BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Re-combining two bitmaps from delta image Goto page 1, 2  Next          BorlandTalk.com Forum Index -> Delphi Graphics View previous topic :: View next topic   Author Message dave Guest Posted: Sun Feb 05, 2006 6:01 pm    Post subject: Re-combining two bitmaps from delta image Hi I have bitmap A, which I have 'painted' a thick blue line upon using a paint program and added some white text, to make bitmap B. I thought I had worked out how to get the delta bitmap B-A, that is the difference between two other bitmaps. But now I want to 'recombine' the delta bitmap with the bitmap A onscrean to obtain bitmap B's image I'm getting problems. My delta image is mostly black with an area showing the original image, but different colours, where the blue line is. The white text of image B looks brown. On efg2.com it said the fastest way to combine images for the screen was to blit them. With dwRop set to SrcPaint, the new combined image has the white text, but the thick blue line has some blue in but is mostly white too. Not sure what I'm missing so any help will be appreciated Thanks Back to top Mr. X Guest Posted: Mon Feb 06, 2006 1:02 pm    Post subject: Re: Re-combining two bitmaps from delta image you can experiment with other rops but using scanline to merge both bitmaps (in 24bit format) is the best way "dave" <deepthinker (AT) btinternet (DOT) com> wrote in message news:43e635f7$1 (AT) newsgroups (DOT) borland.com... Quote: Hi I have bitmap A, which I have 'painted' a thick blue line upon using a paint program and added some white text, to make bitmap B. I thought I had worked out how to get the delta bitmap B-A, that is the difference between two other bitmaps. But now I want to 'recombine' the delta bitmap with the bitmap A onscrean to obtain bitmap B's image I'm getting problems. Quote: My delta image is mostly black with an area showing the original image, but different colours, where the blue line is. The white text of image B looks brown. Quote: On efg2.com it said the fastest way to combine images for the screen was to blit them. With dwRop set to SrcPaint, the new combined image has the white text, but the thick blue line has some blue in but is mostly white too. Quote: Not sure what I'm missing so any help will be appreciated Thanks Back to top dave Guest Posted: Mon Feb 06, 2006 3:02 pm    Post subject: Re: Re-combining two bitmaps from delta image Hi I experimented with them all and non of them resulted in looking like image B. I thought maybe I needed to do some combination or produce the delta image in a different way. Im I correct in my understanding that bliting it should be faster as its the graphics card that does the work, freeing up the cpu? I must admit thats not what was appearing to happen in a test app i wrote, the bitblt command seemed to take longer to return from, than the procedure that created the delta image. Admitedly i was only calculating the time it took for a small bitmap. If I recombine using scanline is it a simple matter of changing the '-' to '+' ? Thanks for the help "Mr. X" <no (AT) mail (DOT) here> wrote: Quote: you can experiment with other rops but using scanline to merge both bitmaps (in 24bit format) is the best way "dave" <deepthinker (AT) btinternet (DOT) com> wrote in message news:43e635f7$1 (AT) newsgroups (DOT) borland.com... Hi I have bitmap A, which I have 'painted' a thick blue line upon using a paint program and added some white text, to make bitmap B. I thought I had worked out how to get the delta bitmap B-A, that is the difference between two other bitmaps. But now I want to 'recombine' the delta bitmap with the bitmap A onscrean to obtain bitmap B's image I'm getting problems. My delta image is mostly black with an area showing the original image, but different colours, where the blue line is. The white text of image B looks brown. On efg2.com it said the fastest way to combine images for the screen was to blit them. With dwRop set to SrcPaint, the new combined image has the white text, but the thick blue line has some blue in but is mostly white too. Not sure what I'm missing so any help will be appreciated Thanks Back to top Francesco Savastano Guest Posted: Mon Feb 06, 2006 3:02 pm    Post subject: Re: Re-combining two bitmaps from delta image Please show your code if you want more help: Maybe for you it's enough clear but I was not able to und well what you're trying to do "dave" <deepthinker (AT) btinternet (DOT) com> ha scritto nel messaggio news:43e635f7$1 (AT) newsgroups (DOT) borland.com... Quote: Hi I have bitmap A, which I have 'painted' a thick blue line upon using a paint program and added some white text, to make bitmap B. I thought I had worked out how to get the delta bitmap B-A, that is the difference between two other bitmaps. But now I want to 'recombine' the delta bitmap with the bitmap A onscrean to obtain bitmap B's image I'm getting problems. My delta image is mostly black with an area showing the original image, but different colours, where the blue line is. The white text of image B looks brown. On efg2.com it said the fastest way to combine images for the screen was to blit them. With dwRop set to SrcPaint, the new combined image has the white text, but the thick blue line has some blue in but is mostly white too. Not sure what I'm missing so any help will be appreciated Thanks Back to top Francesco Savastano Guest Posted: Mon Feb 06, 2006 6:02 pm    Post subject: Re: Re-combining two bitmaps from delta image I didn't look too deep in your problem but AFAIU your approuch to the problem is too simplicistic. In a mathematical operation you can do C := B - A and then B := A + C but did you think about this: what happens if B - A is less than 0? The pixels in a bitmap cannot contain negative values and you are using a bitmap as container for the difference. You need a different container for the delta values which supports negative values, for example you could use an array.. Also I don't see the need to use 32bit pixel format, just use 24bit since I am assuming you are not using alpha channel if you are blitting on a form canvas. Hope it helps Francesco "dave" <deepthinker (AT) btinternet (DOT) com> ha scritto nel messaggio news:43e77f90$1 (AT) newsgroups (DOT) borland.com... Quote: Hi This is how I'm getting the delta image: function createDelta(original:TBitMap;new: TBitMap): TBitMap; var x,row : Integer; delta : TBitMap; PtrOrigRow,PtrNewRow : PByte; y : Integer; LineO,lineN,LineD : PRGB32Array; begin delta:= TBitMap.create; delta.TransparentColor:=original.TransparentColor; delta.TransparentMode:=original.TransparentMode; delta.Palette:=original.Palette; original.PixelFormat:=pf32bit; new.PixelFormat:=pf32bit; delta.PixelFormat:=pf32bit; delta.Height:=original.Height; delta.Width:=original.Width; for y := 0 to original.Height - 1 do begin LineO := original.Scanline[y]; LineN := new.Scanline[y]; LineD := delta.Scanline[y]; for x := 0 to original.Width - 1 do begin LineD[x].B:=LineN[x].B -LineO[x].B; LineD[x].G:=LineN[x].G -LineO[x].G; LineD[x].R:=LineN[x].R -LineO[x].R; LineD[x].A:=LineN[x].A -LineO[x].A; end; end; result:=delta; end; I then try recombining using: bitblt(form1.Canvas.Handle,x,y,im2.Width,im2.Height,im2.Canvas.Handle,0,0,SrcPaint ) where im2 is the tbitmap returned from the first function. thanks "Francesco Savastano" <francosavastano (AT) TakeThisOutFromAddress (DOT) virgilio.it wrote: Please show your code if you want more help: Maybe for you it's enough clear but I was not able to und well what you're trying to do "dave" <deepthinker (AT) btinternet (DOT) com> ha scritto nel messaggio news:43e635f7$1 (AT) newsgroups (DOT) borland.com... Hi I have bitmap A, which I have 'painted' a thick blue line upon using a paint program and added some white text, to make bitmap B. I thought I had worked out how to get the delta bitmap B-A, that is the difference between two other bitmaps. But now I want to 'recombine' the delta bitmap with the bitmap A onscrean to obtain bitmap B's image I'm getting problems. My delta image is mostly black with an area showing the original image, but different colours, where the blue line is. The white text of image B looks brown. On efg2.com it said the fastest way to combine images for the screen was to blit them. With dwRop set to SrcPaint, the new combined image has the white text, but the thick blue line has some blue in but is mostly white too. Not sure what I'm missing so any help will be appreciated Thanks Back to top dave Guest Posted: Mon Feb 06, 2006 6:02 pm    Post subject: Re: Re-combining two bitmaps from delta image Hi This is how I'm getting the delta image: function createDelta(original:TBitMap;new: TBitMap): TBitMap; var x,row : Integer; delta : TBitMap; PtrOrigRow,PtrNewRow : PByte; y : Integer; LineO,lineN,LineD : PRGB32Array; begin delta:= TBitMap.create; delta.TransparentColor:=original.TransparentColor; delta.TransparentMode:=original.TransparentMode; delta.Palette:=original.Palette; original.PixelFormat:=pf32bit; new.PixelFormat:=pf32bit; delta.PixelFormat:=pf32bit; delta.Height:=original.Height; delta.Width:=original.Width; for y := 0 to original.Height - 1 do begin LineO := original.Scanline[y]; LineN := new.Scanline[y]; LineD := delta.Scanline[y]; for x := 0 to original.Width - 1 do begin LineD[x].B:=LineN[x].B -LineO[x].B; LineD[x].G:=LineN[x].G -LineO[x].G; LineD[x].R:=LineN[x].R -LineO[x].R; LineD[x].A:=LineN[x].A -LineO[x].A; end; end; result:=delta; end; I then try recombining using: bitblt(form1.Canvas.Handle,x,y,im2.Width,im2.Height,im2.Canvas.Handle,0,0,SrcPaint ) where im2 is the tbitmap returned from the first function. thanks "Francesco Savastano" <francosavastano (AT) TakeThisOutFromAddress (DOT) virgilio.it> wrote: Quote: Please show your code if you want more help: Maybe for you it's enough clear but I was not able to und well what you're trying to do "dave" <deepthinker (AT) btinternet (DOT) com> ha scritto nel messaggio news:43e635f7$1 (AT) newsgroups (DOT) borland.com... Hi I have bitmap A, which I have 'painted' a thick blue line upon using a paint program and added some white text, to make bitmap B. I thought I had worked out how to get the delta bitmap B-A, that is the difference between two other bitmaps. But now I want to 'recombine' the delta bitmap with the bitmap A onscrean to obtain bitmap B's image I'm getting problems. My delta image is mostly black with an area showing the original image, but different colours, where the blue line is. The white text of image B looks brown. On efg2.com it said the fastest way to combine images for the screen was to blit them. With dwRop set to SrcPaint, the new combined image has the white text, but the thick blue line has some blue in but is mostly white too. Not sure what I'm missing so any help will be appreciated Thanks Back to top dave Guest Posted: Mon Feb 06, 2006 8:03 pm    Post subject: Re: Re-combining two bitmaps from delta image Hi Hmm I think you are right, I hadn't thought it through. In a previous post Nils had talked about the delta image being B-A. I have been searching for information on this for a few days with out finding any code examples, or much else. The idea was to reduce the time involved in transmitting consecutive screengrabs by working out the difference, encode to remove the 0's and transmit it where it could be 'recreated' on the another pc. So should I/can I use the delta bitmap as a mask to 'remove' the non modified pixels and transmitting that? Thanks for any help given D "Francesco Savastano" <francosavastano (AT) TakeThisOutFromAddress (DOT) virgilio.it> wrote: Quote: I didn't look too deep in your problem but AFAIU your approuch to the problem is too simplicistic. In a mathematical operation you can do C := B - A and then B := A + C but did you think about this: what happens if B - A is less than 0? The pixels in a bitmap cannot contain negative values and you are using a bitmap as container for the difference. You need a different container for the delta values which supports negative values, for example you could use an array.. Also I don't see the need to use 32bit pixel format, just use 24bit since I am assuming you are not using alpha channel if you are blitting on a form canvas. Hope it helps Francesco "dave" <deepthinker (AT) btinternet (DOT) com> ha scritto nel messaggio news:43e77f90$1 (AT) newsgroups (DOT) borland.com... Hi This is how I'm getting the delta image: function createDelta(original:TBitMap;new: TBitMap): TBitMap; var x,row : Integer; delta : TBitMap; PtrOrigRow,PtrNewRow : PByte; y : Integer; LineO,lineN,LineD : PRGB32Array; begin delta:= TBitMap.create; delta.TransparentColor:=original.TransparentColor; delta.TransparentMode:=original.TransparentMode; delta.Palette:=original.Palette; original.PixelFormat:=pf32bit; new.PixelFormat:=pf32bit; delta.PixelFormat:=pf32bit; delta.Height:=original.Height; delta.Width:=original.Width; for y := 0 to original.Height - 1 do begin LineO := original.Scanline[y]; LineN := new.Scanline[y]; LineD := delta.Scanline[y]; for x := 0 to original.Width - 1 do begin LineD[x].B:=LineN[x].B -LineO[x].B; LineD[x].G:=LineN[x].G -LineO[x].G; LineD[x].R:=LineN[x].R -LineO[x].R; LineD[x].A:=LineN[x].A -LineO[x].A; end; end; result:=delta; end; I then try recombining using: bitblt(form1.Canvas.Handle,x,y,im2.Width,im2.Height,im2.Canvas.Handle,0,0,SrcPaint ) where im2 is the tbitmap returned from the first function. thanks "Francesco Savastano" <francosavastano (AT) TakeThisOutFromAddress (DOT) virgilio.it wrote: Please show your code if you want more help: Maybe for you it's enough clear but I was not able to und well what you're trying to do "dave" <deepthinker (AT) btinternet (DOT) com> ha scritto nel messaggio news:43e635f7$1 (AT) newsgroups (DOT) borland.com... Hi I have bitmap A, which I have 'painted' a thick blue line upon using a paint program and added some white text, to make bitmap B. I thought I had worked out how to get the delta bitmap B-A, that is the difference between two other bitmaps. But now I want to 'recombine' the delta bitmap with the bitmap A onscrean to obtain bitmap B's image I'm getting problems. My delta image is mostly black with an area showing the original image, but different colours, where the blue line is. The white text of image B looks brown. On efg2.com it said the fastest way to combine images for the screen was to blit them. With dwRop set to SrcPaint, the new combined image has the white text, but the thick blue line has some blue in but is mostly white too. Not sure what I'm missing so any help will be appreciated Thanks Back to top Rimvydas Paulavicius Guest Posted: Tue Feb 07, 2006 6:02 am    Post subject: Re: Re-combining two bitmaps from delta image You could use xor instead of +- operations. Rimvydas Francesco Savastano wrote: Quote: I didn't look too deep in your problem but AFAIU your approuch to the problem is too simplicistic. In a mathematical operation you can do C := B - A and then B := A + C but did you think about this: what happens if B - A is less than 0? The pixels in a bitmap cannot contain negative values and you are using a bitmap as container for the difference. You need a different container for the delta values which supports negative values, for example you could use an array.. Also I don't see the need to use 32bit pixel format, just use 24bit since I am assuming you are not using alpha channel if you are blitting on a form canvas. Hope it helps Francesco "dave" <deepthinker (AT) btinternet (DOT) com> ha scritto nel messaggio news:43e77f90$1 (AT) newsgroups (DOT) borland.com... Hi This is how I'm getting the delta image: function createDelta(original:TBitMap;new: TBitMap): TBitMap; var x,row : Integer; delta : TBitMap; PtrOrigRow,PtrNewRow : PByte; y : Integer; LineO,lineN,LineD : PRGB32Array; begin delta:= TBitMap.create; delta.TransparentColor:=original.TransparentColor; delta.TransparentMode:=original.TransparentMode; delta.Palette:=original.Palette; original.PixelFormat:=pf32bit; new.PixelFormat:=pf32bit; delta.PixelFormat:=pf32bit; delta.Height:=original.Height; delta.Width:=original.Width; for y := 0 to original.Height - 1 do begin LineO := original.Scanline[y]; LineN := new.Scanline[y]; LineD := delta.Scanline[y]; for x := 0 to original.Width - 1 do begin LineD[x].B:=LineN[x].B -LineO[x].B; LineD[x].G:=LineN[x].G -LineO[x].G; LineD[x].R:=LineN[x].R -LineO[x].R; LineD[x].A:=LineN[x].A -LineO[x].A; end; end; result:=delta; end; I then try recombining using: bitblt(form1.Canvas.Handle,x,y,im2.Width,im2.Height,im2.Canvas.Handle,0,0,SrcPaint ) where im2 is the tbitmap returned from the first function. thanks "Francesco Savastano" <francosavastano (AT) TakeThisOutFromAddress (DOT) virgilio.it wrote: Please show your code if you want more help: Maybe for you it's enough clear but I was not able to und well what you're trying to do "dave" <deepthinker (AT) btinternet (DOT) com> ha scritto nel messaggio news:43e635f7$1 (AT) newsgroups (DOT) borland.com... Hi I have bitmap A, which I have 'painted' a thick blue line upon using a paint program and added some white text, to make bitmap B. I thought I had worked out how to get the delta bitmap B-A, that is the difference between two other bitmaps. But now I want to 'recombine' the delta bitmap with the bitmap A onscrean to obtain bitmap B's image I'm getting problems. My delta image is mostly black with an area showing the original image, but different colours, where the blue line is. The white text of image B looks brown. On efg2.com it said the fastest way to combine images for the screen was to blit them. With dwRop set to SrcPaint, the new combined image has the white text, but the thick blue line has some blue in but is mostly white too. Not sure what I'm missing so any help will be appreciated Thanks Back to top Francesco Savastano Guest Posted: Tue Feb 07, 2006 12:02 pm    Post subject: Re: Re-combining two bitmaps from delta image I don't know but maybe the solution can be rather simple: Just check each pixel if it's changed, then put the changed pixel into an array and transmit them type TTransmittedPixel= record rgb: tcolor; pos: TPoint; end; the recieving computer will then apply the changed pixels on top of other picture. -- New World Software Creative Tools for Creative People http://new-world-software.com "dave" <deepthinker (AT) btinternet (DOT) com> ha scritto nel messaggio news:43e7a444$1 (AT) newsgroups (DOT) borland.com... Quote: Hi Hmm I think you are right, I hadn't thought it through. In a previous post Nils had talked about the delta image being B-A. I have been searching for information on this for a few days with out finding any code examples, or much else. The idea was to reduce the time involved in transmitting consecutive screengrabs by working out the difference, encode to remove the 0's and transmit it where it could be 'recreated' on the another pc. So should I/can I use the delta bitmap as a mask to 'remove' the non modified pixels and transmitting that? Thanks for any help given D "Francesco Savastano" <francosavastano (AT) TakeThisOutFromAddress (DOT) virgilio.it wrote: I didn't look too deep in your problem but AFAIU your approuch to the problem is too simplicistic. In a mathematical operation you can do C := B - A and then B := A + C but did you think about this: what happens if B - A is less than 0? The pixels in a bitmap cannot contain negative values and you are using a bitmap as container for the difference. You need a different container for the delta values which supports negative values, for example you could use an array.. Also I don't see the need to use 32bit pixel format, just use 24bit since I am assuming you are not using alpha channel if you are blitting on a form canvas. Hope it helps Francesco "dave" <deepthinker (AT) btinternet (DOT) com> ha scritto nel messaggio news:43e77f90$1 (AT) newsgroups (DOT) borland.com... Hi This is how I'm getting the delta image: function createDelta(original:TBitMap;new: TBitMap): TBitMap; var x,row : Integer; delta : TBitMap; PtrOrigRow,PtrNewRow : PByte; y : Integer; LineO,lineN,LineD : PRGB32Array; begin delta:= TBitMap.create; delta.TransparentColor:=original.TransparentColor; delta.TransparentMode:=original.TransparentMode; delta.Palette:=original.Palette; original.PixelFormat:=pf32bit; new.PixelFormat:=pf32bit; delta.PixelFormat:=pf32bit; delta.Height:=original.Height; delta.Width:=original.Width; for y := 0 to original.Height - 1 do begin LineO := original.Scanline[y]; LineN := new.Scanline[y]; LineD := delta.Scanline[y]; for x := 0 to original.Width - 1 do begin LineD[x].B:=LineN[x].B -LineO[x].B; LineD[x].G:=LineN[x].G -LineO[x].G; LineD[x].R:=LineN[x].R -LineO[x].R; LineD[x].A:=LineN[x].A -LineO[x].A; end; end; result:=delta; end; I then try recombining using: bitblt(form1.Canvas.Handle,x,y,im2.Width,im2.Height,im2.Canvas.Handle,0,0,SrcPaint ) where im2 is the tbitmap returned from the first function. thanks "Francesco Savastano" francosavastano (AT) TakeThisOutFromAddress (DOT) virgilio.it wrote: Please show your code if you want more help: Maybe for you it's enough clear but I was not able to und well what you're trying to do "dave" <deepthinker (AT) btinternet (DOT) com> ha scritto nel messaggio news:43e635f7$1 (AT) newsgroups (DOT) borland.com... Hi I have bitmap A, which I have 'painted' a thick blue line upon using a paint program and added some white text, to make bitmap B. I thought I had worked out how to get the delta bitmap B-A, that is the difference between two other bitmaps. But now I want to 'recombine' the delta bitmap with the bitmap A onscrean to obtain bitmap B's image I'm getting problems. My delta image is mostly black with an area showing the original image, but different colours, where the blue line is. The white text of image B looks brown. On efg2.com it said the fastest way to combine images for the screen was to blit them. With dwRop set to SrcPaint, the new combined image has the white text, but the thick blue line has some blue in but is mostly white too. Not sure what I'm missing so any help will be appreciated Thanks Back to top Jens Gruschel Guest Posted: Tue Feb 07, 2006 6:02 pm    Post subject: Re: Re-combining two bitmaps from delta image Quote: You could use xor instead of +- operations. While xor also results in 0 if both values are identical, I'd use +-, because slightly different colors result in small values (127 xor 128 is 255). If you and the result with 255 it should be possible to undo the operation without problems. Jens -- Jens Gruschel http://www.pegtop.net Back to top Lord Crc Guest Posted: Tue Feb 07, 2006 7:01 pm    Post subject: Re: Re-combining two bitmaps from delta image On Mon, 6 Feb 2006 18:56:08 +0100, "Francesco Savastano" <francosavastano (AT) TakeThisOutFromAddress (DOT) virgilio.it> wrote: Quote: In a mathematical operation you can do C := B - A and then B := A + C but did you think about this: what happens if B - A is less than 0? Imagine A = 50, B = 20. Then you get C = -30. However, since C is stored as a byte, and the processor works in two's complement mode, this is stored as to 226. When you later perform A + C, the result is 276. This is however larger than 256, and only the lower 8 bits are stored in the byte B, which results in B = 20. So you can perfectly well store a difference of two byte's in a byte, and reconstruct it. - Asbjørn Back to top Francesco Savastano Guest Posted: Tue Feb 07, 2006 11:02 pm    Post subject: Re: Re-combining two bitmaps from delta image anyway it's never good to hit the limits..and where something is too strangely implemented I highly suspect there are better and easier ways to do it. As I already mentioned I don't see why he needs to do the difference of 2 bitmaps: all he needs is to detect if 2 pixel are the same or differ of any amount and store them into a stream to send to another computer. IMHO If he creates a 3rd bitmap it is only a waste of memory.. The delta bitmap is as large as the original bitmap so makes no sense to create it. he just needs to send the minimum amount of informations necessary to see the changes on another ocmputer. "Lord Crc" <lordcrc (AT) hotmail (DOT) com> ha scritto nel messaggio news:bhphu191j5pe655b9f6br27h7u69138ui5 (AT) 4ax (DOT) com... Quote: On Mon, 6 Feb 2006 18:56:08 +0100, "Francesco Savastano" francosavastano (AT) TakeThisOutFromAddress (DOT) virgilio.it> wrote: In a mathematical operation you can do C := B - A and then B := A + C but did you think about this: what happens if B - A is less than 0? Imagine A = 50, B = 20. Then you get C = -30. However, since C is stored as a byte, and the processor works in two's complement mode, this is stored as to 226. When you later perform A + C, the result is 276. This is however larger than 256, and only the lower 8 bits are stored in the byte B, which results in B = 20. So you can perfectly well store a difference of two byte's in a byte, and reconstruct it. - Asbjørn Back to top Jens Gruschel Guest Posted: Wed Feb 08, 2006 12:04 am    Post subject: Re: Re-combining two bitmaps from delta image Quote: anyway it's never good to hit the limits.. Why not? Quote: As I already mentioned I don't see why he needs to do the difference of 2 bitmaps If he has the difference, he can use a better compression. Well, I don't know about typical screen images (probably it depends on what applications you run), but I've done some tests on typical photographs (years ago). The histogram of the difference bitmap looks like this: 70% 0 10% +-1 5% +-2 2% +-3 1% +-4 .... Doing a huffman or lzw compression to data with such a histogram results in very good compression rates. And it's independent from the shape of the changes (a bounding rectangle or tiling probably saves some more percent). Well, for high contrast things like text on solid background, probably xor is as good (or using a completely different approach), because pixels often change completely. But modern GUIs are using color gradients or bitmaps with similar colors. If the user moves such a window slowly, many colors change smoothly, and in this case you get a histogram like the one above. Jens -- Jens Gruschel http://www.pegtop.net Back to top Jens Gruschel Guest Posted: Thu Feb 09, 2006 2:03 pm    Post subject: Re: Re-combining two bitmaps from delta image Quote: ok i und your point about the difference bitmap and compression, but i wonder how much the compression is better or worse than my maybe simple but straightforward approuch.. I haven't tried it, so of course what I said is pure speculation. But I guess the difference bitmap compresses much better when playing a movie on the screen or working with Photoshop, while it doesn't when working with Delphi or Word. Jens -- Jens Gruschel http://www.pegtop.net Back to top Francesco Savastano Guest Posted: Thu Feb 09, 2006 2:03 pm    Post subject: Re: Re-combining two bitmaps from delta image ok i und your point about the difference bitmap and compression, but i wonder how much the compression is better or worse than my maybe simple but straightforward approuch.. -- New World Software Creative Tools for Creative People http://new-world-software.com "Jens Gruschel" <nospam (AT) thisurldoesnotexist (DOT) com> ha scritto nel messaggio news:43e92378$1 (AT) newsgroups (DOT) borland.com... Quote: anyway it's never good to hit the limits.. Why not? As I already mentioned I don't see why he needs to do the difference of 2 bitmaps If he has the difference, he can use a better compression. Well, I don't know about typical screen images (probably it depends on what applications you run), but I've done some tests on typical photographs (years ago). The histogram of the difference bitmap looks like this: 70% 0 10% +-1 5% +-2 2% +-3 1% +-4 ... Doing a huffman or lzw compression to data with such a histogram results in very good compression rates. And it's independent from the shape of the changes (a bounding rectangle or tiling probably saves some more percent). Well, for high contrast things like text on solid background, probably xor is as good (or using a completely different approach), because pixels often change completely. But modern GUIs are using color gradients or bitmaps with similar colors. If the user moves such a window slowly, many colors change smoothly, and in this case you get a histogram like the one above. 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