Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261504AbVBWRSQ (ORCPT ); Wed, 23 Feb 2005 12:18:16 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261508AbVBWRR4 (ORCPT ); Wed, 23 Feb 2005 12:17:56 -0500 Received: from witte.sonytel.be ([80.88.33.193]:15775 "EHLO witte.sonytel.be") by vger.kernel.org with ESMTP id S261504AbVBWRQS (ORCPT ); Wed, 23 Feb 2005 12:16:18 -0500 Date: Wed, 23 Feb 2005 18:15:48 +0100 (CET) From: Geert Uytterhoeven To: Paulo Marques cc: Matt Mackall , Gene Heskett , Linux Kernel Development Subject: Re: OT: Why is usb data many times the cpu hog that firewire is? In-Reply-To: <421C8193.2050808@grupopie.com> Message-ID: References: <200502211216.35194.gene.heskett@verizon.net> <200502211325.55013.gene.heskett@verizon.net> <20050221182952.GF6722@wiggy.net> <200502211708.27211.gene.heskett@verizon.net> <20050222231000.GA3163@waste.org> <421C8193.2050808@grupopie.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1594 Lines: 37 On Wed, 23 Feb 2005, Paulo Marques wrote: > Matt Mackall wrote: > > [...] > > JPEG data is DCT of 8x8 pixel chunks. If you can get at that, you can > > compare the DC terms of each chunk with minimal decoding. Various > > thumbnailers do this for speed already. > > I really doubt that this would work. It seems to me that you can have very > different DC terms with very similar results. In other words, even a little > noise in the picture might produce very different DC terms. It will cause only a slight difference, noise is mainly visible in the high-frequence parts. > Instead of comparing the DC terms, you could compare just the luminance. You > would have to decompress just half the data for that and you wouldn't need to > make the YUV->RGB conversion. That would probably save a few cycles. And since you cannot do `exact' comparisons of the luminance due to noise, but have to do some averaging, you're back to the previous solution: Hence compare the DC terms of the luminance. They're the average luminance of the 8x8 chunks. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/