Hi, this my first post to this forum...
I have created an advertising flyer in Photoshop 7.0 which is basically photographs of our products on a white background. The source artwork was prepared at 600dpi. I provided the artwork to the printers saved as a CMYK pdf. The artwork looked great on screen and looked OK when printed out on our fairly mediocre postscript colour laser printer.
When the flyer came back from the printers I was very disappointed with the result:
1) The edges of the products where surrounded by a lot of very visible stray dots/noise. i.e. It looked like there was a swarm of midges flying around edges of the products
2) A fairly solid yellow area on one of the product pictures was also speckled with the same dots/noise.
I confronted the printer about the poor quality and after investigation they said this was because the noise existed in the source document.
When I went back to look at the source artwork I did find that there was a scattering of pixels with 1% to 2% dot density around the edge of the products (but invisible on my good quality monitor).
Also, the yellow area which was approximately 100% Y + 25% M, also contained some pixels with 1% C. i.e. 100%Y + 25%M + 1%C. But again on my monitor, as one would expect, the yellow area looked perfectly clean with smooth tonal variation.
I have done some research and understand that these 1% pixels are often referred to as scum dots. I also understand that these scum dots and noise can be introduced by the profile used for the RGB to CMYK conversions. I also appreciate that high jpeg compression ratios can introduce this type of pixel noise. (Incidentally, although the product images were originally jpegs they were of a high quality and not heavily compressed).
So, I understand basically how these 1-2% pixels can get into an image. But, the questions I really want answered are:
1) Is it correct that pixels with only 1%-2% dot density in the source image should come out in print as *very* visible speckles, when these pixels appear white on a computer monitor, and are also invsible when the image is printed on our postscript laser printer?
2) Should the yellow area of the image look similarly covered in "black" speckles just because some of the pixels are defined as 100%Y+25%M+1%C?
3) If these 1-2% pixels really can cause this level of visible speckling then whose responsibility is it to ensure the source artwork is appropriately "cleaned" so that hard copy is noise free, as seen on computer monitor? Is it my responsibility or the responsibility of the print shop? BTW, the equipment used for printing was described to me as a letterpress machine.
BTW, we have used the same product images in an A3 poster that was printed out on a professional wide format inkjet poster printer. There was no such noise visible on this A3 poster.
Any help with understanding what's happened here would be greatly appreciated.
