Acrobat color conversion: DeviceGray vs DeviceN "Black" CMYK (0, 0, 0, 1)
When exporting to PDF with InDesign CC 2015.4 using the default PDF/X-4 preset, grayscale images filled with the default solid Black swatch (100K, Uncoated FOGRA29) are exported as DeviceGray, unless somewhere in the layout there also exist a partially transparency vector object using the same black, in which case those grayscale images are exported as filled with DeviceN: "Black" CMYK (0,0,0,1) instead. Is there a way to control this, or a reason for it? Is there any way, with Acrobat or a free command-line tool, to replace the DeviceN: "Black" CMYK (0,0,0,1) black of grayscale images with DeviceGray? Why do I care: When using Acrobat DC 2015 to convert all colors to sRGB (Tools > Print Production > Convert Colors > Convert colors to output intent: sRGB), Acrobat maps the black of vector objects filled with the default solid black (100K) to black RGB (0,0,0), and does the same with the black of DeviceGray grayscale images. All blacks in those PDFs consistently become 0,0,0 RGB. But if grayscale images were exported as filled with DeviceN: "Black" CMYK (0,0,0,1), their black is converted to RGB muddy gray, and therefore color conversions of layouts containing both vector objects and grayscale images, both filled with solid black, produces inconsistent RGB blacks. Just to clear up: my purpose is not obtaining color-accurate RGB conversions of CMYK solid blacks, but getting RGB blacks that are pleasant for screen viewing, i.e. 0,0,0 RGB. That, I already get from 100K-filled vector objects when converting colors as described above, but not from grayscale images filled with DeviceN: "Black" CMYK (0,0,0,1). I do understand CMYK solid blacks do not match in fact their color space's black point, and therefore that a color-accurate conversion should produce RGB muddy grays, and I can indeed also get Acrobat to do that for all 100K, be them from vector objects and from grayscale images filled with DeviceN: "Black" CMYK (0,0,0,1), by using Acrobat's "Conversion Attributes" color conversion options instead of "Convert Colors To Output Intent". But what I want them to be is consitent 0,0,0 RGB.
Here is a set of files illustrating the issue: https://cl.ly/1a1v0m0v2127 • `image.tif` is a 100% black grayscale image. • `DeviceGray.indd` is an InDesign document (idml also provided) containing the image plus an opaque vector object filled with the default 100K Black. Exporting using the preset PDF/X-4 generates `DeviceGray.pdf` which uses DeviceGray for the grayscale image. • `DeviceN.indd` is an identical InDesign document except for the fact that the vector object is given partial transparency. Exporting using the same PDF preset generates `DeviceN.pdf` which uses DeviceN: "Black" CMYK (0,0,0,1) for the grayscale image instead of DeviceGray. Using Acrobat to convert colors to sRGB (Tools > Print Production > Convert Colors > Convert colors to output intent: sRGB) provides consisted RGB 0,0,0 blacks for both the vector object and the grayscale image in `DeviceGray.pdf` but not in `DeviceN.pdf`. On Tue, Dec 20, 2016 at 11:21 AM, Jorge . <chocolate.camera@gmail.com> wrote:
When exporting to PDF with InDesign CC 2015.4 using the default PDF/X-4 preset, grayscale images filled with the default solid Black swatch (100K, Uncoated FOGRA29) are exported as DeviceGray, unless somewhere in the layout there also exist a partially transparency vector object using the same black, in which case those grayscale images are exported as filled with DeviceN: "Black" CMYK (0,0,0,1) instead.
Is there a way to control this, or a reason for it? Is there any way, with Acrobat or a free command-line tool, to replace the DeviceN: "Black" CMYK (0,0,0,1) black of grayscale images with DeviceGray?
Why do I care:
When using Acrobat DC 2015 to convert all colors to sRGB (Tools > Print Production > Convert Colors > Convert colors to output intent: sRGB), Acrobat maps the black of vector objects filled with the default solid black (100K) to black RGB (0,0,0), and does the same with the black of DeviceGray grayscale images. All blacks in those PDFs consistently become 0,0,0 RGB.
But if grayscale images were exported as filled with DeviceN: "Black" CMYK (0,0,0,1), their black is converted to RGB muddy gray, and therefore color conversions of layouts containing both vector objects and grayscale images, both filled with solid black, produces inconsistent RGB blacks.
Just to clear up: my purpose is not obtaining color-accurate RGB conversions of CMYK solid blacks, but getting RGB blacks that are pleasant for screen viewing, i.e. 0,0,0 RGB. That, I already get from 100K-filled vector objects when converting colors as described above, but not from grayscale images filled with DeviceN: "Black" CMYK (0,0,0,1). I do understand CMYK solid blacks do not match in fact their color space's black point, and therefore that a color-accurate conversion should produce RGB muddy grays, and I can indeed also get Acrobat to do that for all 100K, be them from vector objects and from grayscale images filled with DeviceN: "Black" CMYK (0,0,0,1), by using Acrobat's "Conversion Attributes" color conversion options instead of "Convert Colors To Output Intent". But what I want them to be is consitent 0,0,0 RGB.
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Jorge .