<PhotoRoy6@xxxxxxx> asks: : Does the new Jpeg XR (Microsoft HD) format loss info every time the file is : save like the current jpeg? : Does the current jpg format at 12, minimum compression loose info ? re Jpeg XR : "Full decoding is also unnecessary for certain operations such as cropping, downsampling, horizontal or vertical flips, or cardinal rotations. All color representations are transformed to an internal color representation. The transformation is entirely reversible, so, by using appropriate quantizers, both lossy and lossless compression can be achieved." That is to say you can have either a lossy JpegXR or a truly lossless one - it's up to the user when they use and save in this container.. which is TIF based. And as to whether a jpeg loses info every time it's saved - well that need not be the case. Even rotating a jpeg is described as a lossy procedure, cropping it, basically doing anything to it, but that also need not be the case as it very much depend on the program that is used to handle these operations. Imagine if your mechanic didn't have the tools to balance the tyres on your car, it'd be silly to say the wobbly ride was as a result of the tyres being rubbish. Apparently the Very Professional Photoshop® behaves in such a manner as our mechanic in question - it hasn't the tools to handle a jpeg losslessly and thus the jpeg is blamed for its poor performance. In fact there are many programs available which can handle a number of totally lossless transformations - totally losslessly ;) The JpegXR is a different animal though, and will probably become very popular with Photoshop® users given that Adobe® will be supporting it fully as a co-developer. : Does the current jpg format at 12, minimum compression loose info ? In Abobe products? yes. If what you mean is in converting an image from another format to a jpeg, that's a yes too. However what is 'lost' is often information that was in excess of what could be realistically 'used' anyway for anything other than further editing. An analogy to that would be shooting a B&W neg at 3-4 stops over the speed rating and applying a reduced development time to get a massive long sweeping contrast curve. Yes you have a HUGE tonal range, but when you print it you; A. still end up printing only a fraction of the full range on the neg and; B. you end up with a muddy, low contrast image. Better to shoot as close a contrast and as close a tonal range to what you want for the final print right at the get go. In saying that, I'm neglecting your working material though. A jpeg isn't the ideal tool for image manipulation by any means! If you were to start with a jpeg the best bet is to convert it to a BMP before any editing. Add, subtract, manipulate, fiddle, twiddle and maul and when the image is finished, save the final as a jpeg (with loss of course). If you're starting with another format, same deal, work with the maximum amount of info during the manipulation stage. Every image container has its problems though, GIF is lossless and utter rubbish for 90% of photographs. PNG is lossless too, but not as widely used as it could/should be - BMP's are lossless but huge. (not really part of the discussion but TIF images can and have been used to cause buffer overflows and run hostile code. Even maliciously coded RAW images have been found to exploit security vulnerabilities on Apple Mac OSX systems - nothing's perfect!). Jpegs other oft quoted limitation is its 8 bit colour depth. While this may be a limiting factor in editing images, it's generally not a limit to printing them (all inkjet printers are 8 bit) nor to viewing them on 90% of computer set-ups- the only monitor set-up that can display images with more than colour depth than 8 bit is a CRT fed by a Matrox graphics card (10 bit), but they are becoming less common as folks adopt game playing graphics cards and LCD's. karl
