Re: NSReadPixel returning different colors
Re: NSReadPixel returning different colors
- Subject: Re: NSReadPixel returning different colors
- From: John Stiles <email@hidden>
- Date: Mon, 8 Jan 2007 10:33:57 -0800
Or you could use a lower-level Apple API to decompress the PNG, like
the Image Compression Manager in QuickTime. This will probably offer
finer-grained control.
file:///Developer/ADC Reference Library/documentation/QuickTime/
RM/CompressDecompress/ImageComprMgr/index.html
On Jan 8, 2007, at 8:26 AM, Shamyl Zakariya wrote:
You may have to go directly through libpng; that will give you
direct access. I -- grudgingly -- did it since I needed to get
image data from PNGs without Cocoa pre-multiplying the alpha
channel. If going through libPNG is too much of a PITA, and if your
color map is small, you might just use a simpler uncompressed
format like tiff, or raw, and write your own accessor.
email@hidden
In the same episode, the scientist suggests that the
debigulation can only be reversed by a rebigulator.
-- wikipedia
On Jan 8, 2007, at 10:44 AM, John Stiles wrote:
Does the PNG have any gamma information in it? I am pretty sure
that the OS changed at some point to honor the gamma; previously I
believe it was ignored. So you might want to remove any gamma info.
Richard Holliday wrote:
On Monday, January 08, 2007, at 10:07AM, "Andreas Mayer"
<email@hidden> wrote:
Am 08.01.2007 um 15:32 Uhr schrieb Richard Holliday:
The original pixel color in the PNG file is R:153 G:255 B:153.
On the 10.4 machine I get back R: 0.6 G: 1.0 B: 0.6
On the 10.2 machine I get back R: 0.53 G: 1.0 B 0.53
I understand this is being color adjusted by the system but I
just need the raw values with nothing adjusted in any way.
You mean on 10.2? Well, that might just be a bug.
The values reported from 10.4 are without any adjustment.
0.6*255 = 153
Correct, the 10.4 values are fine it's just from 10.2.8.
Also, I tried my own code which returns the RGB values via the
[NSBitmapImageRep bitmapData] member. This has exactly the same
problem which lead me to believe I'm missing something else. As
soon as the PNG becomes an NSImage the data gets translated some
how?
There must be a way to get the original data before OSX / Cocoa
"messes" with it.
Richard
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