Boost Users :
Subject: Re: [Boost-users] [GIL] rotated90cw_view - jpeg lossless rotation
From: Sebastian Redl (sebastian.redl_at_[hidden])
Date: 2009-12-06 11:13:00
Christian Henning wrote:
> 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:
>> 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
> I think libjpeg has a way of applying lossless transformations while
> reading it. Is that correct, or am I mistaken here?
JPEG lossless transformation is a trick performed on the compressed JPEG
data (IIUC, you basically shuffle the values in each block), and can
therefore not be achieved by using a generic image library that provides
a JPEG reader and writer. You need specialized functions that operate on
the compressed JPEG data.
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