present otherwise the colours would be garbled.

Jonathon Reinhart · Accepted Answer · 2013-01-08T05:53:10.347

0

See new answer since question was edited...

You cannot do this without a handle to the device context (HDC). This is because GetDIBits expects an HBITMAP which is

A handle to the bitmap. This must be a compatible bitmap (DDB).

A DDB is a Device-Dependent Bitmap, (as opposed to a DIB, or Device-Independent Bitmap). That means:

Note that a DDB does not contain color values; instead, the colors are in a device-dependent format.

Which is why GetDIBits requires an HDC. Otherwise it cannot get the color information.

Perhaps a good question is, where did you get an HBITMAP without an accompanying HDC?

If you're trying to create this bitmap in memory, first you can call CreateCompatibleDC to create an in-memory DC compatible with some device, then CreateCompatibleBitmap with that DC. Then you have an HBITMAP and HDC to work with as you please. Otherwise, if you don't know what your HBITMAP is pointing to, you can't expect to do anything useful with it.

edited Jan 08 '13 at 05:53

answered Jan 08 '13 at 03:14

Jonathon Reinhart

132,704
33
254
328

Do you mean that anyway if using HBITMAP pointer I will have to deal with HDC? – maximus Jan 08 '13 at 03:16
If you want to get color information, yes. Look at the link I included on DDBs. – Jonathon Reinhart Jan 08 '13 at 03:18
1

Only if you are dealing with a **DDB**, which is dependant on an `HDC`. If you are dealing with a **DIB** instead, then you do not need an `HDC`. So what does your `HBITMAP` actually point to - a **DDB** or a **DIB**? – Remy Lebeau Jan 08 '13 at 03:22
@RemyLebeau I thought an `HBITMAP` was always a **DDB**. [`HBITMAP` on MSDN](http://msdn.microsoft.com/en-us/library/windows/desktop/aa383751(v=vs.85).aspx) points you to [this](http://msdn.microsoft.com/en-us/library/windows/desktop/dd183377(v=vs.85).aspx) page, after which [About Bitmaps](http://msdn.microsoft.com/en-us/library/windows/desktop/dd162461(v=vs.85).aspx) states "**A bitmap is one of the GDI objects that can be selected into a device context (DC)**" – Jonathon Reinhart Jan 08 '13 at 03:26
@Jonathon Reinhart So it is not possible to connect existing HBITMAP with a newly created with HDC as you described in the Edit to your answer? – maximus Jan 08 '13 at 04:49
Like I said, (unless I'm wrong, @RemyLebeau?) an `HBITMAP` is already tied to an `HDC`, in the extent that the `HDC` has the color information that the `HBITMAP` is referring to. You can certainly try, but I don't expect it to work. Again, your `HBITMAP` has to be coming from *somewhere* - and most likely, that place has its `HDC`. – Jonathon Reinhart Jan 08 '13 at 04:51
@Jonathon Reinhart if the HBITMAP was created using HDC, won't the GetDC function return the needed HDC if my function is called from DLL? – maximus Jan 08 '13 at 06:28
@maximus Did you look at the documentation for `GetDC`? It takes an `HWND` to a window. The `HBITMAP` you're getting from `LoadImage` has nothing to do with your window (if you even have one). – Jonathon Reinhart Jan 08 '13 at 06:31
@Jonathon Reinhart I mean in case if HBITMAP was retrieved not using LoadImage. What if I pass NULL to getdc or GetCompatibleDC. Are you sure it is impossible to do something if HDC not provided? – maximus Jan 08 '13 at 06:35
@Jonathon Reinhart OK I checked it, it is enough to call GetDC(NULL) and it works with it. – maximus Jan 08 '13 at 07:53
Like I've said, it all depends where the HBITMAP is coming from, and if it's a DDB or DIB. I've given you everything I know and then some. – Jonathon Reinhart Jan 08 '13 at 08:07
If you load a bitmap from a resource, then you get an `HBITMAP`, but it's not tied to a particular DC. Like Remy has said, it is loading a DIB, not a DDB, so no DC is required. – Cody Gray - on strike Feb 06 '16 at 13:18

score 0 · Answer 5 · answered Jan 08 '13 at 03:18

0

You can try GetBitmapBits API even from console. More here: http://msdn.microsoft.com/en-us/library/windows/desktop/dd144850%28v=vs.85%29.aspx

Just pass HBITMAP handle and you'll get your bytes

answered Jan 08 '13 at 03:18

Vahid Farahmand

2,528
2
14
20

From MSDN: "'**Note** This function is provided only for compatibility with 16-bit versions of Windows. Applications should use the [**GetDIBits**](http://msdn.microsoft.com/en-us/library/windows/desktop/dd144879.aspx) function." – Jonathon Reinhart Jan 08 '13 at 03:19
Furthermore, this is getting the raw bits, but it is *still* a device-dependent bitmap, so you don't have correct color information. – Jonathon Reinhart Jan 08 '13 at 03:20
see my latest comment on the OP. – Jonathon Reinhart Jan 08 '13 at 03:22
@Vahid Farahmand GetBitmapBits is returning 0. Which means fail. – maximus Jan 08 '13 at 04:54

Get bytes from HBITMAP

5 Answers5

Linked

Related