Exporting/Printing documents with multiply effect.

[n33z]

I was hoping someone could diagnose this one:

I created a document which has various coloured elements created in illustrator, with a black and white jpeg placed on top. I applied the multiply blending mode to the jpeg in order to make the white areas of it transparent and retain the black. This looks perfect on screen, but when I either export the document to another format (PDF, JPG, whatever) or print it the black areas of the JPG become slightly different tones depending on the colours of the vector based elements behind it.

I thought this may be something to do with the "overprint and transparency flattener options" but for some reason it will only let me change the resolution setting, and not the "Overprints" setting which is stuck on "Preserve".

I don't know whats goin on. If anyone can shed any light on any of this it'd be much appreciated. Thanks.

 

[apepp]

...is this jpeg a black and white image. i.e. solid black for image on a white background?

Is the jpeg cmyk black or just greyscale (black only) in photoshop?

...if it is black only channel then the multiply layer option will act as overprint, therefore the colours the black and white image is sat on top of will be added to the black, depending on the values it is sat on, this is the nature of multiply effects...

...if it is a cmyk jpeg the same will happen, adding more ink underneath the cmyk image colour values, though not as noticeable as just having a black only image sat on top, because there is more ink involved...

...you can test this using the eye dropper tool and click on different areas of the blacks in the image, they will all read differently i expect, because the image has a multiply effect to it, colours underneath come into play with this on...

...depending on your version of illustrator you can now view black more accurately with a setting in the preferences, there is also an overprint preview option under view, quite handy, but again depending on your version of illustrator...

...depending on how different the ink values are in your cmyk readings you might well get away with overprint black, but it sounds in your case you will need to even up those cmyk values in the image that is sat on top, you will need to do this in photoshop, making it a cmyk black, rather than just black ink or greyscale...

...this is also known as underpinning...

...if possible save it as a bitmap tiff (not greyscale) and import it into illustrator and then colourize it, this depends on the image you have though, and may not be a suitable option...

...if not your best opiton is to make it a richer cmyk black in photoshop and re-link it back into illustrator...

andrew

 

[apepp]

...just to add, if going to a commercial press, your bitmap tiff will need to be at least 600 dpi to maintain crisp edges, for example type on a logo...

...this may require a bit of photoshop trickery to achieve an acceptable result if your image is currently only 300 dpi and positioned in illustrator at 100% scaling...

andrew