Re: [Boost-users] [GIL] rotated90cw_view - jpeg lossless rotation

Subject: Re: [Boost-users] [GIL] rotated90cw_view - jpeg lossless rotation
From: Christian Henning (chhenning_at_[hidden])
Date: 2009-12-06 11:05:27

Hi Jose, please see comments below.

On Sun, Dec 6, 2009 at 5:10 AM, Jose <jmalv04_at_[hidden]> wrote:
> I rotate jpeg photos to portrait by reading the file and saving it like this:
>
>  boost::gil::jpeg_write_view(file,
> boost::gil::rotated90cw_view(boost::gil::view(img)));
>
> results:
>
> original size: 4106172 image/jpeg 3264 2448
> rotated size: 5594681 image/jpeg 2448 3264
>
> The rotation should be lossless (as the image is a multiple of the
> jpeg MCU) but the size has increased significantly and the exif tags
> disappeared.

I think libjpeg has a way of applying lossless transformations while
reading it. Is that correct, or am I mistaken here?

How do you preserve the exif tags? Does a user has to read them
separately and cache them?

In the new io extension there is the image_write_info structure which
would allow a user to pass additional information when writing images.
I would be more then willing to add functionality to the new gil::io.
Can you provide a small libjpeg example? I'll also have a look at
jpegtran.

>
> My questions:
>
> Has it been tested that the rotation is lossless ?
> What can I do make sure the exif tags are preserved ?

Good questions ;-) I'll investigate.

>
> thanks
> jose
>
Christian

PS: I see there is still one email from you I need to answer. Will do
that later on.