Thumbnail is not the exact reduced copy of Image
Added by Paul Mybofy about 6 years ago
Bonjour
I extract a buffer containing a JPEG image from a postgresql database :
binarystring binStr(cursor0[1]); // from pqxx
const unsigned char *buffer = (unsigned char *)binStr.get();
Exiv2::Image::AutoPtr image = Exiv2::ImageFactory::open((Exiv2::byte *)buffer, binStr.length());
I can write image to a file :
Exiv2::FileIo file0("/Users/.../Tmp/toto.jpeg");
int sts = file0.open("w");
file0.write(image->io());
That is OK !
I extract the thumbnail from image :
image->readMetadata();
Exiv2::ExifData &exifData = image->exifData();
if (exifData.empty()) { cout << "exifData.empty()" << endl; }
Exiv2::ExifThumb *thumbnail = new Exiv2::ExifThumb(exifData);
I can write thumbnail to a file:
thumbnail->writeFile("/Users/.../Tmp/toto"); // OK !!! .jpg ajouté automatiquement
That is almost OK...
There is black bands at the top and bottom of the thumbail image.
The same appends when I write the thumbail to memory buffer and show the image on the screen...
I suppose there is a problem of size(height) of thumbnail vs size(height) of image, but I do not see how to proced to correct the problem.
Thanks for the help.
Sorry for my English.
Replies (2)
RE: Thumbnail is not the exact reduced copy of Image - Added by Robin Mills about 6 years ago
Your English is fine. I recently discussed reading and writing previews with Mike Ericsson: http://dev.exiv2.org/boards/3/topics/2250
I think this has something to do with the aspect ratio of your image and preview being different. Here's a photo I took at Stonehenge in July. My Nikon D5300 takes images at 6000x4000 (3/2) and the Preview is 160x120 (4/3). The preview has horizontal bars.
547 rmills@rmillsmbp:~/gnu/exiv2/trunk $ exiv2 -pa --grep Dimension http://dev.exiv2.org/attachments/download/805/DSC_7154.jpg Exif.Photo.PixelXDimension Short 1 6000 Exif.Photo.PixelYDimension Short 1 4000 548 rmills@rmillsmbp:~/gnu/exiv2/trunk $ exiv2 -pp http://dev.exiv2.org/attachments/download/805/DSC_7154.jpg Preview 1: image/jpeg, 160x120 pixels, 10837 bytes 549 rmills@rmillsmbp:~/gnu/exiv2/trunk $ exiv2 -ep --force http://dev.exiv2.org/attachments/download/805/DSC_7154.jpg 550 rmills@rmillsmbp:~/gnu/exiv2/trunk $ exiv2 DSC_7154-preview1.jpg 2>/dev/null File name : DSC_7154-preview1.jpg File size : 10837 Bytes MIME type : image/jpeg Image size : 160 x 120 551 rmills@rmillsmbp:~/gnu/exiv2/trunk $It looks as though my Nikon scales the image from 6000x4000 (3/2) to 160x106 (3/2). Then he add 2 'bars' of 7 black pixels to achieve a preview 160x120 (4/3). Perhaps the Exif standard requires the preview to be 4/3. I can't see this defined, however the example is 80x60. http://www.cipa.jp/std/documents/e/DC-008-2012_E.pdf
[Résolu] RE: Thumbnail is not the exact reduced copy of Image - Added by Paul Mybofy about 6 years ago
"It looks as though my Nikon scales the image from 6000x4000 (3/2) to 160x106 (3/2). Then he add 2 'bars' of 7 black pixels to achieve a preview 160x120 (4/3). Perhaps the Exif standard requires the preview to be 4/3. I can't see this defined, however the example is 80x60. http://www.cipa.jp/std/documents/e/DC-008-2012_E.pdf"
The same for my Sony X100.
I use wxWidgets which has the class wxImage :
wxImage Size (const wxSize &size, const wxPoint &pos, int red=-1, int green=-1, int blue=-1) const
Returns a resized version of this image without scaling it by adding either a border with the given colour or cropping as necessary. More...
Doing :
wxImage sizedThumb = imgThumb.Size(wxSize(160, 106), wxPoint(0, -7));
works fine.
Grand merci pour l'aide.