Is Camera Preview a JPEG?


Today’s Question: I’ve heard photographers say that you can’t really read too much into the preview on your camera’s LCD display because it is a JPEG image even if you are shooting raw. Is that true, and if so how does it impact the preview you’re seeing?

Tim’s Quick Answer: It is true that the image preview on the LCD display of your camera is essentially a JPEG preview of the raw capture. But I feel it is misleading to call it a JPEG image, and inaccurate to suggest you can’t “trust” this JPEG preview.

More Detail: The reality is, you’re never truly viewing a raw capture. After all, a raw capture is simply a collection of values representing electrical impulses measured by the image sensor based on the amount of light striking each photodiode on the sensor during an exposure. That information must be translated to actual pixel values, such as the RGB (red, green, and blue) pixel values used to define colors and tonal values in a digital photo.

In order to view a raw capture, the raw data needs to be interpreted. That could mean actually processing the raw data to render a new image, such as when you use Camera Raw to render a raw capture to an image in Photoshop.

With other software, such as Lightroom, you are viewing either a JPEG preview (such as in the Library module) or a real-time rendering of the raw data (in the Develop module). In this situation you are still viewing an interpretation of the raw data, not the actual raw data. All software that is able to process or preview a raw capture is interpreting the data, resulting in a slightly (or significantly) different result.

Similarly, the image you see on the camera’s LCD display is essentially based on in-camera raw processing. Think of it as having a little version of Adobe Camera Raw built into your camera. The raw capture data is processed in the camera to render what is essentially a JPEG image. But much like a raw capture processed with Camera Raw in Photoshop, this in-camera preview is based on the raw capture.

In other words, the preview you see on the camera’s LCD display isn’t inherently inaccurate. It is a rendered preview of the capture data. In-camera settings (such as contrast and saturation) will affect that preview. In some ways this enables you to have a preview on your camera’s LCD display that might be closer to your final intent for the image than what you would initially see in Adobe Lightroom or Bridge, for example.

So, the preview on the camera’s LCD display is just that: a preview. That preview can generally be counted upon to give you a good sense of what will be possible with the final image. To me what is more important is the histogram, so you have a sense of whether you’re losing highlight or shadow detail to the point that you won’t be able to recover that detail in post-processing.

The preview may not be completely accurate relative to the initial image you’ll see in your workflow on the computer, or relative to the final result you’ll achieve when interpreting the image with various adjustments. But I certainly wouldn’t say that you can’t “trust” the in-camera preview for your captures.