Re: Move rgb2ntsc and ntsc2rgb to image package

[Rik]

On 01/17/2018 09:32 AM, Carnë Draug wrote:
> On 17 January 2018 at 16:22, Rik <address@hidden> wrote:
>> On 01/17/2018 07:20 AM, Carnë Draug wrote:
>>> [...]
>>> Finally, the reshaping back to the original shape can be done with the
>>> existing private function colorspace_conversion_revert [2].
>> I tried using that function at first, but had to give up because I couldn't
>> get ND-images to work correctly.  The problem is that, unlike rgb2ntsc, the
>> third dimension is removed.  I can't mimic that by just deleting the
>> dimension from the sz vector because colorspace_conversion_revert expects 4
>> dimensions.  The code in question is
>>
>>     if (is_nd)
>>       rv = reshape (rv, [sz(1:2) sz(4) sz(3)]);
>>       rv = permute (rv, [1 2 4 3]);
>>
>> We could recode this to be more general, or we could just make rgb2gray a
>> one-off function.  I'm inclined to do the latter, but if you see a strong
>> reason for modifying colorspace_conversion_revert we could do that.
>>
> The thing is that in a grayscale image, the 3rd dimension must be one,
> the 4th dimension can't simply be shifted to the 3rd dimension like it
> is happening now on core.  The test unit for ND images is also
> incorrect.  I have attached a diff that fixes it.

Go ahead and push the changes.  I thought the singleton dimension would
have been squeezed out, but I don't work with images much so I'm apparently
wrong.

--Rik