LibRaw technical support

Stable LibRaw versions: technical support, errors, API questions

How do I direct dcraw_emu to standard out for writing a jpeg on the fly....?

Submitted by robeastham on

When using dcraw I could set -c option to direct to stdout as specified at the top of the man page here:

https://www.cybercom.net/~dcoffin/dcraw/dcraw.1.html

This allowed me to write jpegs or pngs on the fly via the comand line (e.g. something like this: http://www.mutaku.com/wp/index.php/2011/02/cook-your-raw-photos-into-jpe...)

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Some questions to better understand the available data when opening a raw file with libraw

Submitted by irieger on

Hey folks,

last semester I did a nice seminar about image processing and somehow the demosaicing algorithms got me. So I'm now experimenting with different demosaicing and image processing algorithms and recently started to implement some testcode using libraw for reading DSLR photos. Now I have a few questions to better understand what's happening where the documentation didn't help or maybe I didn't understood it well.

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Different _mul(s)

Submitted by Sylvain on

Hi.

In my understanding, pre_mul, user_mul and cam_mul were mutually exclusive:
if use_camera_wb=1, cam_mul was being used, if use_camera_wb=0, it was pre_mul, and if pre_mul was defined, then pre_mul was being used instead of the 2 others.

However I ran the following test, showing that it is not true:

open()
no_auto_bright = 1
[...]
dcraw_process()

In [...], I try to use "as shot" white balance, setting either user_mul, pre_mul or use_camera_wb=1.
I was expecting all 3 pictures to be identical... but they're all different!

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Using Unprocessed raw data for OpenCV

Submitted by bdaniel on

Hi everyone,

First of all thanks for that wonderful library !

I've some issues, passing Raw Datas to an OpenCV Mat.

At first i used dcraw, but there is too much processing for me, my output images is blurred and pinked (yeah my picture has too much red in it i don't know why). So i tried to change dcraw processing params, but it was worse.

So i'm trying to used the unprocessed data and to fill a cv::Mat with it ! I read a lot of topics in this forum, and tried a lot of fixes, but i couldn't manage to do what i needed.

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.rawdata.raw_image and .image after unpack()

Submitted by octopode on

Hello,

After reading and trying out Libraw for a few days, I am confused with the structure of imgdata and what unpack() does to it:

When calling unpack(), the documentation at http://www.libraw.org/docs/API-CXX-eng.html#unpack
says:

Unpacks the RAW files of the image, calculates the black level (not for all formats). The results are placed in imgdata.image.

Yet there is also imgdata.rawdata.raw_image which gives me access to the raw unprocessed image.

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user_flip and Sony raws

Submitted by Sylvain on

Hi.

If I understand the documentation of user_flip correctly, not setting it (keeping it's default value of -1) should "auto rotate" the image according to what the accelerometers of the camera have detected when the image was shot.

Are there any known issues with Sony's arw files? It does not seem to work, while xnView (which claims to use dcRaw) rotates the image...

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Changing parameters without reloading/unpack()

Submitted by Sylvain on

Hi.

I wonder if it is possible to first call:
open_file(...)
unpack()

And then to call several times dcraw_process() -after changing pre_mul for example- without calling recycle(), open_file(...) and unpack() again?

Would memcpying imgdata.image after unpack and back do the trick?

Thanks,

Sylvain.

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About clipping and dcraw_process() stretching to 65535

Submitted by Sylvain on

Hi.

You've already explained that clipping in raw data was difficult to detect (has different forms), and that clipping values may even depend on the color channel.

Imagine a theoretical picture, with, after pre_mul or cam_mul applied, has:
red clipping to 60000.
green clipping to 40000 (I consider g and g2 to have the same behavior).
blue not clipping, climbing up to 50000.

How does dcraw_process() -no_auto_bright=1- stretch this result to 65535?

I guess it can't stretch each channel independently, since this would mess the white balance.

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Determine raw file-type

Submitted by Fimagena on

Hi,

Apologies if I missed something but is there an API-function to determine the file-type of the raw-file opened (and unpacked) with LibRaw?

Specifically, I would like to know if the file represented by the unpacked C++ LibRaw-class is a DNG-file. I can obviously check the filename extension but I'm assuming LibRaw does some internal matching of file types. Is that exposed through the API somewhere?

Many thanks!

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