Keith Cooper wrote: > The benefits -may- come when you start manipulating the file. I've not > tried > it, but it might reduce posterisation or some other artefacts that can > appear for example if you push curves too far. Has anyone quantified > the > differences?
Keith, this is a tired old thread on another list - but the info gained so far is worthy of note, these edited archives are full of gold. http://www.ledet.com/margulis/ACT_postings/ACT-8-bit-16-bit.html (1999 thread archive) http://www.ledet.com/margulis/ACT_postings/ColorCorrection/ACT-16-bit-2002.htm (2002 thread archive) David Riecks writes: >> While working in 16 bit will provide "smoother" transitions between tonal areas, the real difference you are seeing is due to a wee bit of dithering that is added when you make the trip from 16 bit to 8 bit. << I tend to agree with David here. For a single channel job, some operations do have some benefit when working in higher bits (such as large g/blurs to a layer mask). I also agree on the dither comment. For 8bpc > 8bpc colour transforms in v6 or higher, the default colour setting behaviour is for a smart dither to be applied to tonal transition areas (this can affect file size to some small degree). It probably does not hurt, but I prefer to decide on a case by case basis using the convert to profile command if dither is applied to a colour transform. Most often dither is on, but not perhaps for a 'flat' rasterized layout image which is not a photo or gradation (no dither should be applied anyway, but I like to play things safe) or for web graphics where file size really matters). When editing in high bit mode and converting down to 8bpc, there is no option, the dither is applied. This is probably a good thing for non CG images or for those who do not have to factor in the addition of the dithered noise in the data (scientists and those not in graphic arts). For full colour/tonal images - the interaction of the three or four channels in RGB or CMYK tends to cancel out problems which are more apparent when working a single channel. If one wants to, one can get away with more data loss without the visual problems associated with monotone work. I can't recall thinking "if only I had worked in high bit mode..." - but it may happen one day. One should keep in mind that a histogram is only a statistical report on the pixels in an image - and as with any statistic one should take care with the conclusions one draws from it. The addition of dithered noise will affect the histo, revealing a 'better' histo...better depends on your viewpoint of how you interpret the data...for those in image editing for graphic repro the smoother histo provided by the high bit edits and the dither can seem appealing. I understand that a histogram can be very useful on the capture side of things with digital, but I personally have very little use for them in image editing for the purpose of evaluating the 'success' of an edit or the how useful an image is, although they have their place (the info palette and my eyes, experience serves this purpose). This is not an negative comment on those who do find histo's useful, this is just my perspective. It is fairly easy to make a histogram look better (if that is the goal) when the actual edits done to the image are more destructive to the content than the final histo may indicate. My viewpoint is that if you can afford the time/memory/storage overheads (temporary or permanent) of using high bit files - then why not (even more so with CS)?! At the same time, it is rare for me to use high bit files in the work that I generally do (art/prepress) and 8bpc is more than enough for me with the hardware that I use and the time and budget presented to me. And to answer the original post which is noted in the subject title... Not that I know of Jonathan, Photoshop 'honours' the bit depth presented to it...well for 8 bpc images that is (15bpc + 1b vs. 16 bpc or opening true 'high bit' files is another story which is more for those not in common graphic arts settings to worry over and to perhaps use other image editing software than Photoshop for some tasks). One could use an action/batch/droplet which as the first step after opening converts from regular bpc to high bpc and then use that way to work...and or assign an F key action to this command for use with open images. I am not sure on what possibilities scripting provides for this task. Sincerely, Stephen Marsh. =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
