48bit Image Colour Issues When Saved as JPEG

When I edit images in Photoshop that are either created in Photoshop, or from a scanner, I usually deal with 48bit images. I like the extra overhead for editing that 48bit images provide. The one problem that I encountered recently was saving the file to a JPEG to be displayed on a Web site. The problem was the colours of the image were off and the image looked dull and had a lack of contrast.

After reviewing my workflow when saving a 48bit to a JPEG to display on the Web I quickly realized my mistake. I explain my mistake in this post and how I corrected it.

Colour Profiles

Although I work mainly work in Photoshop for all my image editing, this section can be used by almost all image editing. This section wil discuss colour profiles.

Devices, such as scanners, printers, and monitors, have a colour profile associated with them. A colour profile is a file that is stored on your computer and contains all the colour information for a device. These profiles ensure that the colours in your image wlil appear correctly when used by the device.

For this post, I will mainly talk about two colour profiles: Adobe RGB (1998) and sRGB since these are the two I mainly use when editing images. When I create an image or edit a 48bit image I work with the Adobe RGB (1998) colour profile. When I have 24bit images, such as JPEGs, I usually work with the sRGB profile. The reason for this is that the Adobe RGB (1998) contains many more colours defined in its profile than sRGB so it can handle the higher bit images. sRGB is mostly used for display images on the Web and computer monitors in general.

Unless you save the image correctly with the right profile, your colours will not look good when going from Adobe RGB (1998) to sRGB.

This is where my problem comes in.

Converting to a Profile

As I mentioned above, the problem I had was with the image colours. When I saved the image for Web viewing the colours became dull and the entire image lacked contrast. Once I went over my workflow I realized my problem.

When I saved the image as a JPEG it was still using the Adobe RGB (1998) profile and was 48bits. When the image was saved as a JPEG it attempted to save the exact same colours as the 48bit image, but unfortunately it was only a 24bit image so some colours couldn’t be displayed correctly.

I then went back to the 48bit image and converted the colour space to sRGB:

Photoshop CS2 and CS3

  1. Click Edit->Convert to Profile.
  2. Under Destination Space select sRGB IEC61966-2.1.

Photoshop CS and earlier

  1. Click Image->Mode->Convert to profile.
  2. Under Destination Space select sRGB IEC61966-2.1.

You image will now be converted to the sRGB colour space with the colours in the image being matched as closely as possible to that colour space.

You can now save your image as a JPEG and it will appear as close to the original in terms of colours a possible.

Summary

I recently had colour issues when saving a 48bit image in the Adobe RGB (1998) colour profile as a JPEG. The problem was the fact that I didn’t convert to the sRGB colour profile before I saved the image. Once the image as converted to the sRGB colour profile the colours appeared as close to the original as possible.

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