R: Re: understand ImageType, ClassType and ColorspaceType

Hi,
Thank you very much for your reply.
Could you help me understand if my reasoning is correct?
Can I have two possibilities:
1) If I have a PseudoClass image then I will have a single channel defining 
the index to the colormap. In this case the depth-per-sample is identical to 
the depth-per-pixel
2) If I have a DirectClass the depth-per-sample will be equal to a quantum 
size and the number of channels is 4 by default, even if the alpha channel can 
be ignored.
Thanks again.
Paolo Pazziani



>----Messaggio originale----
>Da: [email protected]
>Data: 11/04/2013 16.03
>A: "[email protected]"<[email protected]>
>Cc: <[email protected]>
>Ogg: Re: [GM-apis] understand  ImageType, ClassType and ColorspaceType
>
>On Thu, 11 Apr 2013, [email protected] wrote:
>
>> 
>> Hi, I would like to know what's the meaning of enumerators ImageType, 
ClassType and ColorspaceType.
>> 
>> In this regard, I read the documentation of the page http://www.
graphicsmagick.org/api/types.html
>> 
>> What combinations of these three enumerators can be found? In particular in 
some tests I have noticed that
>> different types of images (Grayscale, black and white, RGB, BGRA) provides 
always the same ColorSpaceType that is
>> sRGBColorspace.
>> 
>> Furthermore after reading images with 32 bit per pixel when the number of 
colors is low ImageType=PaletteType,
>> while in the case of high number of color ImaType=TrueColorType
>> 
>> There is a deterministic way to know the original and the current type? 
There is a more comprehensive
>> documentation?
>
>The confusing thing about these properties is that they report 
>GraphicsMagick's opinion about the image as it is loaded into memory 
>and does not really have anything to do with the input file format. 
>It has more to do with the subformat automatically selected when the 
>image is saved than the input file subformat.
>
>For example, the input file might be in a 'RGB' storage format, but 
>the pixels are actually only gray levels.  In this case, the ImageType 
>would be reported as GrayscaleType.
>
>If the image is represented in PseudoClass (color-mapped) format, then 
>it will be reported as PaletteType or PaletteMatteType.  However, a 
>simple enumerated field (Image 'storage_class') can be changed so that 
>such images may be instantaneously switched to TrueColorType or 
>TrueColorMatteType.  GraphicsMagick is able to support both 
>color-mapped and direct representation of pixels at once, but only one 
>representation will be used at once.  If any image processing has been 
>done on an image which was originally color-mapped, it is likely to be 
>converted to DirectClass representation since it is most appropriate 
>for image processing.
>
>ColorSpaceType is most likely to be reported as RGBColorspace rather 
>than sRGBColorspace since the sRGBColorspace is peculiar to Kodak 
>PhotoCD format.  If the input format has only one sample per pixel 
>then it may be reported as GRAYColorspace.
>
>GraphicsMagick supports a huge number of input formats.  When a file 
>is read, the data is normalized into the internal representation. 
>Almost all knowledge of the input format is then lost.
>
>Bob
>-- 
>Bob Friesenhahn
>[email protected], http://www.simplesystems.org/users/bfriesen/
>GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/



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