Re: Acrobat color conversion: DeviceGray vs DeviceN "Black" CMYK (0,0,0,1)
Re: Acrobat color conversion: DeviceGray vs DeviceN "Black" CMYK (0,0,0,1)
- Subject: Re: Acrobat color conversion: DeviceGray vs DeviceN "Black" CMYK (0,0,0,1)
- From: "Jorge ." <email@hidden>
- Date: Tue, 20 Dec 2016 11:30:33 +0100
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 . <email@hidden>
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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