A RAW Comparison

To see if there were any notable differences between the RAW and JPEG formats when processing underexposed and overexposed images, a test was conducted. In a series of images, the test subject was underexposed by 1 exposure value (EV), 2 EV, and 3EV, and then overexposed by 1EV, in both the RAW (.NEF) and in the JPEG file formats.

In processing, the requisite exposure value (+/- EV) necessary to bring each image back to correct exposure was made. For example, if an image was underexposed 1 EV during capture, then it was processed at +1 EV. The RAW files were processed in Adobe Camera RAW (ACR), and the JPEG images were processed in Photoshop CS. Then sections of the images were compared at 100%.

A Nikon D70 six megapixel camera, and a Nikkor AF 20-35mm EDIF F/2.8 lens (at 35mm)were used for the test. The aperture was f/16, and the ISO rating was 400, on all shots. The images were made in Aperture Priority mode, with Matrix metering. The camera and lens were mounted on a Gitzo tripod, and the lighting on the test subject was natural directional lighting from the left side. The JPEGs were taken at the largest file size (same size as the .NEFs) with the detail setting at "normal".

The only variable in the compared images at any given exposure value (EV) was the format: one was RAW (.NEF) and the other was JPEG. After the test images were processed, they were viewed in Photoshop CS at 100%. Four different areas of the subject were sampled and compared. The table below, Figure 1, reveals the amount of increase or decrease in exposure value (EV) each sample received during capture and during processing.

SAMPLE	PROCESSING EV	CAPTURE EV
1	+1 EV RAW	-1 EV RAW
2	+1 EV JPG	-1 EV JPG
3	+1 EV RAW S	-1 EV RAW S
4	+1 EV JPG S	-1 EV JPG S
5	+2 EV RAW	-2 EV RAW
6	+2 EV JPG	-2 EV JPG
7	+2 EV RAW S	-2 EV RAW S
8	+2 EV JPG S	-2 EV JPG S
9	+3 EV RAW	-3 EV RAW
10	+3 EV JPG	-3 EV JPG
11	+3 EV RAW S	-3 EV RAW S
12	+3 EV JPG S	-3 EV JPG S
13	-1 EV RAW A	+1 EV RAW A
14	-1 EV JPG A	+1 EV JPG A
15	-1 EV RAW B	+1 EV RAW B
16	-1 EV JPG B	+1 EV JPG B

Figure 1.

The test subject was the Quaker Oatmeal box in Figure 2. The samples selected from the images processed at, and labeled, +1,2,3 EV, were made for midtone comparison. The samples selected from the images processed at, and labeled, +1,2,3 EV S, were made for shadow comparison. And, the samples selected from the images processed at, and labeled, -1 EV A and -1 EV B, were made for highlight comparison.

Figure 2.

Samples from Test Images at 100%

(EV During Processing Noted)

+1 EV RAW (Sample 1)	+1 EV JPG (Sample 2)


+1 EV RAW S (Sample 3)	+1 EV JPG S (Sample 4)


+2 EV RAW (Sample 5)	+2 EV JPG (Sample 6)


+2 EV RAW S (Sample 7)	+2 EV JPG S (Sample 8)


+3 EV RAW (Sample 9)	+3 EV JPG (Sample 10)


+3 EV RAW S (Sample 11)	+3 EV JPG S (Sample 12)


-1 EV RAW A (Sample 13)	-1 EV JPG A (Sample 14)


-1 EV RAW B (Sample 15)	-1 EV JPG B (Sample 16)

Observations

1. The underexposed RAW and JPEG files, which were corrected during processing, each reveal different levels of noise directly proportional to the degree of their respective underexposure. However, at any given level of underexposure, the noise was more noticeable and pronounced in the 8 bit JPEG files, than it was in the 12 bit RAW files.

2. In both formats, at any given level of underexposure, noise was more noticeable and pronounced in the shadows, than it was elsewhere in the image.

3. When the 8 bit JPEG test image was overexposed 1 EV, lost highlights could not be recovered during processing. See, Samples 14, 16. When the 12 bit RAW test image was overexposed 1 EV, at least some of the highlights were recovered during RAW conversion. See, Samples 13,15.

< back to article >