dds to png conversion colors wrong

[videomike99]

Hi All.
I'm new to ImageMagick, and am trying to convert an existing .dds image to .png, (or anything else for that matter).
Here's my command string:
convert colorbars.dds -set colorspace ycbca -colorspace rgb newfile.png

The original image can be found here: http://www.video-impressions.com/images/colorbars.dds

All of my conversion attempts either come out purple-ish, or green-ish, so I'm guessing it's a channel thing, but I'm just not that familiar with the program yet.

Any help would be appreciated.
Thanks,

Mike

[dlemstra]

What is your operating system and your ImageMagick version? And what is wrong with the output? It does contain green-ish and purple-ish values. Can you post your output somewhere?

[videomike99]

Windows 7 64bit
ImageMagick -6.9.3-Q16
Input file: http: http://www.video-impressions.com/images/colorbars.dds
Output file: http://www.video-impressions.com/images/newfile.png
What file should look like: http://www.video-impressions.com/images/ColorBars.png

The output is purple-ish when opened in photoshop.

Thanks for your assistance!

[fmw42]

convert colorbars.dds -set colorspace ycbca -colorspace rgb newfile.png

Is ycbca a type? Should it not be YCbCr? Also you should be using -colorspace srgb (for current versions of IM).

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convert colorbars.dds -set colorspace ycbcr -colorspace srgb newfile.png

Nevertheless, the above does not convert to match your colorbars.png on IM 6.9.3.8 Q16 Mac OSX. So are you sure the input DDS is really colorspace YCbCr?

[videomike99]

Sorry...I had a typo.
Below is the command string:

convert colorbars.dds -set colorspace ycbcr -colorspace rgb newfile.png

I've also tried:

convert colorbars.dds -set colorspace ycbcra -colorspace rgb newfile.png

[videomike99]

I'm not sure what the original colorspace is, so I've tried just about every one, as well as omitting the value and going with the default as well.

[snibgo]

After the image has been read, the colorspace is similar to YCbCr, but in the order CbYCr so we need to swap the first two channels.

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convert colorbars.dds -separate -swap 0,1 -combine -set colorspace YCbCr -colorspace sRGB x2.png

The result is close to the required colour chart, but not exactly the same.

[videomike99]

That's great...now it just seems like a gamma issue maybe...

[snibgo]

Sadly, no, it isn't just a gamma issue. My result gives "gray" patches that have slightly different values in the three channels.

[fmw42]

After the image has been read, the colorspace is similar to YCbCr, but in the order CbYCr so we need to swap the first two channels.

snibgo, I am just curious. I do not know DDS image format, so I am curious how you knew the channels were swapped. Are the Cb and Cr channels much different from the Y channel in values? Or was it just a guess on the way the colors seemed swapped?

[snibgo]

I know nothing about DDS.

After a simple "convert in.dds out.tiff" conversion, I looked at the pixel values in the bars that should be varying lightnesses of gray, using an image editor with eyedropper. The first and last channels were around 50%, with the middle value varying. So the middle channel seemed to be luminance or Y. I tried all the Y?? colorspaces and YCbCr seemed the closest fit.

I don't know if IM's DDS reader does any colorspace conversion, or re-arrangement of channels. dds.c is quite complex.

[fmw42]

snibgo,

You said that you used

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convert colorbars.dds -separate -swap 0,1 -combine -set colorspace YCbCr -colorspace sRGB x2.png

and that did not quite work out. Had you tried swapping Cb and Cr along with moving Y to the middle channel, i.e.

Code: Select all

convert colorbars.dds -separate -swap 1,2 -combine -set colorspace YCbCr -colorspace sRGB x2.png

If so, was that better or worse?

[snibgo]

Of the possible arrangement of channels Y-Cb-Cr, the one that fits best is Cb-Y-Cr. All other arrangements are clearly worse.

@videomike99: What software created colorbars.dds, or where did you get it from?