slow auto-rotate images when downloading from camera

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slow auto-rotate images when downloading from camera

Tom Malfrere
Hello,


I have a Canon 550D camera which takes 18Mpixel images.

I noticed that when I download the image from my camera there is a huge
speed difference between photo's in landscape and photo in portrait.
A landscape take about 0,5s to download while a portrait photo takes about 3s.
300 images at 3s a piece is 900s.
That's a long wait while it would normally only take 150s...

The problem is that the images in portrait are auto-rotated based on the
EXIF info.
I have no problem with the rotation but it just takes to much time.

I had the following idea:
1) Thread 1 downloads all the image from the camera to the PC as fast as
possible.
2) Thread 2 checks the downloaded images on disk to see if they need to
be auto-rotated based on the EXIF info. This second thread spawns a worker
thread for every image that must be rotated. The worker thread does the
actual rotating. Maybe the number of simultaneous worker threads should
be limited.

I'm posting this message here to know what other people think about this,
so let me know and post a message back.


Tom

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Re: slow auto-rotate images when downloading from camera

Jean-Michel Pouré-4
On Tue, 2010-08-31 at 10:16 +0000, Tom Malfrere wrote:
> I'm posting this message here to know what other people think about
> this,
> so let me know and post a message back.

For info, I noticed that downloading the images from the stick rather
than from the camera was much faster. But I did not enquire further.
This can differ from a camera to another based on the USB interface. But
downloading using an USB2 stick reader is pretty fast.

Rotating the image can downgrade quality if the pixels are not square.

For raw images, Digikam rotates the preview and this suits me very well.
So I don't have to rotate the image and downgrade quality.

Kind regards,
Jean-Michel

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