Legacy ImageMagick Discussions Archive

Hi!
I would like to convert a large number of 16bits per channel RGB DPX files that are used for a motion picture to PNG 16bits per channel.
Using identify, the DPX appear to have these specs :

DPX/DM_DANS_LES_EAUX_PROFONDES06476.dpx DPX 1920x1080 1920x1080+0+0 16-bit RGB 12.45MB 0.000u 0:00.000

When I convert them to PNG using the following command :

convert DM_DANS_LES_EAUX_PROFONDES06476.dpx PNG64:DM_DANS_LES_EAUX_PROFONDES06476.png

The resulting file have the following specs :

DM_DANS_LES_EAUX_PROFONDES06476.png PNG 1920x1080 1920x1080+0+0 16-bit sRGB 6.589MB 0.000u 0:00.000

Thus, there has been a colospace change from RGB to sRGB.
I am concerned that I lost some color precision in the process, though I'm not at all specialist in this.
Is this the case and if yes, how can I force convert to keep the RGB colorspace?
I tried the "-set colorspace RGB" and "-colorspace RGB" options but still ended with a sRGB file.
Maybe PNG is sRGB only?
As a side note, these PNG files will only be used to create video files at best in YUV422 colorspace, so keeping the full colorspace may be unecessary anyway.

If you put a sample DPX somewhere like dropbox.com and paste the RL here, someone can take a look.

What version of IM are you using?

The imagemagick version is imagemagick-6.8.6_10-x86_64-1.
Here is a sample of the source DPX files :

https://www.dropbox.com/s/rg9scg6o6qhfj ... 2.dpx?dl=0

And here is the resulting PNG file using the above-provided command :

https://www.dropbox.com/s/na3ydfn2bx6xi ... 2.png?dl=0

Under IM v6.9.0-0 on Windows 8.1, the command...

Code: Select all

convert DM_DANS_LES_EAUX_PROFONDES08682.dpx d.png

... creates a PNG that "identify" reports as being sRGB. However, the file is marked as gamma=1, and the PNG has a gamma chunk=1, and no sRGB chunk.

So it looks to me that "identify" is confused, and is mis-reporting this PNG as sRGB.

Perhaps a developer can take a look.

How do you check for those? Using "-verbose" with identify?

BTW, thanks for the replies!

Yes.

Code: Select all

f:\web\im>%IM%identify -verbose d.png
Image: d.png
  Format: PNG (Portable Network Graphics)
  Mime type: image/png
  Class: DirectClass
  Geometry: 1920x1080+0+0
  Units: Undefined
  Type: TrueColor
  Endianess: Undefined
  Colorspace: sRGB    <=== BAD
  Depth: 16-bit
  Channel depth:
    red: 16-bit
    green: 16-bit
:
:
  Rendering intent: Perceptual
  Gamma: 1    <<=== GOOD
  Chromaticity:
    red primary: (0.64,0.33)
    green primary: (0.3,0.6)
:
:
    png:gAMA: gamma=1 (See Gamma, above)        <<=== GOOD
    png:IHDR.bit-depth-orig: 16
    png:IHDR.bit_depth: 16
    png:IHDR.color-type-orig: 2
    png:IHDR.color_type: 2 (Truecolor)
    png:IHDR.interlace_method: 0 (Not interlaced)
    png:IHDR.width,height: 1920, 1080
    png:text: 38 tEXt/zTXt/iTXt chunks were found

[No sRGB chunk: GOOD]

OK, thanks!

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