BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  StretchBlt quality.          BorlandTalk.com Forum Index -> C++ Builder (Graphics) View previous topic :: View next topic   Author Message Lars Guest Posted: Sun Jan 11, 2004 8:34 pm    Post subject: StretchBlt quality. Hi, I use the windows API StretchBlt to resize my images, since it does a far better job with the HALFTONE attribute opposed to StretchDraw. However, it's quality is close, but not as good as, a resized image in Photoshop. I would like to know if anyone knows how Photoshop does the resizing, or if there is any other approaches to resizing an image to produce maximum quality for BCB 6.0. Thanks Back to top Dennis Jones Guest Posted: Mon Jan 12, 2004 4:11 am    Post subject: Re: StretchBlt quality. "Lars" <Lars (AT) MagikaStudios (DOT) com> wrote Quote: Hi, I use the windows API StretchBlt to resize my images, since it does a far better job with the HALFTONE attribute opposed to StretchDraw. However, it's quality is close, but not as good as, a resized image in Photoshop. I would like to know if anyone knows how Photoshop does the resizing, or if there is any other approaches to resizing an image to produce maximum quality for BCB 6.0. That's interesting, because StretchDraw uses StretchBlt internally. I don't know if this will help you or not, but I wanted a better result from StretchDraw/StretchBlt some time ago, and after doing a little bit of research (I'm no graphics expert) found out the following: StretchBlt uses a "nearest neighbor" algorithm when stretching an image, and usually results in reasonably good image quality. CopyImage, on the other hand, uses a "bilinear interpolation" algorithm, and usually results in a smoother (subjectively speaking) stretched image than StretchBlt. There is one caveat that I discovered while using CopyImage: it requires that the image have a 24-bit pixel depth for the interpolation algorithm to work. It might worth a look. - Dennis Back to top Mauro Guest Posted: Fri Jan 16, 2004 3:49 pm    Post subject: Re: StretchBlt quality. Lrs, give me an example with a bitmap (windows API StretchBlt ) that you copy from image1 to image2 from size 80x80 to 40x40. Thanks Mauro "Dennis Jones" <djones (AT) nospam (DOT) com> schrieb im Newsbeitrag news:40021e55$1 (AT) newsgroups (DOT) borland.com... Quote: "Lars" <Lars (AT) MagikaStudios (DOT) com> wrote in message news:4001b3d6 (AT) newsgroups (DOT) borland.com... Hi, I use the windows API StretchBlt to resize my images, since it does a far better job with the HALFTONE attribute opposed to StretchDraw. However, it's quality is close, but not as good as, a resized image in Photoshop. I would like to know if anyone knows how Photoshop does the resizing, or if there is any other approaches to resizing an image to produce maximum quality for BCB 6.0. That's interesting, because StretchDraw uses StretchBlt internally. I don't know if this will help you or not, but I wanted a better result from StretchDraw/StretchBlt some time ago, and after doing a little bit of research (I'm no graphics expert) found out the following: StretchBlt uses a "nearest neighbor" algorithm when stretching an image, and usually results in reasonably good image quality. CopyImage, on the other hand, uses a "bilinear interpolation" algorithm, and usually results in a smoother (subjectively speaking) stretched image than StretchBlt. There is one caveat that I discovered while using CopyImage: it requires that the image have a 24-bit pixel depth for the interpolation algorithm to work. It might worth a look. - Dennis Back to top Winter Guest Posted: Fri Jan 16, 2004 4:30 pm    Post subject: Re: StretchBlt quality. SetStretchBltMode(Image1->Picture->Bitmap->Canvas->Handle,HALFTONE); StretchBlt(Image2->Picture->Bitmap->Canvas->Handle,0,0,40,40,Image1->Picture ->Bitmap->Canvas->Handle,0,0,Image1->Picture->Bitmap->Width,Image1->Picture- Quote: Bitmap->Height,SRCCOPY); The key here is to set the HALFTONE first, this will make the image look alot better. Hope this helps. Lars Back to top Mauro Guest Posted: Mon Jan 19, 2004 6:37 am    Post subject: Re: StretchBlt quality. Thanks Lars, it is better, but have a look on the Damon's coding, the resized pictures look great! 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