Muted color when adding pages from PDF but not when opening PDF

[Seejay]

I have a printing workflow where many pages are generated as PNG (with transparency) in an application outside Affinity. The easiest way to get these into my afpub document is to convert the images to a multiple-page PDF (using PDF24) and then use the "add pages from file" in afpub. However some (not all) of the colors seem to be getting muted by the last step in that workflow. The target document's color space is CMYK (Coated FOGRA39).

The pure magenta highlight color you see below is correct when the source PDF is opened in afpub or acrobat:

That magenta highlight color is defined as RGB=255,0,255 in the source application.

Below is how the image looks in Affinity Publisher after "add pages from file".  If I copy a single page manually from the opened PDF (with correct highlight color) and paste it into the destination afpub document, I get the same result.

The source PDF, when opened in afpub using the "estimate" color setting ends up as sRGB, so my assumption is that it is the conversion to CMYK that is doing this and there's nothing to be done. But if there are other things to try, I'd be happy to hear them. 

My grasp of this whole CMYK conversion business is tenuous, but I wonder if I could somehow reverse engineer the correct RGB values to set for the highlight color in the source application that would be interpreted as CMYK=0,100,0,0 on conversion?

Many thanks.

[Seejay]

It may also be worth noting that the other colors in the document seem to be translated well and display the same regardless of how viewed. It's just this pure magenta that is getting messed up.

[firstdefence]

Simply dragging the top png into an afpub document will also result in the muted magenta, what is the source app you are using?

[Hangman]

Hi @Seejay and welcome to the forums,

Your assumption that it is the conversion to CMYK that is doing this and there's nothing to be done is pretty much correct... RGB=255, 0, 255 is way outside the gamut of Coated FOGRA39 as shown here...

RGB=255, 0, 255 appears in the far right corner of the sRGB profile which is way beyond a colour achievable using CMYK and in this case, Coated FOGRA39 which is why you see the muted colour since RGB=255, 0, 255 is converted to the closest value possible within the gamut of Coated FOGRA39 which is a much more muted Magenta.

Colours from your RGB source file which fall within the gamut of FOGRA39, i.e., where the two profiles overlap (shown on the right) will produce a much closer match when converted between the two different colour spaces...

sRGB Left | Coated FOGRA39 Middle | sRGB Overlayed onto Coated FOGRA39 Right

Out of interest, how are the graphics shown in your original post actually created, do they exist in vector form at any stage of the process?

[Seejay]

1 hour ago, Hangman said:

sRGB Left | Coated FOGRA39 Middle | sRGB Overlayed onto Coated FOGRA39 Right

That is a helpful graphic. Thanks for sharing it. One of the reasons I chose magenta as the highlight color is that I thought it would be easy to get a bright, clear version of it with CMYK = 0,100,0,0 but I guess you can only get so much magenta on the page.
 

Quote

Out of interest, how are the graphics shown in your original post actually created, do they exist in vector form at any stage of the process?

The graphics are generated in Bricklink Studio. It has both PNG and PDF outputs, but in either case the graphics are rasters, not vectors. 

For now, I think my solution is to just use a different highlight color. 

Thanks again for the inputs. 

[lacerto]

While it is generally true that the color gamut of (s)RGB is wider than that of (typical coated) CMYK, it is good to acknowledge that there are tones within CMYK that cannot be reproduced in sRGB -- in fact, one of the reasons Adobe created Adobe RGB was to get better display predictability for CMYK jobs than when using mere sRGB. This naturally also requires that the monitor supports wide gamut. This clip demonstrates how colors are clipped when converting from Coated Fogra 39 to Adobe RGB (practically not at all) and sRGB (note that on the forum, all colors are truncated to sRGB so the demonstration is not realistic but conceptual, showing that there is a difference):

 It is also good to note that when using the CMYK color mode within Affinity apps, the out-of-sRGB colors of the active CMYK color space are not shown because the CMYK mode is limited to sRGB (this can be experienced also when spot colors are used, as their representation in CMYK color mode is limited to sRGB).

As for OP's case (practically just tones of magenta), what is mentioned in posts above about these kinds of tones getting truncated when converting to / simulating CMYK target is certainly true, and the additional notes mentioned related to difference of RGB and CMYK color gamuts are basically irrelevant.

[Seejay]

But still helpful in terms of my unerstanding, so thanks.