imagemagick7, MagickCore: GetPixelChannels(image) not valid after PingImage()?

[jcupitt]

Hi all,

I'm rewriting an import class for imagemagick7, lots of nice improvements, thank you.

I'd like to be able to call PingImage() and then get the number of channels with GetPixelChannels(image), but this seems to return 0, at least for JPEG images. It seems I can only use GetPixelChannels() after ReadImage().

Is this correct? Is there any way to get the number of channels without decoding the whole image?

[magick]

You could try calling InitializePixelChannelMap(image), before you call GetPixelChannels(). The channel map is initialized when the pixel cache is initialized. The pixel cache is generally not initialized when you are "pinging" an image. Let us know if that works. If so, we will consider adding a patch to initialize the pixel channel map automatically when pinging an image.

[jcupitt]

It works! And it makes PingBlob() work too.

Thank you very much. I have another question, I'll start a fresh topic.

[dlemstra]

We added a patch so you won't need to do it yourself in the next version: http://git.imagemagick.org/repos/ImageM ... 85e97aa69d

[jcupitt]

I've found a case when this fails. If I PingImage()/InitializePixelChannelMap(image) on a PDF I see:

image->depth = 16
GetImageType() = 6
GetPixelChannels() = 3

But if I ReadImage() the same file I see:

image->depth = 16
GetImageType() = 7
GetPixelChannels() = 4

I'd obviously like Ping and Read to return the same header so I can allocate memory correctly. Is there some way around this?

[magick]

Thanks for the problem report. We can reproduce it and will have a patch to fix it in GIT master branch @ https://github.com/ImageMagick/ImageMagick later today. The patch will be available in the beta releases of ImageMagick @ http://www.imagemagick.org/download/beta/ by sometime tomorrow.

[jcupitt]

Works well here. Thank you very much!