Aspect keeping resize in convert_imageset

[ducha-aiki]

Three changes:

1. Added aspect keeping resize possibility to convert_imageset and io.cpp (as lots of people use it since "Some Improvements on Deep Convolutional Neural Network Based Image Classification" http://arxiv.org/abs/1312.5402 )
2. At<>`s changed to pointers for speed.
3. Function MatToDatum.

[sguada]

@ducha-aiki see #1070

[ducha-aiki]

@sguada nice PR! But it doesn`t cover aspect keeping resiz, so I will remove already merged stuff from my PR and make new one.

[sguada]

I think when people maintain the aspect ratio they don't resize it to make it square with black padding. I think it is more common to resize such that the minimum size is a fix number, i.e. 256, and the other dimension is resized appropriately to keep the aspect ratio.
I'm working in another PR to store the image files directly into the backend DB which will allow you to do any desired cv::Mat transformation afterwards.

[sguada]

@ducha-aiki see #1239

[ducha-aiki]

I have experimented with different setups and found that black padding often works best. Of course, depending on type of data you use.

-----Початкове повідомлення-----
Від: "Sergio Guadarrama" notifications@github.com
Надіслано: ‎08.‎10.‎2014 3:42
Кому: "BVLC/caffe" caffe@noreply.github.com
Копія: "Dmytro Mishkin" ducha.aiki@gmail.com
Тема: Re: [caffe] Aspect keeping resize in convert_imageset (#1178)

I think when people maintain the aspect ratio they don't resize it to make it square with black padding. I think it is more common to resize such that the minimum size is a fix number, i.e. 256, and the other dimension is resized appropriately to keep the aspect ratio.
I'm working in another PR to store the image files directly into the backend DB which will allow you to do any desired cv::Mat transformation afterwards.
—
Reply to this email directly or view it on GitHub.

[netheril96]

I think when people maintain the aspect ratio they don't resize it to make it square with black padding. I think it is more common to resize such that the minimum size is a fix number, i.e. 256, and the other dimension is resized appropriately to keep the aspect ratio.

@sguada That is how I do it. Is a square with black padding "aspect preserving" somehow?

[netheril96]

Besides, the padding should be a choice. An image will white background needs white padding, more complex images may need reflection or repetition based padding.

[ducha-aiki]

Replaced with #1550