I've been going around in circles with this one
What is a good way to change the brightness and contrast in an NSImage?
I've been playing with the vImage library for changing contrast,
using the vImageEndsInContrastStretch. This works, but how does one
return the contrast to it's original value? you specify that
0% of the pixels lie at the histogram extreme, you can't get the
original values back. I know of the ImagApp example showing how to
use CIImage, but using that would require a re-write of quite a bit
of code I'd rather not go there.
I start with images that have maximum contrast to begin with (I get
digital data from a sensor, then create an NSImage by scaling the
pixel values from 0 -255). So when I stretch the contrast, a bunch
of pixels hit the rails those values are gone forever. Same thing
if I compress the contrast quantization destroys the original
information. How do people typically deal with this? Take iPhoto.
If I change the contrast, I can move the slider back to low contrast,
and all the data seems to be there do they just not allow any data
to hit the 0-255 rail, or is a temporary copy being stored? If I
keep increasing contrast, quitting, increasing contrast, quitting,
etc, I CAN destroy the information, and have to revert to original
therefore, I'd say that not allowing data to hit the rail is not the
answer.
Any discussion, up to and including sample code, would be greatly
appreciated.
Thanks,
Eric
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Dec 2, 2005, at 9:29 PM, Eric Smith wrote:

I've been going around in circles with this one

What is a good way to change the brightness and contrast in an
NSImage?

I've been playing with the vImage library for changing contrast,
using the vImageEndsInContrastStretch. This works, but how does
one return the contrast to it's original value? you specify
that 0% of the pixels lie at the histogram extreme, you can't get
the original values back. I know of the ImagApp example showing
how to use CIImage, but using that would require a re-write of
quite a bit of code I'd rather not go there.

Too bad, because that's how to do it.
-jcr

John C. Randolph <jcr (AT) mac (DOT) com(408) 914-0013
Roaming Cocoa Engineer,
Available for your projects at great Expense and Inconvenience.

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CIImage wasn't even around until 10.4 there must be a way to
handle this from an NSImage. Anyone out there use brightness and
contrast controls on an NSImage, or the bitmap data associated with
the NSImage?

Thanks,
Eric

Dec 2, 2005, at 9:34 PM, John C. Randolph wrote:

Dec 2, 2005, at 9:29 PM, Eric Smith wrote:
>
>I've been going around in circles with this one
>>
>What is a good way to change the brightness and contrast in an
>NSImage?
>>
>I've been playing with the vImage library for changing contrast,
>using the vImageEndsInContrastStretch. This works, but how does
>one return the contrast to it's original value? you specify
>that 0% of the pixels lie at the histogram extreme, you can't
>get the original values back. I know of the ImagApp example
>showing how to use CIImage, but using that would require a re-
>write of quite a bit of code I'd rather not go there.
>
Too bad, because that's how to do it.

-jcr
>
>
>
John C. Randolph <jcr (AT) mac (DOT) com(408) 914-0013
Roaming Cocoa Engineer,
Available for your projects at great Expense and Inconvenience.
>
>
>

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I would recommend using CoreImage for doing this. There are AppKit
categories on CIImage that are the same as NSImage API. There is also
NSCIImageRep, or rendering your CoreImage into an NSImage. Any or
some combination of these should allow you to slip CIImage into your
system without modifying the rest of your code.

In my application the difference between using NSImage and CIImage
boils down to about 10 lines of code. (After many gyrations - see
previous thread on CIImage performance)
-Kenny

Dec 3, 2005, at 7:04 PM, Eric Smith wrote:

CIImage wasn't even around until 10.4 there must be a way to
handle this from an NSImage. Anyone out there use brightness and
contrast controls on an NSImage, or the bitmap data associated with
the NSImage?

Thanks,
Eric

Dec 2, 2005, at 9:34 PM, John C. Randolph wrote:
>
>>
>Dec 2, 2005, at 9:29 PM, Eric Smith wrote:
>>
I've been going around in circles with this one

What is a good way to change the brightness and contrast in an
NSImage?

I've been playing with the vImage library for changing contrast,
using the vImageEndsInContrastStretch. This works, but how does
one return the contrast to it's original value? you specify
that 0% of the pixels lie at the histogram extreme, you can't
get the original values back. I know of the ImagApp example
showing how to use CIImage, but using that would require a re-
write of quite a bit of code I'd rather not go there.
>>
>Too bad, because that's how to do it.
>>
>-jcr
>>
>>
>>
>John C. Randolph <jcr (AT) mac (DOT) com(408) 914-0013
>Roaming Cocoa Engineer,
>Available for your projects at great Expense and Inconvenience.
>>
>>
>>
>

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I think the problem is it isn't clear what you are asking for

Are you asking for pointers to general brightness and contrast
algorithms?
Are you asking how to get at the NSImage bitmap data to manipulate it
yourself?
are you asking if there are other Apple supplied frameworks that
will perform brightness and contrast adjustments for you?

Dave

Dec 3, 2005, at 8:04 PM, Eric Smith wrote:

CIImage wasn't even around until 10.4 there must be a way to
handle this from an NSImage. Anyone out there use brightness and
contrast controls on an NSImage, or the bitmap data associated with
the NSImage?

Thanks,
Eric

Dec 2, 2005, at 9:34 PM, John C. Randolph wrote:
>
>>
>Dec 2, 2005, at 9:29 PM, Eric Smith wrote:
>>
I've been going around in circles with this one

What is a good way to change the brightness and contrast in an
NSImage?

I've been playing with the vImage library for changing contrast,
using the vImageEndsInContrastStretch. This works, but how does
one return the contrast to it's original value? you specify
that 0% of the pixels lie at the histogram extreme, you can't
get the original values back. I know of the ImagApp example
showing how to use CIImage, but using that would require a re-
write of quite a bit of code I'd rather not go there.
>>
>Too bad, because that's how to do it.
>>
>-jcr
>>
>>
>>
>John C. Randolph <jcr (AT) mac (DOT) com(408) 914-0013
>Roaming Cocoa Engineer,
>Available for your projects at great Expense and Inconvenience.
>>
>>
>>
>

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K. I have NSImages that I've created by filling an NSBitmapRep's
data buffer with information that I get from an image sensor. When I
create the rep, I scale all the data from the sensor so that I get a
grayscale image spanning 0-255 in each color channel so I start
with maximum contrast.

So, part one of the problem is, what's the most efficient way of
changing the brightness and contrast of this image? vImage uses
Altivec, and was my first choice for speed. vImage does have a
function for *increasing* the contrast works just fine. Problem
is, I start with maximum contrast, so any contrast stretching causes
information near the edges of the histogram to be lost ie,
everything from, say, 200 - 255 gets mapped to 255. Question: how
do people typically deal with this problem? Keep an original bitmap
around in case one wants to reduce the contrast (get back all the
original information) ?

Part two of the problem: vImage has no brightness control (unless
it's called something else, and I just don't recognize it that's
possible). Does it exist somewhere else? Question: does Apple
provide a set of routines that operate on either and NSImage, or the
bitmap rep, that will change the brightness and contrast for me?

I'd also be interested in general brightness and contrast algorithms,
if anyone has info they'd like to pass along.

Thanks,
Eric

Dec 3, 2005, at 7:30 PM, Dave Camp wrote:

I think the problem is it isn't clear what you are asking for

Are you asking for pointers to general brightness and contrast
algorithms?
Are you asking how to get at the NSImage bitmap data to manipulate
it yourself?
are you asking if there are other Apple supplied frameworks that
will perform brightness and contrast adjustments for you?

Dave

Dec 3, 2005, at 8:04 PM, Eric Smith wrote:
>
>CIImage wasn't even around until 10.4 there must be a way to
>handle this from an NSImage. Anyone out there use brightness and
>contrast controls on an NSImage, or the bitmap data associated
>with the NSImage?
>>
>Thanks,
>Eric
>>
>Dec 2, 2005, at 9:34 PM, John C. Randolph wrote:
>>

Dec 2, 2005, at 9:29 PM, Eric Smith wrote:

I've been going around in circles with this one

What is a good way to change the brightness and contrast in an
NSImage?

I've been playing with the vImage library for changing contrast,
using the vImageEndsInContrastStretch. This works, but how does
one return the contrast to it's original value? you
specify that 0% of the pixels lie at the histogram extreme,
you can't get the original values back. I know of the ImagApp
example showing how to use CIImage, but using that would require
a re-write of quite a bit of code I'd rather not go there.

Too bad, because that's how to do it.

-jcr

John C. Randolph <jcr (AT) mac (DOT) com(408) 914-0013
Roaming Cocoa Engineer,
Available for your projects at great Expense and Inconvenience.


>>
>
>Do not post admin requests to the list. They will be ignored.
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>>
>This email sent to dave (AT) criticalpath (DOT) com
>>
>

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K I've gone to the CIImage.

Next question: I can create a CIImage from NSBitmapImagRep, but all
I can get from the CIImage is an NSImageRep this has no method for
getting at the bitmap data. I'm using a CIImage, how do I get
the bitmap data?

Thanks again,
Eric

Dec 3, 2005, at 7:30 PM, Dave Camp wrote:

I think the problem is it isn't clear what you are asking for

Are you asking for pointers to general brightness and contrast
algorithms?
Are you asking how to get at the NSImage bitmap data to manipulate
it yourself?
are you asking if there are other Apple supplied frameworks that
will perform brightness and contrast adjustments for you?

Dave

Dec 3, 2005, at 8:04 PM, Eric Smith wrote:
>
>CIImage wasn't even around until 10.4 there must be a way to
>handle this from an NSImage. Anyone out there use brightness and
>contrast controls on an NSImage, or the bitmap data associated
>with the NSImage?
>>
>Thanks,
>Eric
>>
>Dec 2, 2005, at 9:34 PM, John C. Randolph wrote:
>>

Dec 2, 2005, at 9:29 PM, Eric Smith wrote:

I've been going around in circles with this one

What is a good way to change the brightness and contrast in an
NSImage?

I've been playing with the vImage library for changing contrast,
using the vImageEndsInContrastStretch. This works, but how does
one return the contrast to it's original value? you
specify that 0% of the pixels lie at the histogram extreme,
you can't get the original values back. I know of the ImagApp
example showing how to use CIImage, but using that would require
a re-write of quite a bit of code I'd rather not go there.

Too bad, because that's how to do it.

-jcr

John C. Randolph <jcr (AT) mac (DOT) com(408) 914-0013
Roaming Cocoa Engineer,
Available for your projects at great Expense and Inconvenience.


>>
>
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>>
>This email sent to dave (AT) criticalpath (DOT) com
>>
>

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Dec 3, 2005, at 7:46 PM, Eric Smith wrote:

Question: how do people typically deal with this problem? Keep
an original bitmap around in case one wants to reduce the contrast
(get back all the original information) ?

That's how we did it before CoreImage, yes.
-jcr

John C. Randolph <jcr (AT) mac (DOT) com(408) 914-0013
Roaming Cocoa Engineer,
Available for your projects at great Expense and Inconvenience.

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I've been wondering why this is so difficult, and I think that the
answer is that all of this stuff is meant to be done in the display
pipeline. If you want the bits back, you can probably use -[CIContext
createCGImage:fromRect:]. If you are in the NSImage world, you can
render into an NSImage and pull back the bits by creating an
NSBitmapImageRep from the NSImage data:

image = [[NSImage alloc] initWithSize:NSMakeSize(width, height)];
[image lockFocus];
[[NSGraphicsContext currentContext]
];
[[self adjustedImage] drawInRect:NSMakeRect(0, 0, width, height)
fromRect:NSMakeRect(0, 0, [self image_width], [self image_height])
operation:NSCompositeCopy fraction:1.0];
imageRep = [[NSBitmapImageRep alloc]
(0, 0, width, height)];
[image unlockFocus];
data = [imageRep
properties:nil];
-Kenny

Dec 3, 2005, at 9:39 PM, Eric Smith wrote:

K I've gone to the CIImage.

Next question: I can create a CIImage from NSBitmapImagRep, but
all I can get from the CIImage is an NSImageRep this has no
method for getting at the bitmap data. I'm using a CIImage,
how do I get the bitmap data?

Thanks again,
Eric

Dec 3, 2005, at 7:30 PM, Dave Camp wrote:
>
>I think the problem is it isn't clear what you are asking for
>>
>Are you asking for pointers to general brightness and contrast
>algorithms?
>Are you asking how to get at the NSImage bitmap data to manipulate
>it yourself?
>are you asking if there are other Apple supplied frameworks
>that will perform brightness and contrast adjustments for you?
>>
>Dave
>>
>Dec 3, 2005, at 8:04 PM, Eric Smith wrote:
>>
CIImage wasn't even around until 10.4 there must be a way to
handle this from an NSImage. Anyone out there use brightness and
contrast controls on an NSImage, or the bitmap data associated
with the NSImage?

Thanks,
Eric

Dec 2, 2005, at 9:34 PM, John C. Randolph wrote:

Dec 2, 2005, at 9:29 PM, Eric Smith wrote:

I've been going around in circles with this one

What is a good way to change the brightness and contrast in an
NSImage?

I've been playing with the vImage library for changing
contrast, using the vImageEndsInContrastStretch. This works,
but how does one return the contrast to it's original value?
you specify that 0% of the pixels lie at the histogram
extreme, you can't get the original values back. I know of the
ImagApp example showing how to use CIImage, but using that
would require a re-write of quite a bit of code I'd rather
not go there.

Too bad, because that's how to do it.

-jcr

John C. Randolph <jcr (AT) mac (DOT) com(408) 914-0013
Roaming Cocoa Engineer,
Available for your projects at great Expense and Inconvenience.

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>>
>

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Dec 3, 2005, at 10:02 PM, Kenny Leung wrote:

I've been wondering why this is so difficult, and I think that the
answer is that all of this stuff is meant to be done in the display
pipeline.

It's probably worth mentioning at this point that this can probably
be done with no code at all, using a QC composition, and a QC Patch
Controller.
-jcr

John C. Randolph <jcr (AT) mac (DOT) com(408) 914-0013
Roaming Cocoa Engineer,
Available for your projects at great Expense and Inconvenience.

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