Converting DPX to sRGB colorspace

[digobh]

Hi

I'd like to convert a dpx to a jpg but getting a result as close as nuke does.
I am using the command below. Close, but not the same colors though. Heaps of variations happening.

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convert -colorspace sRGB input_filename.dpx -set colorspace sRGB -level 0.74%,58%,0.74 -quality 100% output_filename.jpg

The -level option is to apply a SRGB look up into my jpg, as ImageMagick doesn't seem to do by default.
I am on Linux(ubuntu 12.01) and I've tried using -profile sRGB.icc but I get the error below:

convert: unable to open image `sRGB.icc': @ error/blob.c/OpenBlob/2587.
convert: unable to open file `sRGB.icc': @ error/blob.c/FileToBlob/925.

Using Only the command bellow, wihtout the -level option leaves my jpg with a different lookup. The jpg looks washed out.

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convert -colorspace sRGB input_filename.dpx -set colorspace sRGB -quality 100% output_filename.jpg

Does any one know ho to get he look up looking correct? I just want to get my jpeg from ImageMagick looking the same as my jpeg from nuke. In Nuke I load my file as Cineon(dpx) and Save as SRGB(jpg). And they look exacly the same.

thank you very much for your attention

Rodrigo Guimaraes

[digobh]

Hi folks,

I sort of found a solution to my problem baking a lut to the file. Now my conversion looks very much like Nuke.
This is using the Hald Clut from Imagemagick. I am not sure if this is the right approach, however, from all alternatives that I found through the forums, that's the best for me that matches nuke color lookups.

Creating a Hald File for color lookups.

For more info go to the source, under: Hald 3D Color Lookup Tables http://www.imagemagick.org/Usage/color_mods/
The command below will create a raw Hald File for you.

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convert   hald:8    hald_8.png

You would use at least a level 8 Hald (the default), which will hold a color cube with 256 colors per side, or 16777216 colors, and produce an image that is 512x512 pixels in size. Such a "hald:" image has every possible 24 bit color possible (3 channels at 8 bit color depth), and saves into an approximately 10Kbyte PNG image.

Now what I did was to bring the had_8.png to nuke, reading as cineon colorspace ans saving it as sRGB colorspace. Then I saved to hald_8_cineon_to_sRGB_nk.png. now this file contains the color difference from hald_8.png

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convert input_file.dpx hald_8_cineon_to_sRGB_nk.png -hald-clut output_file.jpg

The hald image above (hald_8_cineon_to_sRGB_nk.png) is the file hald_8.png read as Cineon and saved out as sRGB in nuke. That bakes out the colorspace change to the hald file.

[anthony]

The -level option is to apply a SRGB look up into my jpg, as ImageMagick doesn't seem to do by default.

Actually -level doesn't have anything to do with colorspace. Level modifies values as they currently exist.
Also -set colorspace does not modify the values, just change the colorspace setting without converting values.

As such the two have no effect on each other at all! On the other hand using -colorspace sRGB will convert the values and thus effect the results of -level.

[digobh]

Hi Anthony,

Thanks for the Clarification. I've noticed that with -set corlospace SRGB, I always got nothig.
Although, using -colorspace sRGB I always get an washed out Image. Maybe coz it's not applying a sRGB LUT on it?

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convert input.dpx -colorspace sRGB output.jpg

Cheers

Rodrigo Guimaraes

[fmw42]

what version of IM are you using. Before IM 6.7.6.7 -colorspace RGB was sRGB and -colorspace sRGB was RGB.
see
viewtopic.php?f=4&t=21269

[digobh]

Hi

I am using,

Version: ImageMagick 6.6.9-7 2012-04-30 Q16

I've tied the different command below based on the link you sent me:
It gives me a extremely washed out jpg.

convert input.dpx -colorspace rgb -colorspace sRGB output.jpg

Thanks for your attention

PS: My DPX is in Cineon Color Space, Log.

[fmw42]

Your version of IM was before the sRGB vs RGB switch. Thus you do not need to add -set colorspace RGB.

I do not know if you will ever get as close as Nuke.

PS: My DPX is in Cineon Color Space, Log.

That is why your -colorspace sRGB changes your image. But so will -colorspace RGB. You are converting from LOG colorspace, it would appear to either RGB (by -colorspace sRGB) or sRGB (by -colorspace RGB). To convert properly, you may have to use profiles. See if your image has a profile (icc or icm) by identify -verbose yourimage.dpx

I do not know if JPG supports LOG colorspace.

I think you will need to post a link to your file so that the IM developers and others can test with it.

How are you viewing your original and your converted files? Perhaps it is a viewer issue. Perhaps the viewer cannot handle LOG colorspace?

[anthony]

two -colorspace operations following each other just adds extra conversions for no gain (unless testing conversion round trips).

Note -colorspace it is not the -profile operator. I always thought -profile was silly in having both its set and convert in the same option! It should also give a warning if you try to convert and no profile is set in the image.

Sorry ranting.. back to the problem at hand.

As for the washed out look. I believe DPX should be using a 'LOG' colorspace by default. If it isn't then that may be a bug. I am not certain as I don't actually use it.

If it is a LOG colorspace and it was not set properly try this

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  convert input.dpx -set colorspace log -colorspace RGB output.png

That assumes the older version of IM otherwise use sRGB for newer versions.