Questions and postings pertaining to the development of ImageMagick, feature enhancements, and ImageMagick internals. ImageMagick source code and algorithms are discussed here. Usage questions which are too arcane for the normal user list should also be posted here.
Why do you do resizing twice, once with -thumbnail and then again with -resize. Seems to me that you can do it just once.
PNG images are always sRGB, so using -colorspace sRGB is redundant.
specifying -scene 1 only affect the output number assigned if you had more than one frame or layer. Since you have use layer [0], there is no need for -scene 1
Imagemagick 7 by default installs as HDRI, which will be slower than without HDRI. Be sure you have compile your IM 7 and IM 6 with the same features and whether you have OpenMP or not the same and the same number of threads in use. Check your
Are the Q-numbers the same? HDRI? Are the libraries the same? Did you run both tests twice, taking just the final readings? On tests like this, my computer is always much faster after the first run. I suppose the files are cached somewhere.
I would expect v7 to be slightly slower than v6 at most operations on colour images, because of the way pixel channels are accessed.
I notice the input JPG also, but forgot to mention that. JPG has not layers and does not support transparency. Though it can support CMYK. So the colorspace would be needed, but there is no need for -background ... -flatten, nor the double resizing, nor the [0], nor the -scene 1.
When you run tests, you probably should start with the simplest command and work up with more settings and methods incrementally to see where it is slowing down. Perhaps just a simple convert from PNG to JPG would suffice to see the timings.
But I suspect that much has to do with different IM compile features. Though snibgo may be correct with regard to the way IM 7 handles channels different from IM 6.
I agree with your comments, Fred. I haven't done timing tests on v6 versus v7. If I did, I would use the current versions of both, ensuring the libraries, Q-number, HDRI, OpenMP etc were identical.
I would expect v7 operations to be slightly slower than v6 for colour images, but much faster for grayscale. But I haven't tested this.
Thanks all, this has been indeed helpful. I was experimenting with ImageMagick convert pdf to jpg thumbnails. For this reason I had the first page only selected as scene 1. My requirement is to have 3 thumbnail sizes, 720x480 is one of them so added the resize option.
I verified the versions In my analysis I was doing a comparison of ImageMagick-6.8.5-7c and ImageMagick-7.0.2-7.The comparisonwas done against jpg to jpg and png to jpg. Accidentally I pasted the jpg-jpg call. Sorry for that. Here is the comparison snapshot for both the runs
for both systems. We would like to see that you are comparing apples to apples. You might also try compiling IM 7 without HDRI so you have both systems the same.
It would be a better test if you just did timings on
