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Video Compression?
Well, this is a bit off topic, but I thought I'd just ask.
If one chooses to "grayscale" a video (remove the color info), can one then recompress the video a lot more while keeping the same video resolution detail (i.e., due to eliminating wasting storage of any color information in the compressed file)? I guess one could ask the same question regarding storing images, too. IOW, could one convert a 1 MB color JPEG to perhaps 250 KB, and yet retain the same detailing (minus the color) |
#2
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Video Compression?
Bill in Co wrote:
Well, this is a bit off topic, but I thought I'd just ask. If one chooses to "grayscale" a video (remove the color info), can one then recompress the video a lot more while keeping the same video resolution detail (i.e., due to eliminating wasting storage of any color information in the compressed file)? I guess one could ask the same question regarding storing images, too. IOW, could one convert a 1 MB color JPEG to perhaps 250 KB, and yet retain the same detailing (minus the color) I tried it. 1) Windows Movie Maker 2) Drop my favorite test clip (~30 minutes) into timeline. 3) Save output as MovieRGB in "High Quality Video (Large)" format. 4) Go back to timeline. Click on the clip. Select special effects and apply Grayscale. 5) Save output as MovieGray in "High Quality Video (Large)" format. Results. Moviergb.wmv 56,671,234 bytes Moviegray.wmv 50,380,744 bytes So not a huge saving. A small savings possible. Codec info - Video was Windows Media Video 9, Audio was Windows Media Audio 9.1 44KHz stereo ******* The lossy compression methods, work in the frequency domain. Reducing the color palette, doesn't necessarily change the frequency (sharpness) of the thing. Which is why perhaps there isn't that much savings. I'll leave the testing of the JPG compression, to you :-) You can see DCT mentioned in here, as part of the compression. I like this article, for the set of images versus quality setting, which is convenient if you ever need to know in advance, what kind of Q setting to use for a particular job. Q=10 and 46:1 compression, still looks pretty good. Q=1, not so much. You could test at a constant Q, try your gray and color images, and see what a diff it makes. http://en.wikipedia.org/wiki/Jpeg Paul |
#3
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Video Compression?
Paul wrote:
Bill in Co wrote: Well, this is a bit off topic, but I thought I'd just ask. If one chooses to "grayscale" a video (remove the color info), can one then recompress the video a lot more while keeping the same video resolution detail (i.e., due to eliminating wasting storage of any color information in the compressed file)? I guess one could ask the same question regarding storing images, too. IOW, could one convert a 1 MB color JPEG to perhaps 250 KB, and yet retain the same detailing (minus the color) I tried it. 1) Windows Movie Maker 2) Drop my favorite test clip (~30 minutes) into timeline. 3) Save output as MovieRGB in "High Quality Video (Large)" format. 4) Go back to timeline. Click on the clip. Select special effects and apply Grayscale. 5) Save output as MovieGray in "High Quality Video (Large)" format. Results. Moviergb.wmv 56,671,234 bytes Moviegray.wmv 50,380,744 bytes So not a huge saving. A small savings possible. Codec info - Video was Windows Media Video 9, Audio was Windows Media Audio 9.1 44KHz stereo ******* The lossy compression methods, work in the frequency domain. Reducing the color palette, doesn't necessarily change the frequency (sharpness) of the thing. Which is why perhaps there isn't that much savings. I'll leave the testing of the JPG compression, to you :-) You can see DCT mentioned in here, as part of the compression. I like this article, for the set of images versus quality setting, which is convenient if you ever need to know in advance, what kind of Q setting to use for a particular job. Q=10 and 46:1 compression, still looks pretty good. Q=1, not so much. You could test at a constant Q, try your gray and color images, and see what a diff it makes. http://en.wikipedia.org/wiki/Jpeg Paul Thanks for the test, Paul. Seems like not much reduction in filesize. I haven't tried it on a JPG yet. :-) I was just trying to reason it out ahead of time (if it would even be applicable), since I don't really understand the compression algorithms yet, and how and when and where they are applied. Although I did know that color info (whenever and wherever it is being encoded and compressed) is normally given reduced weighting due to the eye being less sensitive, there). |
#4
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Video Compression?
In message , Bill in Co
writes: Paul wrote: Bill in Co wrote: Well, this is a bit off topic, but I thought I'd just ask. If one chooses to "grayscale" a video (remove the color info), can one then recompress the video a lot more while keeping the same video resolution detail (i.e., due to eliminating wasting storage of any color information in the compressed file)? I guess one could ask the same question regarding storing images, too. IOW, could one convert a 1 MB color JPEG to perhaps 250 KB, and yet retain the same detailing (minus the color) I tried it. [] Moviergb.wmv 56,671,234 bytes Moviegray.wmv 50,380,744 bytes [] I suspect it may also be affected by the source of the colour information in the video. If it's from older source material, where the colour _difference_ signal has been bandwidth-limited (PAL, SECAM, NTSC, video tape recorders), then it may be different from a video that records the full RGB difference, as most modern material probably does. I _suspect_ the ones with the bandwidth-limited colour difference signal would give less reduction in size when greyscaled. I think still images even uncompressed - i. e. BMP or similar - use fewer bytes per pixel in greyscale. Colour ones often contain at least a byte for each of the RGB elements of a pixel, making 24 bits; greyscale images rarely benefit from more than 64K levels of grey (2 bytes), and often 256 levels (1 byte) is sufficient. It also depends a lot on the image type: if it has few colours/greylevels (things like cartoons and logos), GIF can beat JPEG (it certainly doesn't lose detail, i. e. is lossless). -- J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf "The great tragedy of science, the slaying of a beautiful theory by an ugly fact. - Thomas Henry Huxley |
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