On May 16, 2005, at 1:31 PM, Andrew Kimpton wrote:
On May 12, 2005, at 11:04 AM, Haroon Sheikh wrote:
Brendan does a good job describing the issue.
DeviceRGB, CMYK, & Gray color spaces are deprecated. You should
always use GenericRGB, etc. instead. GenericRGB represents an
ideal 1.8 gamma Mac color space that all monitors strive to
achieve. Think of it similar to sRGB but different gamma.
Are there performance impacts between the various colorspaces ?
For example we've been using (old code - I plan to update it)
DeviceRGB, recently our marketing people noticed that some of our
UI doesn't match the photoshop produced art they're used to seeing
and I determined that the photoshop art was was using sRGB. I made
the minor change to tweak our code to use the alternative
colorspace but saw such a dramatic performance loss i backed my
changes out again (at least for now 8-)
Any thoughts/suggestions ?
Andrew 8-)
This part I think I understand. :-)
If your code is reading in images, and those images are tagged as
sRGB, when the application draws the images to the screen, they will
have to go through a color management step. That color management
step takes some time.
Your best bet would be to read the images and perform the color
management on them once, then repeatedly draw the modified images.
There are several strategies you might take to do this.
If you need to support something "less than" 10.3, you can create a
bitmap context on your own memory and set that context's color space
to either the generic space or (even better) the color space of the
monitor. Then you can draw your image into that bitmap context and
the system will run it through the color matching. You create a new
CGImage from the results of that drawing (and dispose of the bitmap
context). What you are left with is a representation of your image
in a color space that will require little or no color matching.
If you support 10.3 and above, you can probably get away with using
CGImageCreateCopyWithColorSpace. As you read in each image, create a
copy and change the color space to the generic RGB space, or the
color space of your monitor.
If you are working on 10.4, then you might find some advantage to
drawing your UI elements into a CGLayer. A CGLayer is something like
a mutable offscreen image when you are planning to draw that image
repeatedly to the same context. When you create a CGLayer you
associate it with the context that you will eventually be drawing
on. Then, as you add things to the layer, the computer can optimize
the repeated drawing of that layer to the destination context. That
means, for example, that the CGLayer might choose to do the color
matching up front once. If you can be Tiger only, I would at least
consider trying CGLayer and see if it restores your performance.
Or you could talk your UI designers into using a color space other
than sRGB :-)
Scott
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