On Saturday 07 June 2008 10:31:11 am Bob Friesenhahn wrote:
> On Sat, 7 Jun 2008, Kevin Gale wrote:
> > I need to composite several JPEG / TIFF digital camera pictures that
> > use different profiles (Adobe RGB, Camera RGB Profile etc..) into a
> > single bitmap. I would appreciate it if someone could help answer
> > the following questions:
> > 1. Should I just convert the images to a single profile such as sRGB?
>
> Does sRGB support all the colors you are interested in?
I would avoid sRGB since is has a very limited gamut that is actually smaller
then the gamuts of many modern printers. Your Camera RGB gamut could be
almost twice as big as sRGB. There is a CM professional who has written books
on the subject who sometime posts to this and other color related lists that
likes to say "Friends don't let friends use sRGB". I agree with him sRGB is
not a good color space to do anything other then final rendoring for the web.
>
> > 2. The composited picture will eventually be printed to a digital
> > press such as a Canon ImagePress C1 or an HP Indigo. Should I
> > include the sRGB profile in my output JPEG or should I just save the
> > image without a profile?
As to saving the image with the profile you will need to talk to whoever will
be doing the printing. They should be able to tell you how to prepare the
images for them. They may ask that these be converted to a specific color
space or that you leave the profile embedded in the image. For example, a
big box store here in the US, Costco, has the profiles for each stores printer
available on line so that you can convert the images before bringing them in
for printing. If your printing service does not know how to answer this
question then you need to find another printing service.
>
> In order to preserve as much of the original as possible in the final
> output, perhaps it makes sense to convert your images to a colorspace
> which is as close to what these devices support as possible prior to
> composition. This approach prioritizes the quality of the printed
> output and may reduce artifacts such as banding. Another alternative
> is to chose a larger colorspace which best represents the colors in
> your images so that there is minimum original color loss and then your
> composited image is in that colorspace (with attached profile). This
> second approach prioritizes the quality of the composited master image
> over the quality of the device-specific image.
>
> Best quality composition may have completely different requirements
> depending on the type of composition used. There are those
> (particularly those in the compositing business) who will express the
> opinion that composition should only be done in a linear-light space
> (gamma "correction" removed). Camera RAW images are usually in
> linear-light space since that is what the sensors detect whereas
> camera JPEG images are usually white-point adjusted and gamma encoded
> to minimize loss with 8 bit storage, and to be more similar to sRGB.
>
> Bob
> ======================================
> Bob Friesenhahn
> [EMAIL PROTECTED], http://www.simplesystems.org/users/bfriesen/
> GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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