0

You can convert an RGB image into grayscale in Photoshop easily.

16 RGB colours

Here's a swatch of 16 colours. The values of the colours are important.

However, later versions of Photoshop add noise to the image.

grayscale

The image now has 41 colours. The noise was NOT in the source image, created by hand.

If we look closer at one of the colour swatches you can see it better: I've increased the contrast - for clarification.

grayscale close up

There are many ways to remove colour from an image. As there are ways to remove noise. That's not what I'm asking.

Using Photoshop, is it possible to convert to grayscale without the seemingly additional noise?

Image > Mode > Grayscale > No Noise, thank you.

6
  • I cannot reproduce your results, I didn't get any noticeable noise when converting the color swatch to Grayscale. Could this be from compression when exporting to a JPG? Can you use a black & white adjustment instead of changing the color mode?
    – AndrewH
    Apr 1 at 12:56
  • Even your B&W image doesn't have a lot of noise when zooming in, nothing like your 3rd image.
    – AndrewH
    Apr 1 at 12:57
  • Anyway if you want noisless exports do not use JPEG
    – joojaa
    Apr 1 at 13:08
  • @joojaa - who said anything about JPEGs?
    – Ghoul Fool
    Apr 1 at 13:10
  • @GhoulFool your example image is a jpeg. YOu can also not make examples jpegs
    – joojaa
    Apr 1 at 13:11
7

The image in your post already contains noise/artefacts — maybe it's because it was compressed by GDSE. Here's one of the image channel compressed with Levels:

enter image description here

If your original image doesn't have this noise and contains only pure colors, the issue you have is probably with color profile. Default color setting in Photoshop has a Use Dither conversion option — this results in the noise you see. Also if you're converting from sRGB image make sure you're using Gray Gamma 2.2 profile for correct lightness.

enter image description here

Here I remade your image with pure colors:

enter image description here

Converting to Grayscale with Use Dither set to on, noise is visible after compressing the colors:

enter image description here

After converting to grayscale with Use Dither set to off no noise is present:

enter image description here

0

The problem is almost certainly caused by JPG artifacts in your original image. I concur with the others who have responded here. I checked and can see them in your coloured image, so they are already there, although not really visible until you apply levels/curves/equalize or try to manipulate the colours.

Don't edit JPGs in Photoshop unless you have no other choice. Instead, create your original image as a PNG or PSD instead. When you use JPGs, the images undergo lossy compression. These compression artifacts are pretty normal for JPG, it's why JPGs can be so small. JPG artifacts can get much worse when you try to change colours/edit stuff. Also every time you save a JPG it adds more compression and more artifacts.

The JPG format should only really be used as a final output format, for example for photographs on web pages, or for print. Because of this problem, editing JPGs is something you should really never do if you are looking for quality results. Don't use them for small web graphics either. Save these in a lossless format instead, such as PNG.

Also note that if you are uploading a PNG image as an icon/avitar or images for social media sites, these are often converted to JPG by the website/app. Social media sites such as Facebook and Instagram also convert PNGs to JPG, and this can cause quality issues.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.