Photoshop 24 bit image showing black pixels in 8 bit mode

Question

I came across this problem after printscreening a website with a gradient background. Initially, I was shocked to find that the background was showing those black pixels, and thought something might be wrong with my GPU so I decided to investigate a little and found out that the image's bit depth was 24 and photoshop was opening it in 8bit mode (maybe because photoshop doesn't have a 24bit mode?).

I was wondering: How come when I save the image in 8bit mode it doesn't show those black pixels, in programs like windows photo viewer and paint? Why are they showing only in photoshop? Shouldn't photoshop find comparable colors to fill in instead of black?

When I change the mode to 32bit those black pixels disappear. Also, when sampling those black spots with the eyedrop I am getting the correct color.

This is the image I was speaking about:

And here's what I am seeing:

Answer 1

It was a problem with my GPU driver. I have an ATI HD7950 and I upgraded the driver to version 13.1 which apparently caused this issue with photoshop. the fix is to either downgrade the driver to version 12.8 or upgrade to the beta driver (13.2) I hope this would help anyone having the same issue.

Answer 2

This is a long shot, but the black pixels you're seeing aren't out of gamut warnings, are they?

These occur when you have set a print/output colour space for the image that is different to the image's native colour space and some of the areas in the image fall outside the print colour space. If the image is wide gamut like Adobe RGB and it thinks it needs to output to a different colour space, deep blue-green colours are likely to fall outside that colour space.

If it is this (and I am still not very confident it is, until I see a screenshot) then these are warnings only and can be turned off within Photoshop (by disabling proof colours, perhaps?)

As Scott says, 24 bit is just another way of saying 8 bits per colour so it's not that.

Answer 3

8bit = 24 bit.
It's merely a different way of displaying it.

8 Bit means 8 bits per channel.

8 Bits per channel means 8R 8G 8B (8x3) = 24bits.

Photoshop merely uses the former which is why the menu in Photoshop reads "8 bits / Channel"

What it sounds like you are referring to is a 32bit image. 32bit images also have 8bits for alpha (transparency). 24 bit images do not have transparency.

Photoshop can have trouble with some formats. And you can lose transparency depending up how you grabbed the image. If transparency isn't transferred, Photoshop will substitute black, hence black in Photoshop where transparency should be. Most often it's due to a color being set as transparent in the image. Many apps allow you to define the color for transparency. Photoshop does not, and due to that, can fail to interpret that setting.

GIF images are notorious for losing transparency when opened with Photoshop. But it's a common thing with PNG24 images as well if an app strips enough metadata from the png, Photoshop won't read the transparency. The solution is to pen the image and resave it in a desktop application which does see the transparency. Afterward Photoshop generally displays the image correctly.