python image convert rgb transparent turns black

Then you would have to manually adjust the CMY inks and overprints until you have invented a set of colors where equal amounts of ink gives a neutral color. You would have to enter Ink Options > Ink Colors > Custom.: The only way I can see for you to force the darkest colors to CMYK(20, 20, 20, 100) using Custom CMYK is quite hacky. That's more than you allow in the darkest part of the image, so the transitions in the image might end up looking rather strange and some kind of banding might occur. This can make it easier for the printer if you have large areas, but as the darkest point in an image, it's quite low.Ī bright red color in the image might be around CMYK(0, 100, 100, 0) so it has a total ink of 200%. The total ink of your custom rich black is only 160%. It differs from color profile to color profile. Uncoated paper usually allows 260-300% total ink and coated paper 300-340%. This is normally a thing you try to avoid. You are trying to force the darkest part of the images to have a specific non-neutral color, so you are (unintentionally?) trying to use CMYK conversion to change the perceived color. See here how an RGB black converted to CMYK (darkest possible neutral color) compares to your custom rich black when proofed with different color profiles:Ī CMYK conversion will try to maintain the colors of the original.

Your color will have a slight color tint depending on which standard the print house follows. The CMY inks does not have the same properties so mixing them equally will not create a neutral color. This seems a little random to me (although I know that it's common practice for many). You have chosen a rich black with the values (20, 20, 20, 100). In other words: If you don't know which CMYK profile your print house use, you can't do a proper RGB to CMYK conversion and you can't trust the preview on your screen! Your custom rich black isn't neutral The only way Photoshop can show us a preview on screen is because it knows (or assumes) which CMYK color profile is in use. So if your screen is calibrated according to a standard (often sRGB or Adobe RGB) and the print house has calibrated their equipment according to a standard, Photoshop is able to show you a (more or less) precise preview showing how your CMYK colors would look on print. Each print house decides which standard they are going to follow (for each device, paper type etc.) and calibrate their equipment to match. They are mainly based on measurements on actual physical prints, not theoretical assumptions. This is why color profiles were invented. A CMYK color is not an objective color, it's simply a set of technical instructions for the printing device on which halftone percentages to use. Since there are different printing devices, different kinds of paper, different inks and different ways to calibrate the equipment etc., the same set of CMYK values will look different on different setups. The whole idea with RGB to CMYK conversion is to create a CMYK image which on print will look as similar as possible to the original RGB image.

Python image convert rgb transparent turns black