[Digikam-users] Re: Store image as AdobeRGB

[Gilles Caulier]

2010/12/2 Marcel Wiesweg <marcel.wiesweg at gmx.de>:
>
>> Hm, maybe you could tell me where I would have to look exactly for the
>> color profile? I did not try jpg or png yet.
>
> The right sidebar, Color / Profile is the right place. Any wrong information
> there is a bug.
>
>> I'm still looking for some
>> good master format to save my images during my editing workflow. Until now
>> I thought about jpg2000 or tiff. Any other recommanedations?
>
> There are four in the choice of lossless file formats: PNG, TIFF, JPEG2000,
> PGF.
> PNG and TIFF will result in pretty large files: TIFF is often not compressed
> at all,

This depend. TIFF is a general image container. by default it's not
compressed but LZW compression can be used. There is an option in
digiKam config panel.

TIFF can also use JPEG compression or other stuff... But it's not
implemented in digiKam...

http://en.wikipedia.org/wiki/Tagged_Image_File_Format#Flexible_options

 and PNG uses a simple compression scheme (you get  small files if
> there are large parts in the same color, like charts or diagrams, obviously
> not for real-life photos).

Adobe deflate compression is used in PNG. It's a little bit better
than TIFF in general (5%)

> Advantages of TIFF and PNG: widely supported - you
> can pass files around to your friends - and low computation when loading /
> saving (but when files are larger, harddisk access takes longer, I dont know
> if they really load and save faster)


> JPEG2000 and PGF are technically superior, modern file formats, based on
> Wavelet transformation. Both support lossy and lossless encoding. Lossy
> encoding will give better results than JPG, and lossless will give smaller
> files than PNG or TIFF. JPEG2000 is optimized for compression ratio, PGF is
> much faster,

because there is no float computation, only integer cast are used
inside. JPEG2000 is slow because all computation are based on float.

>giving only slightly larger files AFAIK. The only drawback of
> these formats is that they are not as widely supported as JPG, PNG or TIFF,
> PGF probably even less then JPEG2000.
>

JPEG 2000 is not used in photo. As PGF, it's Archiving format. In
digiKam, we have deeply supported these format to store all metadata.
This is not the case in others photo management program, or photo
editor.

JPEG2000 and PGF give same compression ratio.

Note : a challenger arrive in photo world : JPEGXR. It's the famous HD
photo format from M$ !!!

http://en.wikipedia.org/wiki/JPEG_XR

It's a TIFF based image format, using wavelets compression and using
integer encoding. It's exactly the same than PGF, excepted than PGF is
GPL, and JPEGXR is patented. It's Microsoft stuff of course.

JPEGXR have been normalized by JPEG consortium. The goal is to replace
JPEG as well in camera. Can you imagine the future problem ?

M$ provide a SDK which compile under Linux with few modification. JPEG
group as also implemented a library, not yet published (beta) with no
OpenSource compatible license of course.

Gilles Caulier