Hi Philip, On 15 Jan 10 12:53 Philip Rhoades <p...@pricom.com.au> said: > What still doesn't make sense is that if the original file is JPG > and one simply opens it and then saves it as another JPG file with > 100% quality - you are saying that introduced artifacts are adding > about 150% to the file size? (681 KB to 1.618 MB)
The %age, isn't one of straight file size reduction, but relates to the areas of the image to be averaged. The the more you reduce the quality the more you increase the potential for larger areas to be averaged. A "busy" image will not suffer much averaging regardless of the compression requested, but one with large areas of broadly similar colour, sky, painted walls, car bodywork, etc will have progressively larger areas averaged the more you reduce quality and the file size will reduce accordingly. Some images, for example, where there is a load of tumbling water and spray will barely reduce in size t all even at higher compression levels as no part of the image has a large enough plain area to allow it to be averaged. > How could the compression algorithms be so different as to cause > this sort of result? - At worst I would have expected maybe a 10% > increase in size . . I think you are assuming the whole imaged is compressed equally, regardless of the level of detail and colour change from one pixel to the next. Only in images with large areas of similar colour will the fle size reduce much at higher compression levels. The control is more one of "reduce this if you can", rather than "reduce it whatever the consequenses". Greg Chapman http://www.gregtutor.plus.com Helping new users of KompoZer and The GIMP _______________________________________________ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
