DRO vs. ACR vs. IDC

October 14th, 2008 - 09:16:00 PM:

Dynamic Range Optimizer (DRO) is a feature of Sony's Alpha DSLRs to handle high-contrast situations better. RAW converters offer similar functions. Here's a short comparison of these tools. The contenders are:

• Sony α700 with DRO level 3
• Adobe Camera Raw 4.5 (ACR)
• Sony Image Data Converter 2.0.01.09280 (IDC)

Update October 18th, 2008:

I've updated this test to also include the following RAW converters:

• Bibble Lite 4.3.0
• Raw Therapee 2.3
• CaptureOne 4.5

Update October 24th, 2008:

I've added two more RAW converters:

• Silkypix 3.0.25.1
• DxO Optics Pro 5.3

Update October 29th, 2008:

• Added comments regarding Lightroom 2.1

Here's the scene and the resulting pictures:

Full frame
Straight conversion	DRO Level 3
ACR with fill light	DRO in IDC
Bibble Lite	Bibble Lite with CA correction
Raw Therapee	CaptureOne
Silkypix	DxO

The straightly converted RAW file is nearly unusable. This is what you get when you have a high-contrast scene and don't want to blow out the highlights. When you adjust exposure to retain detail in the sky, the shadows are very dark. This is what DRO was invented for. The basic idea is to expose for the highlights and then post-process the image to lift the shadows. The α700 has several DRO modes, and I was using manual level 3.

When you convert the RAW file with ACR, you can use the “fill light” or “shadow/highlight” function, which basically does the same. It lifts the dark parts of the image without blowing out the highlights.

Alternatively, you can use IDC to convert the RAW file and use the DRO settings in IDC. While these settings are also called “DRO”, it's obvious that these are implemented differently.

I was trying to get similar results from all conversions, but the different limitations and different implementations lead to different results, namely:

In-camera DRO:

The shadows are lifted nicely, but the entire picture lost contrast. The grass in the middle really looks dull.

ACR:

The image looks nice, and I have to admit I have also adjusted contrast and saturation a bit.

IDC:

I was using the extremes of the DRO settings and also adjusting exposure and contrast, but still couldn't get the same amount of shadow fill as with in-camera DRO or ACR. It was not possible to get proper fill and not also brighten up the sky a bit. But at least the result is not as dull as with in-camera DRO.

Bibble Lite:

I was also using the extremes of Bibble's fill settings. The result is between ACR and IDC. The shadows were lifted a bit more than with IDC, but a brightening of the sky was unavoidable.

Raw Therapee:

It was really hard getting the result that you can see here. It took me nearly half an hour, and then it was impossible to scale the image down to 500 pixels without totally destroying it. In the end I was scaling it first to 1000 pixels and then to 500 pixels in a second step. Once I managed to do it the result looks good.

CaptureOne:

I simply couldn't get the fill that I wanted. I always ended up with either blown out sky, dark foreground or very low contrast. The above is a compromise.

Silkypix:

With Silkypix there is no dedicated fill light function, so I was using the gamma correction and contrast sliders. I didn't get better results with the gradation curve function. As can be seen, I didn't get enough fill light without washing out the sky. The original nice blue sky is simply gone.

DxO:

Using DxO to crack this hard nut was not easy. After downloading more than 300 MB (!) I found that it has no dedicated fill light function, and the gamma slider only yielded over-contrasty greenish rubbish. I had to resort to the tone curve function to lift the shadows. But I had to give reds an extra lift. Otherwise I would only get the same greenish image as with the gamma correction function. In the end the result was at least acceptable.

All conversions might pass off as usable, except probably the one from CaptureOne.

But now let's look at a crop of the branch in the top left corner:

Crop of top left corner
Straight conversion	DRO Level 3
ACR with fill light	DRO in IDC
Bibble Lite	Bibble Lite with CA correction
Raw Therapee	CaptureOne
Silkypix	DxO

Now the results look quite different:

In-camera DRO:

CAs are increased a bit, but otherwise it's OK.

ACR:

This is horrible! CAs are magnified over the top. This is something you hardly notice in the scaled down version, but now that you know it's there you can even see it there.

When using ACR in Lightroom, where CA correction is available, the result is improved only marginally. The cyan/magenta fringe is turned into a near-gray fringe, but it's still a fringe several pixels wide.

IDC:

DRO in IDC also keeps CAs under control, but also reaches its limits before filling in the same amount of light as with ACR or the camera's DRO. You can barely see details on the branch, and the leaves are still nearly black.

Bibble Lite:

Again, the result is similar to IDC, i.e. the shadows are lifted a bit more. By default, CAs increase a bit more. I've also done a second conversion with Bibble's CA correction feature. With this it's possible to reduce CAs to make them invisible. But it comes with a price…

Raw Therapee:

I was using the CA correction feature, and this crop also looks fine. However, in the top left corner you can see a hint of something that I couldn't get rid of. It looks like strong luminance noise, but luminance noise reduction couldn't remove it without destroying the rest of the image. Also, a vertical stripe turns up in the top right corner. Two crops from that area look like this:

Crop of top right corner
Raw Therapee	Raw Therapee

This is really, really bad. This can only be a problem in RT's demosaicing algorithm. Also the Windows Image Viewer has problems opening the original file.

CaptureOne:

The built-in CA correction (with auto detection) worked really well. Also note how much detail is preserved!

Silkypix:

CAs are well controlled with the CA correction function. The detail level is somewhere in the middle.

DxO:

CAs are well corrected (DxO comes with a lens profile for the Carl Zeiss 16-80). But in the middle tones you can see a big problem. These are often converted into grey, contrast-less patches. Here's another crop from the top right corner which shows this problem better:

Crop from top right
DxO

The only way to get rid of this was to not lift the shadows, which, of course, defeats the purpose of this test.

Now some more crops, this time from the center:

Crop of center
Straight conversion	DRO Level 3
ACR with fill light	DRO in IDC
Bibble Lite	Bibble Lite with CA correction
Raw Therapee	CaptureOne
Silkypix	DxO

In-camera DRO:

The in-camera DRO dropped a lot of the contrast of the original image, and with it a lot of apparent detail and sharpness.

ACR:

Good contrast and sharpness

IDC:

As already mentioned, I had to increase exposure with IDC, otherwise the darker foreground would have been just too dark. Contrast is OK, but the image appears less sharp than the other two.

Bibble Lite:

Again, results are similar to IDC (sharpening was set a bit lower). When CA correction is used, however, you lose considerable detail. So what you win at the edges you lose in the center.

Raw Therapee:

The center crop looks fine.

CaptureOne:

As in the corner crop there is a lot of detail in the center, but contrast is quite low. But looking closer to the foreground things don't look so good:

Crop from center bottom
CaptureOne

The leaves on the ground look washed out and without detail, as if I had used a soft focus lens. This section looks a lot better with the other converters.

Silkypix:

Nothing spectacular there.

DxO:

Also nothing special to mention here.

Conclusion

It looks like there is no clear winner. ACR produces the best fill, but horrible CAs. In-camera DRO is too flat. IDC and Bibble Lite don't allow the fill I wanted, either blowing out the sky or leaving the foreground in the dark. Raw Therapee offers nice fill, but has massive problems otherwise (broken JPEGs). CaptureOne is probably best in sharpness, but worst in fill. Silkypix also leaves something to be desired with regards to fill, but otherwise is OK. DxO handles CAs well, but that's about it. The strange artifacts it produces are simply a turn-off, and that after filling your hard disk.

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