Re: imshow problem under OS X

[Carnë Draug]

On 9 March 2015 at 15:07, Marius Schamschula <address@hidden> wrote:
> Carnë
>
> On Mar 9, 2015, at 9:48 AM, Carnë Draug <address@hidden> wrote:
>
>> On 9 March 2015 at 14:10, Marius Schamschula <address@hidden> wrote:
>>> Carnë,
>>>
>>> On Mar 9, 2015, at 6:11 AM, Carnë Draug <address@hidden> wrote:
>>>
>>>> On 9 March 2015 at 11:03, Marius Schamschula <address@hidden> wrote:
>>>>>
>>>>> The GraphicsMagick issue is separate from the imshow issue: I get a 
>>>>> warning
>>>>> regardless of if GraphicsMagick is built with a depth of 8 or 16 bits.
>>>>>
>>>>
>>>> As you should. You will not have a warning if you build it with 
>>>> quantum-depth 32
>>>> (but then all your images will take 4 times more memory during the reading 
>>>> and
>>>> writing --- but not after the reading or writing).
>>>>
>>>> Carnë
>>>
>>> Thanks for the clarification.
>>>
>>> The MacPorts default is 8 bit. When I checked the Octave wiki [1], it
>>> suggested to pass --with-quantum-depth=16 to configure. I rebuilt
>>> GraphicsMagick with this setting and again saw the warning. The wiki
>>> needs to be updated.
>>>
>>
>> No it does not.  Unless you really have 32bit image files, you do not want
>> to build with quantum depth 32.  And even if you, I'd recommend you use 2
>> different builds, one with 32 and another with 16 (or maybe 8).
>>
>> If you build with quantum-depth 32, your images will take up 4 times more
>> more memory during the reading.  And that's the uncompressed size.  Using
>> quantum-depth 16 is a good compromise, it will keep the vast majority of
>> users happy without causing a massive memory overhead.
>>
>> I wrote some text on the wiki's Debian page about it [1]
>>
>> Carnë
>>
>> [1] http://wiki.octave.org/GraphicsMagick#Quantum_depth
>
> I also think 16 bits should be enough.
>
> However, I find the warning message a bit confusing, especially for end
> users. Is there a way to disable this message?
>

The warning is important because it is not obvious that the build option of
GM will cause this limitation.  Even worse, GM will automatically adjust the
intensity values on the image so users may not even realize they are losing
data.  And even with quantum depth 32, it behaves weirdly for images with
floating point values.

With 4.0.0-rc1, this warning has the ID "Octave:GraphicsMagic-Quantum-Depth"
so you can just turn that one off.

Carnë