hi. sorry for the late reply. i was on holiday....

Florian Walter wrote:

Hallo, I would like to do some video analysis to control the playback of audio files. pix_movement and pix_blob work quite well, but now I would like to go into details and have some questions:

• How can I apply a color filter to an image? I would like to distinguish the movement of different colors...

use [pix_rgb2hsv] to convert the image into HSV-colorspace (the actual colorspace is still GL_RGBA, but the "red" channel will be "hue",...) then use [pix_curve] to mask out the colors ("hue") that you don't want. finally use [pix_blob] only on the 1st channel ("hue").

i attach i (quite chaotic) patch that should show you the idea (it does NOT do motion-tracking but simple colortracking instead)

• Is there an object that returns the total brightness of an image? Or are there other possibilities to detect the "amount" of movment in a video?

the last outlet of [pix_blob] is the size of the blob, which is proportional to the amount of movement.

(I read about pix_mean_color in the archives but I can't find it in gem 0.90.1...)

there is an experimental binary for w32 available on the download site at http://gem.iem.at

for self-compiling check out the CVS.

• I would like to recognize whether big blocks of a single color or fine noise-like structures are moving. Downsamling might be a good solution to get away the fine structures and to reduce the number of pixels inside of a colored block that are not recognized as moving. pix_resize didn't change anything (are there any parameters I can pass to that object?) and needs lots of computing power... Any ideas how to solve this problem?

try to capture with the lowest feasible resolution in the first place.

[pix_resize 32 32] should resize your image to 32x32 pixels. [pix_movement] takes an optional arugment to set a threshold: if the movement in a pixel is smaller than the threshold, it is not taken into account. (but you still cannot detect, whether you have a number of small blobs or as single bigger one) with [pix_convolve] you can do lowpass-filtering of the image (and hopefully get rid of noise)

[pix_multiblob] (i doubt whether this is in the 0.90.1 release) is a bit more sophisticated, as it returns not only the size ("total brightness") of each individual blob but also the area covered by the blob

hope this helps.

mfga.sdr IOhannes

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