From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from smtp1-g21.free.fr ([212.27.42.1]:44274 "EHLO smtp1-g21.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752401Ab2DXKdW convert rfc822-to-8bit (ORCPT ); Tue, 24 Apr 2012 06:33:22 -0400 Date: Tue, 24 Apr 2012 12:34:12 +0200 From: Jean-Francois Moine To: Hans de Goede Cc: linux-media@vger.kernel.org Subject: Re: [PATCH v2] tinyjpeg: Dynamic luminance quantization table for Pixart JPEG Message-ID: <20120424123412.3b63810d@tele> In-Reply-To: <4F95CACD.5010403@redhat.com> References: <20120412122017.0c808009@tele> <4F95CACD.5010403@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-media-owner@vger.kernel.org List-ID: On Mon, 23 Apr 2012 23:34:05 +0200 Hans de Goede wrote: > Thanks for your work on this! I've just spend almost 4 days wrestling > which the Pixart JPEG decompression code to try to better understand > these cams, and I have learned quite a bit and eventually came up > with a different approach. > > But your effort is appreciated! After spending so much time on this > myself, I can imagine that it took you quite some time to come up > with your solution. > > Attach is a 4 patch patchset which I plan to push to v4l-utils > tomorrow (after running some more tests in daylight). I'll also try > to do some kernel patches tomorrow to match... Hi Hans, I tried your patch, but I am not happy with the images I have (pac7302). You say that the marker cannot be in the range 0..31 (index 0..7), but I have never seen a value lower than 68 (index 17). This last marker value (68) is the default when the images have no big contrasts. With such images / blocks, the standard JPEG quantization table does not work well. It seems that, for this value, the table should be full of either 7 or 8 (8 gives a higher contrast). Here is the sequence which works better (around line 1420 of tinyjpeg.c): -------------8<-------------- /* And another special Pixart feature, the DC quantization factor is fixed! */ qt[0] = 7; // 8 gives a higher contrast // special case for 68 if (marker == 68) { for (i = 1; i < 64; i++) qt[i] = 7; // also works with 8 } else { for (i = 1; i < 64; i++) { j = (standard_quantization[0][i] * comp + 50) / 100; qt[i] = (j < 255) ? j : 255; } } build_quantization_table(priv->Q_tables[0], qt); -------------8<-------------- About the other marker values, it seems also that the quantization tables are not optimal: some blocks are either too much (small contrasted lines) or not enough (big pixels) decompressed. As you know, a finer adjustment would ask for a long test time, so, I think we can live with your code. Best regards. -- Ken ar c'hentañ | ** Breizh ha Linux atav! ** Jef | http://moinejf.free.fr/