One of our most common questions being sent in to the helpdesk is, what are JPG artifacts and why are my images being rejected for this reason?
WHAT ARE JPG ARTIFACTS?
JPG artifacts are areas of distortion in an image, often with the distortions resembling a blocky pattern. JPG artifacts can result from too-much image compression that discards some image data. JPG, as an image format, causes the loss of image quality, especially after editing/saving/ or re-opening JPGs in an image editor. There are several different types of JPG artifacts, although the differences between them are discussable. Also, JPG artifacts can often be mistaken as ISO noise, and the difference between the two distortions are sometimes near indiscernable.
Artifacts are often most visible around edges, so in people shots, often around the eyelashes or other areas of hair is generally a danger zone for artifacts.
An extreme example of JPG artifact distortion @ 100%
This image displays minor hair JPG artifacts @ 100%. Taken in a studio with a Canon 1ds Mark III. Artifacts can happen even at the best of times.
WORKFLOW FOR AVOIDING JPG ARTIFACTS:
Step 1. Shoot in RAW. Always. Definitely, the first thing to do in avoiding artifacts is to stop shooting in JPG. For wedding photographers or journalists who need a streamlined workflow to deal with a large amount of images quickly, JPG artifacts are maybe not such an issue. However, in stock photography, there is the luxury of dedicating time to images to achieve the highest technical quality.
Step 2. Turn off any in-camera sharpening. Sharpening images will increase artifacts. A very limited amount of sharpening in post can sometimes be recommended though.
Step 3. Never underexpose images too much. Its true that exposures can be adjusted in RAW during post, but, along with it comes the risk of artifacts.
Step 4. Develops RAWs as 8-bit TIFF files for re-touching any editing on the image. TIFF is a loss-less and uncompressed format so it is possible to save and re-save without increasing artifacts.
Step 5. Save the final and edited copy of image as a JPG at the highest quality setting. If any further editing of the image is required, refer to the TIFF file and avoid re-opening the JPG.
NOTE: Its recommended to check for artifacts in Photoshop as some image viewers use an interpolated zoom that will not display pixels very accurately, making artifacts hard to discern.
The Crestock team will be available to discuss this further under this forum topic. Look forward to hearing from you.