Imager: How to remove the alpha channel?
Posted on 2013-01-16 01:55:51.886443-08 by bugmenot
I'm currently using ImageMagick's convert command to convert a png to a tiff and to remove the transparent background and replace it with white (this is needed by tesseract ocr):
convert img.png -background white -alpha off -alpha remove
I haven't been able to figure out how to remove the alpha channel with Imager. So far all I have is
$image->write(file => 'output.tiff', i_background => '#ffffff')
but because tiff supports transparent backgrounds apparently, the i_background doesn't have an effect. how do i remove the alpha channel while making the background white?
Posted on 2013-01-16 03:56:25.050922-08 by tonyc in response to 13860
Create a new image, fill it with white and use rubthrough to compose the original over the background:
# source in $image my $back = Imager->new(xsize => $image->getwidth, ysize => $image->getheight); $back->box(filled => 1, color => "#FFFFFF"); $back->rubthrough(src => $image); $back->write(file => "output.tiff");
Posted on 2013-01-18 14:45:20.266128-08 by bugmenot in response to 13861
Thank you, that works great. I did notice, though, that the resulting TIFF produced by Imager is 3x the size of that produced by convert.
Posted on 2013-01-18 15:27:44.373874-08 by tonyc in response to 13867
If the input image is greyscale with alpha you can make the output image greyscale instead:
my $back = Imager->new(xsize => $image->getwidth, ysize => $image->getheight, channels => $image->getchannels() > 2 ? 3 : 1);
Assuming your fill colour is monochrome. Also, size will depend on what compression options you use, Imager defaults to packbits compression for TIFF, you can override that with tiff_compression => "lzw" for example.
Posted on 2013-01-18 22:45:10.804898-08 by hansey in response to 13868
How to cut video frame by frame and keep the key frames only on Mac MTS recordings from AVCHD camcorder are often highly compressed before stored, such a compressed movie contains key frames and non-key frames. Key frames can be displayed independently, while non-key frames can not be displayed without key frames. So such a functionality to locate and display every frame correctly, no matter key frame or non-key frame, is called frame accuracy (frame by frame). (Tip: Frame is one of the many single photographic images in a video.)
(This article is based on a thread on the CPAN::Forum.)