|
|
You're in the
dotnet drawing api
group:image graphics drawing confusion
dotnet drawing api:
why, in the AddEyeMarkers() method, both versions of the newImage object that I am saving don't contain ellipses that I have drawn using the Graphics.FromImage( newImage ) object. I expected newImage1.jpg to be the same size as m_originalImage, but with two ellipses drawn on it. I expected newImage2.jpg to be a thumbnail version of newImage1.jpg. Instead, newImage2.jpg is scaled thumbnail version, but missing the ellipses (In other words, a thumbnail version of m_originalImage ). How come? The overall mission is to get a scaled-down, eye-marked version of the original image, and stick it in a PictureBox on my form. Can anyone see what I am doing wrong? If this was to confusing to follow, let me know and I will try to rephrase my problem. Thanks, -cwineman /// Simply supposed to take an original image and create a scaled-down thumbnail version of the /// image that will fit in a PictureBox control. private Image AdjustImageSize( Image image ) { int maxSize = PICTURE_BOX_WIDTH; int oldWidth = image.Width; int oldHeight = image.Height; int newWidth = oldWidth; int newHeight = oldHeight; if( oldWidth > maxSize || oldHeight > maxSize ) { if( oldWidth > oldHeight ) { newWidth = maxSize; newHeight = (oldHeight * maxSize) / oldWidth; } else { newHeight = maxSize; newWidth = (oldWidth * maxSize) / oldHeight; } } return image.GetThumbnailImage( newWidth, newHeight, null, IntPtr.Zero ); } /// Makes a clone of original image(Since I don't want to mess up the original. /// Gets the graphics of the clone and draws some circles. (These circle represent eye /// positions) /// Save two different versions of newImage. /// Set the pictureBox control so that it shows original picture, but now adjusted to fit /// properly and now with eyes marked. private void AddEyeMarkers() { Image newImage = (Image) m_originalImage.Clone(); Pen pen = new Pen( Color.Red, 2f ); Graphics graphics = Graphics.FromImage( newImage ); graphics.DrawEllipse( pen, (_leftEye.X - 10), (_leftEye.Y - 10), 20, 20 ); graphics.DrawEllipse( pen, (_rightEye.X - 10), (_rightEye.Y - 10), 20, 20 ); newImage.Save( "c:\\temp\\newImage1.jpg", System.Drawing.Imaging.ImageFormat.Jpeg ); newImage = AdjustImageSize( newImage ); newImage.Save( "c:\\temp\\newImage2.jpg", System.Drawing.Imaging.ImageFormat.Jpeg ); pictureBox.Image = newImage; }
I think this problem comes from the fact that your AdjustImageSize routine
gets a thumbnail image. This isn't drawn from the bits you've modified but from the thumbnail that already exists in the jpeg file. Rather than use the GetThumbnailImage method, create your own thumbnail by drawing the image to a correctly sized memory bitmap. -- Bob Powell [MVP] Visual C#, System.Drawing The Image Transition Library wraps up and LED style instrumentation is available in the June of Well Formed for C# or VB programmers http://www.bobpowell.net/currentissue.htm Answer those GDI+ questions with the GDI+ FAQ http://www.bobpowell.net/gdiplus_faq.htm The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml Windows Forms Tips and Tricks RSS: http://www.bobpowell.net/tipstricks.xml Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml [quoted text, click to view] "cwineman" <me@home.com> wrote in message news:41095af4$1_2@127.0.0.1... > Below I list two methods that are part of my application. I don't understand > why, in the AddEyeMarkers() method, both versions of the newImage object > that I am saving don't contain ellipses that I have drawn using the > Graphics.FromImage( newImage ) object. > > I expected newImage1.jpg to be the same size as m_originalImage, but with > two ellipses drawn on it. I expected newImage2.jpg to be a thumbnail version > of newImage1.jpg. Instead, newImage2.jpg is scaled thumbnail version, but > missing the ellipses (In other words, a thumbnail version of > m_originalImage ). How come? > > The overall mission is to get a scaled-down, eye-marked version of the > original image, and stick it in a PictureBox on my form. > > Can anyone see what I am doing wrong? If this was to confusing to follow, > let me know and I will try to rephrase my problem. > > Thanks, > > -cwineman > > > /// Simply supposed to take an original image and create a scaled-down > thumbnail version of the /// image that will fit in a PictureBox control. > private Image AdjustImageSize( Image image ) > { > int maxSize = PICTURE_BOX_WIDTH; > int oldWidth = image.Width; > int oldHeight = image.Height; > int newWidth = oldWidth; > int newHeight = oldHeight; > > if( oldWidth > maxSize || oldHeight > maxSize ) > { > if( oldWidth > oldHeight ) > { > newWidth = maxSize; > newHeight = (oldHeight * maxSize) / oldWidth; > } > else > { > newHeight = maxSize; > newWidth = (oldWidth * maxSize) / oldHeight; > } > } > return image.GetThumbnailImage( newWidth, newHeight, null, IntPtr.Zero ); > } > > > /// Makes a clone of original image(Since I don't want to mess up the > original. > /// Gets the graphics of the clone and draws some circles. (These circle > represent eye > /// positions) > /// Save two different versions of newImage. > /// Set the pictureBox control so that it shows original picture, but now > adjusted to fit > /// properly and now with eyes marked. > private void AddEyeMarkers() > { > Image newImage = (Image) m_originalImage.Clone(); > Pen pen = new Pen( Color.Red, 2f ); > Graphics graphics = Graphics.FromImage( newImage ); > graphics.DrawEllipse( pen, (_leftEye.X - 10), (_leftEye.Y - 10), 20, 20 ); > graphics.DrawEllipse( pen, (_rightEye.X - 10), (_rightEye.Y - 10), 20, > 20 ); > > newImage.Save( "c:\\temp\\newImage1.jpg", > System.Drawing.Imaging.ImageFormat.Jpeg ); > > newImage = AdjustImageSize( newImage ); > newImage.Save( "c:\\temp\\newImage2.jpg", > System.Drawing.Imaging.ImageFormat.Jpeg ); > > pictureBox.Image = newImage; > } > >
I don't understand. I take an image, and write some ellipses on it. Fine.
Take that image and save it to disk and there it is with the ellipses drawn on it. Good. Now, take the same image and create a thumbnail version of it. Save it. Its a thumbnail, but there are no ellipses. Where did they go? If there are two different buffers how do I know which ones are going to get used in different method calls? The Save() method uses a buffer that has my modifications, but the GetThumbnailImage() doesn't? How does that make sense? How do I "create your own thumbnail by drawing the image to a correctly sized memory bitmap"? What methods do I use? Do you have a link to an example maybe? Thanks, -cwineman [quoted text, click to view] "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> wrote in message news:uIoJgDcdEHA.4092@TK2MSFTNGP10.phx.gbl... > I think this problem comes from the fact that your AdjustImageSize routine > gets a thumbnail image. This isn't drawn from the bits you've modified but > from the thumbnail that already exists in the jpeg file. > > Rather than use the GetThumbnailImage method, create your own thumbnail by > drawing the image to a correctly sized memory bitmap. > > -- > Bob Powell [MVP] > Visual C#, System.Drawing > > The Image Transition Library wraps up and LED style instrumentation is > available in the June of Well Formed for C# or VB programmers > http://www.bobpowell.net/currentissue.htm > > Answer those GDI+ questions with the GDI+ FAQ > http://www.bobpowell.net/gdiplus_faq.htm > > The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml > Windows Forms Tips and Tricks RSS: http://www.bobpowell.net/tipstricks.xml > Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml
Hmm. I'm not sure how it can have a pre-defined thumbnail. I dynamically
create a thumbnail of the size I desire. If there is a pre-difined thumbnail, how large is it? Wouldn't it get over-written? I've checked out your faq several times in trying to answer some of my imaging questions. One thing you might consider adding is something about how to load an image from a file buffer in memory. I had trouble with that, and it seems like something that would be a pretty common need for developers. I eventually had to use a bunch of COM calls (which I know nothing about) to load from an IStream. The code is below. Is there some easier way than that? Alot of people were saying I should write my own IStream implementation. Seems like a lot of work just to load an image from memory. Thanks for you help. Gdiplus::Bitmap * CSecurLinxImage::LoadBitmap( unsigned char * fileBuffer, int length ) { HGLOBAL m_hMem = GlobalAlloc( GMEM_FIXED, length ); BYTE* pmem = (BYTE*)GlobalLock(m_hMem); memcpy( pmem, fileBuffer, length ); IStream* pstm; CreateStreamOnHGlobal(m_hMem,FALSE,&pstm); Gdiplus::Bitmap * bitmap = Gdiplus::Bitmap::FromStream( pstm, FALSE ); GlobalUnlock( m_hMem ); pstm->Release(); return bitmap; } [quoted text, click to view] "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> wrote in message news:emlJytkdEHA.524@TK2MSFTNGP09.phx.gbl... > The GDI+ FAQ has articles on changing the resolution of an image and drawing > an image that will explain the process in more detail. Here's how to reduce > an image to 50% it's size... > > Bitmap bm=Bitmap.FromFile("myImage.bmp"); > Bitmap tmp=new Bitmap(bm.Width/2, bm.Height/2); > Graphics g=Graphics.FromImage(tmp); > g.DrawImage(bm,new > Rectangle(0,0,tmp.Width,tmp.Height),0,0,bm.Width,bm.Height,GraphicsUnit.Pixe > l); > g.Dispose(); > bm.Dispose(); > tmp.Save(......); // save the half-size file > > Some JPEG images have a pre-defined thumbnail. This would have been > generated before you modified the image. I'm assuming that you changed the > bits for the main image, saved the thing, including the old thumbnail and > when you extract the thumbnail the software decides to use the old, > unchanged bits of the supplementary image, not the new ones. > > > -- > Bob Powell [MVP] > Visual C#, System.Drawing > > The Image Transition Library wraps up and LED style instrumentation is > available in the June of Well Formed for C# or VB programmers > http://www.bobpowell.net/currentissue.htm > > Answer those GDI+ questions with the GDI+ FAQ > http://www.bobpowell.net/gdiplus_faq.htm > > The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml > Windows Forms Tips and Tricks RSS: http://www.bobpowell.net/tipstricks.xml > Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml
I still don't get it. Maybe I'm dense.I don't see how (or why) one of these
image objects could (would) have a second buffer for storing a thumbnail version of the original. What good would it do, since the thumbnail version is really a modification of the original, to the width/height that the caller wants? Anyway, I rewrote my resizing function to look similar to the code you had in your previous post. Now everything works just like a want.Thanks. I guess maybe your FAQ is only for managed .NET. I have used the System.IO.MemoryStream to create an image from a file buffer in memory. I keep getting confused because I am writing imaging code using GDI+ in managed and unmanaged code. What I was actually having problems with was loading an image from a buffer in unmanaged C++. There is a function Gdiplus::Bitmap::FromStream And it requires an IStream. I couldn't find an equivalent of System.IO.MemoryStream so I had to use all of those mysterious COM functions. So I guess I should ask you, in unmanaged C++, do you know of a better way to load a Bitmap from a file buffer in memory? I appreciate you help. Have a good weekend. [quoted text, click to view] "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> wrote in message news:uDgKVrmdEHA.2352@TK2MSFTNGP09.phx.gbl... > The point I'm trying to make is that if the original file had a thumbnail it > would be in a different part of the file structure and would look similar to > the original. Even though you changed the bits on the real image, maybe the > thumbnail bits didn't get changed. When you extracted the thumbnail again it > just gave you back the old, unaltered thumbnail stretched to whatever size > you asked for. > > I will certainly put an article in there for loading an image from a file > buffer in memory. I did something like this a while ago for a customer who > had a bitmap in a byte buffer. I handed the byte buffer to a memory stream > and read the file in from the memory stream. That might work as an > alternative to your CreateStreamOnHGlobal method. You can construct a memory > stream with a byte buffer and hand the memory stream to the FromStream > method. > -- > Bob Powell [MVP] > Visual C#, System.Drawing > > The Image Transition Library wraps up and LED style instrumentation is > available in the June of Well Formed for C# or VB programmers > http://www.bobpowell.net/currentissue.htm > > Answer those GDI+ questions with the GDI+ FAQ > http://www.bobpowell.net/gdiplus_faq.htm > > The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml > Windows Forms Tips and Tricks RSS: http://www.bobpowell.net/tipstricks.xml > Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml > > > > > > > "cwineman" <me@home.com> wrote in message news:410a7827$1_2@127.0.0.1... > > Hmm. I'm not sure how it can have a pre-defined thumbnail. I dynamically > > create a thumbnail of the size I desire. If there is a pre-difined > > thumbnail, how large is it? Wouldn't it get over-written? > > > > I've checked out your faq several times in trying to answer some of my > > imaging questions. One thing you might consider adding is something about > > how to load an image from a file buffer in memory. I had trouble with > that, > > and it seems like something that would be a pretty common need for > > developers. I eventually had to use a bunch of COM calls (which I know > > nothing about) to load from an IStream. The code is below. Is there some > > easier way than that? Alot of people were saying I should write my own > > IStream implementation. Seems like a lot of work just to load an image > from > > memory. > > > > Thanks for you help. > > > > Gdiplus::Bitmap * CSecurLinxImage::LoadBitmap( unsigned char * fileBuffer, > > int length ) > > > > { > > > > HGLOBAL m_hMem = GlobalAlloc( GMEM_FIXED, length ); > > > > BYTE* pmem = (BYTE*)GlobalLock(m_hMem); > > > > memcpy( pmem, fileBuffer, length ); > > > > IStream* pstm; > > > > CreateStreamOnHGlobal(m_hMem,FALSE,&pstm); > > > > Gdiplus::Bitmap * bitmap = Gdiplus::Bitmap::FromStream( pstm, FALSE ); > > > > GlobalUnlock( m_hMem ); > > > > pstm->Release(); > > > > return bitmap; > > > > } > > > > > > "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> wrote in message > > news:emlJytkdEHA.524@TK2MSFTNGP09.phx.gbl... > > > The GDI+ FAQ has articles on changing the resolution of an image and > > drawing > > > an image that will explain the process in more detail. Here's how to > > reduce > > > an image to 50% it's size... > > > > > > Bitmap bm=Bitmap.FromFile("myImage.bmp"); > > > Bitmap tmp=new Bitmap(bm.Width/2, bm.Height/2); > > > Graphics g=Graphics.FromImage(tmp); > > > g.DrawImage(bm,new > > > > > > Rectangle(0,0,tmp.Width,tmp.Height),0,0,bm.Width,bm.Height,GraphicsUnit.Pixe > > > l); > > > g.Dispose(); > > > bm.Dispose(); > > > tmp.Save(......); // save the half-size file > > > > > > Some JPEG images have a pre-defined thumbnail. This would have been > > > generated before you modified the image. I'm assuming that you changed > the > > > bits for the main image, saved the thing, including the old thumbnail > and > > > when you extract the thumbnail the software decides to use the old, > > > unchanged bits of the supplementary image, not the new ones. > > > > > > > > > -- > > > Bob Powell [MVP] > > > Visual C#, System.Drawing > > > > > > The Image Transition Library wraps up and LED style instrumentation is > > > available in the June of Well Formed for C# or VB programmers > > > http://www.bobpowell.net/currentissue.htm > > > > > > Answer those GDI+ questions with the GDI+ FAQ > > > http://www.bobpowell.net/gdiplus_faq.htm > > > > > > The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml > > > Windows Forms Tips and Tricks RSS: > http://www.bobpowell.net/tipstricks.xml > > > Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml > > > > > >
OK, a co-worker has explained something to me. I guess some jpg formats
store a thumbnail version of an image in their file structure. That is what you were talking about. Now, I don't think that explains what was going wrong. Even if I loaded my System.Drawing.Image object using one of these thumbnail-encapsulating jpg files, once it is loaded, it's independent of whatever file format it was loaded from. The Image object just has a buffer for the original image data, and wouldn't know about the thumbnail that may have been embeded in the jpg file. Right? So the GetThumbnailImage() function would always dynamically create a new image based on the original file content. [quoted text, click to view] "cwineman" <me@home.com> wrote in message news:410aad96$1_2@127.0.0.1... > I still don't get it. Maybe I'm dense.I don't see how (or why) one of these > image objects could (would) have a second buffer for storing a thumbnail > version of the original. What good would it do, since the thumbnail version > is really a modification of the original, to the width/height that the > caller wants? > > Anyway, I rewrote my resizing function to look similar to the code you had > in your previous post. Now everything works just like a want.Thanks. > > I guess maybe your FAQ is only for managed .NET. I have used the > System.IO.MemoryStream to create an image from a file buffer in memory. I > keep getting confused because I am writing imaging code using GDI+ in > managed and unmanaged code. What I was actually having problems with was > loading an image from a buffer in unmanaged C++. There is a function > Gdiplus::Bitmap::FromStream > > And it requires an IStream. I couldn't find an equivalent of > System.IO.MemoryStream so I had to use all of those mysterious COM > functions. So I guess I should ask you, in unmanaged C++, do you know of a > better way to load a Bitmap from a file buffer in memory? > > I appreciate you help. Have a good weekend. > > "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> wrote in message > news:uDgKVrmdEHA.2352@TK2MSFTNGP09.phx.gbl... > > The point I'm trying to make is that if the original file had a thumbnail > it > > would be in a different part of the file structure and would look similar > to > > the original. Even though you changed the bits on the real image, maybe > the > > thumbnail bits didn't get changed. When you extracted the thumbnail again > it > > just gave you back the old, unaltered thumbnail stretched to whatever size > > you asked for. > > > > I will certainly put an article in there for loading an image from a file > > buffer in memory. I did something like this a while ago for a customer who > > had a bitmap in a byte buffer. I handed the byte buffer to a memory stream > > and read the file in from the memory stream. That might work as an > > alternative to your CreateStreamOnHGlobal method. You can construct a > memory > > stream with a byte buffer and hand the memory stream to the FromStream > > method. > > -- > > Bob Powell [MVP] > > Visual C#, System.Drawing > > > > The Image Transition Library wraps up and LED style instrumentation is > > available in the June of Well Formed for C# or VB programmers > > http://www.bobpowell.net/currentissue.htm > > > > Answer those GDI+ questions with the GDI+ FAQ > > http://www.bobpowell.net/gdiplus_faq.htm > > > > The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml > > Windows Forms Tips and Tricks RSS: http://www.bobpowell.net/tipstricks.xml > > Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml
The GDI+ FAQ has articles on changing the resolution of an image and drawing
an image that will explain the process in more detail. Here's how to reduce an image to 50% it's size... Bitmap bm=Bitmap.FromFile("myImage.bmp"); Bitmap tmp=new Bitmap(bm.Width/2, bm.Height/2); Graphics g=Graphics.FromImage(tmp); g.DrawImage(bm,new Rectangle(0,0,tmp.Width,tmp.Height),0,0,bm.Width,bm.Height,GraphicsUnit.Pixe l); g.Dispose(); bm.Dispose(); tmp.Save(......); // save the half-size file Some JPEG images have a pre-defined thumbnail. This would have been generated before you modified the image. I'm assuming that you changed the bits for the main image, saved the thing, including the old thumbnail and when you extract the thumbnail the software decides to use the old, unchanged bits of the supplementary image, not the new ones. -- Bob Powell [MVP] Visual C#, System.Drawing The Image Transition Library wraps up and LED style instrumentation is available in the June of Well Formed for C# or VB programmers http://www.bobpowell.net/currentissue.htm Answer those GDI+ questions with the GDI+ FAQ http://www.bobpowell.net/gdiplus_faq.htm The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml Windows Forms Tips and Tricks RSS: http://www.bobpowell.net/tipstricks.xml Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml [quoted text, click to view] "cwineman" <me@home.com> wrote in message news:410a4ec8$1_2@127.0.0.1... > I don't understand. I take an image, and write some ellipses on it. Fine. > Take that image and save it to disk and there it is with the ellipses drawn > on it. Good. Now, take the same image and create a thumbnail version of it. > Save it. Its a thumbnail, but there are no ellipses. Where did they go? > > If there are two different buffers how do I know which ones are going to get > used in different method calls? The Save() method uses a buffer that has my > modifications, but the GetThumbnailImage() doesn't? How does that make > sense? > > How do I "create your own thumbnail by drawing the image to a correctly > sized memory bitmap"? What methods do I use? Do you have a link to an > example maybe? > > Thanks, > -cwineman > > > "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> wrote in message > news:uIoJgDcdEHA.4092@TK2MSFTNGP10.phx.gbl... > > I think this problem comes from the fact that your AdjustImageSize routine > > gets a thumbnail image. This isn't drawn from the bits you've modified but > > from the thumbnail that already exists in the jpeg file. > > > > Rather than use the GetThumbnailImage method, create your own thumbnail by > > drawing the image to a correctly sized memory bitmap. > > > > -- > > Bob Powell [MVP] > > Visual C#, System.Drawing > > > > The Image Transition Library wraps up and LED style instrumentation is > > available in the June of Well Formed for C# or VB programmers > > http://www.bobpowell.net/currentissue.htm > > > > Answer those GDI+ questions with the GDI+ FAQ > > http://www.bobpowell.net/gdiplus_faq.htm > > > > The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml > > Windows Forms Tips and Tricks RSS: http://www.bobpowell.net/tipstricks.xml > > Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml > >
The point I'm trying to make is that if the original file had a thumbnail it
would be in a different part of the file structure and would look similar to the original. Even though you changed the bits on the real image, maybe the thumbnail bits didn't get changed. When you extracted the thumbnail again it just gave you back the old, unaltered thumbnail stretched to whatever size you asked for. I will certainly put an article in there for loading an image from a file buffer in memory. I did something like this a while ago for a customer who had a bitmap in a byte buffer. I handed the byte buffer to a memory stream and read the file in from the memory stream. That might work as an alternative to your CreateStreamOnHGlobal method. You can construct a memory stream with a byte buffer and hand the memory stream to the FromStream method. -- Bob Powell [MVP] Visual C#, System.Drawing The Image Transition Library wraps up and LED style instrumentation is available in the June of Well Formed for C# or VB programmers http://www.bobpowell.net/currentissue.htm Answer those GDI+ questions with the GDI+ FAQ http://www.bobpowell.net/gdiplus_faq.htm The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml Windows Forms Tips and Tricks RSS: http://www.bobpowell.net/tipstricks.xml Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml [quoted text, click to view] "cwineman" <me@home.com> wrote in message news:410a7827$1_2@127.0.0.1... > Hmm. I'm not sure how it can have a pre-defined thumbnail. I dynamically > create a thumbnail of the size I desire. If there is a pre-difined > thumbnail, how large is it? Wouldn't it get over-written? > > I've checked out your faq several times in trying to answer some of my > imaging questions. One thing you might consider adding is something about > how to load an image from a file buffer in memory. I had trouble with that, > and it seems like something that would be a pretty common need for > developers. I eventually had to use a bunch of COM calls (which I know > nothing about) to load from an IStream. The code is below. Is there some > easier way than that? Alot of people were saying I should write my own > IStream implementation. Seems like a lot of work just to load an image from > memory. > > Thanks for you help. > > Gdiplus::Bitmap * CSecurLinxImage::LoadBitmap( unsigned char * fileBuffer, > int length ) > > { > > HGLOBAL m_hMem = GlobalAlloc( GMEM_FIXED, length ); > > BYTE* pmem = (BYTE*)GlobalLock(m_hMem); > > memcpy( pmem, fileBuffer, length ); > > IStream* pstm; > > CreateStreamOnHGlobal(m_hMem,FALSE,&pstm); > > Gdiplus::Bitmap * bitmap = Gdiplus::Bitmap::FromStream( pstm, FALSE ); > > GlobalUnlock( m_hMem ); > > pstm->Release(); > > return bitmap; > > } > > > "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> wrote in message > news:emlJytkdEHA.524@TK2MSFTNGP09.phx.gbl... > > The GDI+ FAQ has articles on changing the resolution of an image and > drawing > > an image that will explain the process in more detail. Here's how to > reduce > > an image to 50% it's size... > > > > Bitmap bm=Bitmap.FromFile("myImage.bmp"); > > Bitmap tmp=new Bitmap(bm.Width/2, bm.Height/2); > > Graphics g=Graphics.FromImage(tmp); > > g.DrawImage(bm,new > > > Rectangle(0,0,tmp.Width,tmp.Height),0,0,bm.Width,bm.Height,GraphicsUnit.Pixe > > l); > > g.Dispose(); > > bm.Dispose(); > > tmp.Save(......); // save the half-size file > > > > Some JPEG images have a pre-defined thumbnail. This would have been > > generated before you modified the image. I'm assuming that you changed the > > bits for the main image, saved the thing, including the old thumbnail and > > when you extract the thumbnail the software decides to use the old, > > unchanged bits of the supplementary image, not the new ones. > > > > > > -- > > Bob Powell [MVP] > > Visual C#, System.Drawing > > > > The Image Transition Library wraps up and LED style instrumentation is > > available in the June of Well Formed for C# or VB programmers > > http://www.bobpowell.net/currentissue.htm > > > > Answer those GDI+ questions with the GDI+ FAQ > > http://www.bobpowell.net/gdiplus_faq.htm > > > > The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml > > Windows Forms Tips and Tricks RSS: http://www.bobpowell.net/tipstricks.xml > > Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml > >
The thumbnails are stored as PropertyItems associated with the image. I
think it's possible that the thumbnail property item could be saved out again unchanged if it exists. Also, the GetThumbnail draws from the thumbnail PropertyItem if it exists and does not necessarily construct the thumbnail from the *real* image bits which is where I think your problem arises. -- Bob Powell [MVP] Visual C#, System.Drawing The Image Transition Library wraps up and LED style instrumentation is available in the June of Well Formed for C# or VB programmers http://www.bobpowell.net/currentissue.htm Answer those GDI+ questions with the GDI+ FAQ http://www.bobpowell.net/gdiplus_faq.htm The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml Windows Forms Tips and Tricks RSS: http://www.bobpowell.net/tipstricks.xml Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml [quoted text, click to view] "cwineman" <me@home.com> wrote in message news:410aafff$1_2@127.0.0.1... > OK, a co-worker has explained something to me. I guess some jpg formats > store a thumbnail version of an image in their file structure. That is what > you were talking about. > > Now, I don't think that explains what was going wrong. Even if I loaded my > System.Drawing.Image object using one of these thumbnail-encapsulating jpg > files, once it is loaded, it's independent of whatever file format it was > loaded from. The Image object just has a buffer for the original image data, > and wouldn't know about the thumbnail that may have been embeded in the jpg > file. Right? So the GetThumbnailImage() function would always dynamically > create a new image based on the original file content. > > > > "cwineman" <me@home.com> wrote in message news:410aad96$1_2@127.0.0.1... > > I still don't get it. Maybe I'm dense.I don't see how (or why) one of > these > > image objects could (would) have a second buffer for storing a thumbnail > > version of the original. What good would it do, since the thumbnail > version > > is really a modification of the original, to the width/height that the > > caller wants? > > > > Anyway, I rewrote my resizing function to look similar to the code you had > > in your previous post. Now everything works just like a want.Thanks. > > > > I guess maybe your FAQ is only for managed .NET. I have used the > > System.IO.MemoryStream to create an image from a file buffer in memory. I > > keep getting confused because I am writing imaging code using GDI+ in > > managed and unmanaged code. What I was actually having problems with was > > loading an image from a buffer in unmanaged C++. There is a function > > Gdiplus::Bitmap::FromStream > > > > And it requires an IStream. I couldn't find an equivalent of > > System.IO.MemoryStream so I had to use all of those mysterious COM > > functions. So I guess I should ask you, in unmanaged C++, do you know of a > > better way to load a Bitmap from a file buffer in memory? > > > > I appreciate you help. Have a good weekend. > > > > "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> wrote in message > > news:uDgKVrmdEHA.2352@TK2MSFTNGP09.phx.gbl... > > > The point I'm trying to make is that if the original file had a > thumbnail > > it > > > would be in a different part of the file structure and would look > similar > > to > > > the original. Even though you changed the bits on the real image, maybe > > the > > > thumbnail bits didn't get changed. When you extracted the thumbnail > again > > it > > > just gave you back the old, unaltered thumbnail stretched to whatever > size > > > you asked for. > > > > > > I will certainly put an article in there for loading an image from a > file > > > buffer in memory. I did something like this a while ago for a customer > who > > > had a bitmap in a byte buffer. I handed the byte buffer to a memory > stream > > > and read the file in from the memory stream. That might work as an > > > alternative to your CreateStreamOnHGlobal method. You can construct a > > memory > > > stream with a byte buffer and hand the memory stream to the FromStream > > > method. > > > -- > > > Bob Powell [MVP] > > > Visual C#, System.Drawing > > > > > > The Image Transition Library wraps up and LED style instrumentation is > > > available in the June of Well Formed for C# or VB programmers > > > http://www.bobpowell.net/currentissue.htm > > > > > > Answer those GDI+ questions with the GDI+ FAQ > > > http://www.bobpowell.net/gdiplus_faq.htm > > > > > > The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml > > > Windows Forms Tips and Tricks RSS: > http://www.bobpowell.net/tipstricks.xml > > > Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml > >
I actually haven't written any C++ for about 5 years... The FAQ does have a
bit of a managed code bias. Things will be changing on there very soon though and C++ will always be an important language. I will do something along those lines. To ensure that you see the articles I suggest you subscribe to the RSS feed for the FAQ. -- Bob Powell [MVP] Visual C#, System.Drawing The Image Transition Library wraps up and LED style instrumentation is available in the June of Well Formed for C# or VB programmers http://www.bobpowell.net/currentissue.htm Answer those GDI+ questions with the GDI+ FAQ http://www.bobpowell.net/gdiplus_faq.htm The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml Windows Forms Tips and Tricks RSS: http://www.bobpowell.net/tipstricks.xml Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml [quoted text, click to view] "cwineman" <me@home.com> wrote in message news:410aad96$1_2@127.0.0.1...
> I still don't get it. Maybe I'm dense.I don't see how (or why) one of these > image objects could (would) have a second buffer for storing a thumbnail > version of the original. What good would it do, since the thumbnail version > is really a modification of the original, to the width/height that the > caller wants? > > Anyway, I rewrote my resizing function to look similar to the code you had > in your previous post. Now everything works just like a want.Thanks. > > I guess maybe your FAQ is only for managed .NET. I have used the > System.IO.MemoryStream to create an image from a file buffer in memory. I > keep getting confused because I am writing imaging code using GDI+ in > managed and unmanaged code. What I was actually having problems with was > loading an image from a buffer in unmanaged C++. There is a function > Gdiplus::Bitmap::FromStream > > And it requires an IStream. I couldn't find an equivalent of > System.IO.MemoryStream so I had to use all of those mysterious COM > functions. So I guess I should ask you, in unmanaged C++, do you know of a > better way to load a Bitmap from a file buffer in memory? > > I appreciate you help. Have a good weekend. > > "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> wrote in message > news:uDgKVrmdEHA.2352@TK2MSFTNGP09.phx.gbl... > > The point I'm trying to make is that if the original file had a thumbnail > it > > would be in a different part of the file structure and would look similar > to > > the original. Even though you changed the bits on the real image, maybe > the > > thumbnail bits didn't get changed. When you extracted the thumbnail again > it > > just gave you back the old, unaltered thumbnail stretched to whatever size > > you asked for. > > > > I will certainly put an article in there for loading an image from a file > > buffer in memory. I did something like this a while ago for a customer who > > had a bitmap in a byte buffer. I handed the byte buffer to a memory stream > > and read the file in from the memory stream. That might work as an > > alternative to your CreateStreamOnHGlobal method. You can construct a > memory > > stream with a byte buffer and hand the memory stream to the FromStream > > method. > > -- > > Bob Powell [MVP] > > Visual C#, System.Drawing > > > > The Image Transition Library wraps up and LED style instrumentation is > > available in the June of Well Formed for C# or VB programmers > > http://www.bobpowell.net/currentissue.htm > > > > Answer those GDI+ questions with the GDI+ FAQ > > http://www.bobpowell.net/gdiplus_faq.htm > > > > The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml > > Windows Forms Tips and Tricks RSS: http://www.bobpowell.net/tipstricks.xml > > Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml > > > > > > > > > > > > > > "cwineman" <me@home.com> wrote in message news:410a7827$1_2@127.0.0.1... > > > Hmm. I'm not sure how it can have a pre-defined thumbnail. I dynamically > > > create a thumbnail of the size I desire. If there is a pre-difined > > > thumbnail, how large is it? Wouldn't it get over-written? > > > > > > I've checked out your faq several times in trying to answer some of my > > > imaging questions. One thing you might consider adding is something > about > > > how to load an image from a file buffer in memory. I had trouble with > > that, > > > and it seems like something that would be a pretty common need for > > > developers. I eventually had to use a bunch of COM calls (which I know > > > nothing about) to load from an IStream. The code is below. Is there some > > > easier way than that? Alot of people were saying I should write my own > > > IStream implementation. Seems like a lot of work just to load an image > > from > > > memory. > > > > > > Thanks for you help. > > > > > > Gdiplus::Bitmap * CSecurLinxImage::LoadBitmap( unsigned char * > fileBuffer, > > > int length ) > > > > > > { > > > > > > HGLOBAL m_hMem = GlobalAlloc( GMEM_FIXED, length ); > > > > > > BYTE* pmem = (BYTE*)GlobalLock(m_hMem); > > > > > > memcpy( pmem, fileBuffer, length ); > > > > > > IStream* pstm; > > > > > > CreateStreamOnHGlobal(m_hMem,FALSE,&pstm); > > > > > > Gdiplus::Bitmap * bitmap = Gdiplus::Bitmap::FromStream( pstm, FALSE ); > > > > > > GlobalUnlock( m_hMem ); > > > > > > pstm->Release(); > > > > > > return bitmap; > > > > > > } > > > > > > > > > "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> wrote in message > > > news:emlJytkdEHA.524@TK2MSFTNGP09.phx.gbl... > > > > The GDI+ FAQ has articles on changing the resolution of an image and > > > drawing > > > > an image that will explain the process in more detail. Here's how to > > > reduce > > > > an image to 50% it's size... > > > > > > > > Bitmap bm=Bitmap.FromFile("myImage.bmp"); > > > > Bitmap tmp=new Bitmap(bm.Width/2, bm.Height/2); > > > > Graphics g=Graphics.FromImage(tmp); > > > > g.DrawImage(bm,new > > > > > > > > > > Rectangle(0,0,tmp.Width,tmp.Height),0,0,bm.Width,bm.Height,GraphicsUnit.Pixe > > > > l); > > > > g.Dispose(); > > > > bm.Dispose(); > > > > tmp.Save(......); // save the half-size file > > > > > > > > Some JPEG images have a pre-defined thumbnail. This would have been > > > > generated before you modified the image. I'm assuming that you changed > > the > > > > bits for the main image, saved the thing, including the old thumbnail > > and > > > > when you extract the thumbnail the software decides to use the old, > > > > unchanged bits of the supplementary image, not the new ones. > > > > > > > > > > > > -- > > > > Bob Powell [MVP] > > > > Visual C#, System.Drawing > > > > > > > > The Image Transition Library wraps up and LED style instrumentation is > > > > available in the June of Well Formed for C# or VB programmers > > > > http://www.bobpowell.net/currentissue.htm > > > > > > > > Answer those GDI+ questions with the GDI+ FAQ > > > > http://www.bobpowell.net/gdiplus_faq.htm
Don't see what you're looking for? Try a search.
|
June 2003
July 2003
August 2003
September 2003
October 2003
November 2003
December 2003
January 2004
February 2004
March 2004
April 2004
May 2004
June 2004
July 2004
August 2004
September 2004
October 2004
November 2004
December 2004
January 2005
February 2005
March 2005
April 2005
May 2005
June 2005
July 2005
August 2005
September 2005
October 2005
November 2005
December 2005
January 2006
February 2006
March 2006
April 2006
May 2006
June 2006
July 2006
August 2006
September 2006
October 2006
November 2006
December 2006
January 2007
February 2007
March 2007
April 2007
May 2007
June 2007
July 2007
August 2007
September 2007
October 2007
November 2007
December 2007
January 2008
February 2008
March 2008
April 2008
May 2008
June 2008
| home · blog · groups | Questions? Comments? Contact the dn |