The mysterious 70% tint in Photoshop

[Gregg]

Totally stumped by Photoshop's inability to produce a 70% tint of any of the process colors. Create a CMYK file (size and resolution are unimportant). Fill your canvas with 70% Magenta. Now place the eyedropper on the canvas and you will see that Photoshop reads the color as 69% Magenta. The same is true for CYK, as well as any combination of them. For example, a fill of 70/70/70/70 will read 69/69/69/69.

This "bug" seems to only affect a 70% tint. If I created a 69% tint, it would read as 69%. If I created a 71% tint, it would read as 71%.

Any clue why this is happening? For the record, I have tried this is CC, CS6, CS5, all with the same result.

 

[Dov Isaacs]

It is not a bug at all, but rather, a difference between the way vector and text color values are specified versus color values for raster images. For vector and text, color values are expressed as decimal values from 0.0 to 1.0. On the other hand, for raster images, values are integer values ranging from 0 to 255. Thus for a vector or text object, 70% tint is 0.7. For raster images, a 70% tint is 0.7 times 255 or 178.5. Since the value is a decimal value 178.5 is truncated (not rounded) to 178. The decimal equivalent of 178/255 is 69.8. Photoshop truncates the decimal to provide you with a value of 69%.

- Dov

 

[Joe]

It reads 70% for me in CC 2015.

 

[gordo]

It reads 70% for me in CC 2015.

69% rather than 70% for me (PShop CC 2015.1.1).

Dov! Fix the selection tool! No other apps have the problem PShop has (e.g. ghost selections)

 

[Magnus]

Interesting! Had to try it (Mac Ps 2015.1.2) and I get 69% aswell..

 

[chrisg42]

As Dov indicated, it is impossible to have exactly 70% in an 8-bit image. There are 256 steps between 0% and 100%.

Try this in Photoshop:

Create a CMYK 8-bit image.

Fill with 70% M

Check with eyedropper - 69% as previously described.

Now create another image, but this time CMYK 16-bit.

Fill with 70%M

Check with eyedropper - 70% !!

This is because the 16-bit image provides 65,536 steps between 0% and 100%, so can specify 70% more or less exactly.

 

[Gregg]

Thanks, everyone. This has been an interesting one for sure. Joe, can you confirm that your document was 16-bit?

 

[Joe]

Thanks, everyone. This has been an interesting one for sure. Joe, can you confirm that your document was 16-bit?

Yes as shown here:

 

[Gregg]

That's 8-bit. The mystery continues...

 

[Joe]

OK if I just 'Fill' the image with 70% of all colors it shows 70%.

If I fill it with the Paint Bucket tool it reads 69%.

 

[benstarr]

OK if I just 'Fill' the image with 70% of all colors it shows 70%.

If I fill it with the Paint Bucket tool it reads 69%.

I just got the same thing in CC 2015 (16.1.1), very strange.

I understand the explanation however I wonder why would Adobe choose to display 69.8 as 69 instead of 70, I'd think it would make more sense to round the numbers up or down for display instead of truncating them. This truncation leads to both 69% (176/255) and 70% (178/255) being displayed with the same value, it also makes 99% display as 98%.