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I took a picture in colour and while playing with some settings accidentally changed it to black and white. Before I knew what I did, it saved. How can I change it back to colour? Please help!!

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    \$\begingroup\$ Is it RAW or another format such as JPG ? Did you used a software to change the image (which one) ? \$\endgroup\$
    – Olivier
    May 3, 2017 at 16:37
  • \$\begingroup\$ You changed it in your camera or later on your computer? JPEG or RAW? \$\endgroup\$
    – Michael C
    May 3, 2017 at 16:37
  • \$\begingroup\$ I believe it is in jpeg and it turned black and white in the camera and then saved. The picture was taken as colour. I cannot find a second copy of the image in the camera \$\endgroup\$
    – Krystal
    May 3, 2017 at 16:39
  • \$\begingroup\$ Did you use the Retouch menu's Monochrome setting? Have you looked at the files on the card on your computer? Or just on your camera? \$\endgroup\$
    – inkista
    May 3, 2017 at 17:38
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    \$\begingroup\$ @Itai I don't think this question is a duplicate of the proposed. I think this has more to do with recovering the color version of the file in the D5100, where the "original" is stored side-by-side with the in-camera converted B&W. That is, I think so, based on the existing answer. But I do think this qualifies as "unclear what you're asking", though. \$\endgroup\$
    – scottbb ♦
    Sep 1, 2017 at 15:35

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If you convert the colour image, which is represented as w x h x 3 matrix with Red, Green and Blue "layers", into B/W image, which is represented by w x h matrix and and it is ovewritten, there is no way back.

It is like somebody irons your 3D origami into 2D shape. You have transformed 3D object to 2D object; you have lost one dimension.

The simplest algorithm to convert RGB image to B/W uses pixelwise operation:

V[i,j]=(r*R[i,j]+g*G[i,j]+b*B[i,j])/(r+g+b)

where r, g, b are scaling factors and R, G, B are the values in the original matrix.

As you can see, if you want to reconstruct, say, the red layer, you have to know all the B/W image (you have it), scaling factors (you can find them, or expect them equal to 1) and both green and blue layers (which you do not know).

Dig your card, maybe there is some undeleter tool, if you shoot to both RAW and JPEG there is slight chance you have affected only one or you have set the camera to interpret RGB RAW image as B/W one.

If I were you I'd expect the worst and shoot the picture again, if possible.

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    \$\begingroup\$ Actually, reading the D5100's user manual, processing in-camera after shooting to be monochrome should retain both the color original and the new B&W image. The OP stated the image was shot in color. \$\endgroup\$
    – inkista
    May 3, 2017 at 19:54
  • \$\begingroup\$ This makes sense too. Ihe camera allocates memory for 3D object. It would need to allocate new memory for 2D object and then unallocate the former one. Applying B/W filter to is seems much easier. \$\endgroup\$
    – Crowley
    May 3, 2017 at 20:00
  • \$\begingroup\$ @inkista Agreed. On the 3200 (the only Nikon model I've ever used those "after effects" on) the camera stores both the original and the edited version alongside each other on the card. \$\endgroup\$
    – wally
    Aug 2, 2017 at 7:43

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