Some Raw Truth about RAW Converters
Your RAW conversion program may be damaging your image
Until recently, I held RAW conversion programs as basically sacrosanct. I realized that I was confusing that feeling with the purity of the RAW image itself. The idea is that the RAW image is the pure CCD image, so when we ask for it from our camera, and through whichever RAW converter we’re using, we expect a faithful version of the RAW image.
As it is, all RAW conversion programs must do some work to get the image to you. Demosaicing, some limited auto-levels, and typically a gamma curve. Added onto that is some color balancing, and perhaps some other functions.
But, after what should be innocuous operations, we expect a RAW file that is not just fairly representative, but very faithfully representative of the RAW image. That’s why we use RAW.
Many RAW editors — free and expensive ones both — will actually damage your image before you even see it, in many ways.
In Part I, I discuss Black and White points in the histogram, as well as range compression. These are issues a RAW conversion program should handle carefully, and it turns out that many don’t.
This article is for Sagelight users and non-Sagelight users alike. For Sagelight users, this article answers a question that comes up every once-in-a-while: “How come my (automatically processed) RAW image looks plain compared to other RAW conversion programs?“. For non-Sagelight users, this can tell you what to look for in your preferred RAW conversion program, whatever it is.
How I Ended Up Getting on my Soap Box about RAW conversion
The other day, a user sent me a couple images converted from their original RAW format. One was a Sagelight image, and the other was from a fairly expensive package. When I looked at the two pictures, I didn’t need to look at the labeling to see which one was from Sagelight and which one was from the other package.
With the Sagelight image, I saw exactly what I expected: A well-formed histogram without range compression on either side. By now, I think it’s probably obvious that the user liked the other image better. After making a convincing argument that Sagelight was doing it right, and this other RAW conversion program had, in fact, irreparably damaged their image, I decided to write an article on it.
This isn’t the first time I went through this time-consuming process of convincing someone that their RAW converter damaged their image, but it was the first time I decided to take a look at a number of RAW conversion programs to see what is going on under the hood with these things. It’s been a known factor that Sagelight does things differently than a lot of RAW editors, and this is for a reason. Not so much to be different, but because most RAW editors take liberties with your picture that they shouldn’t.
Before I researched it, I didn’t realize the extent to which many RAW conversion programs will damage your image before you even see it.
I’m from the old school of things, I guess. Sagelight, like many editors, makes many assumptions about pictures to help you along with your image and to make things easier. Sagelight takes the viewpoint of not doing anything for you automatically that will harm your image, such as cutting black-and-white points too much. But every editor is different, and they should be. There’s enough room for many editors in this field. But, RAW images… Well, that’s a different story.
All Raw Converters Are Not Created Equal
With RAW, however, I thought all editors were the same. With Sagelight, I make the assumption that if you’re using a RAW image then you’re serious. Otherwise, you could just accept the JPEG from the camera after it has done a host of image processing functions on it — after all, even with a 24-bit JPEG there is still plenty of room to edit your picture and make it look more to your own liking.
By definition, RAW is much more about subtlety. It’s the little things that give you the room for expression. RAW has a higher dynamic range as well as a higher bit-depth. With RAW, you also get more control. The normal in-camera processing takes away this control from you. With RAW, I want to control the sharpening, the noise reduction, the auto-levels, and anything else that can make a different in my picture.
After all, you wouldn’t take an expensive sports car and put 87 octane gas in, would you? RAW is the same way — if you’ve bothered to go through the steps to get the sports car, then you also assume the mechanic you take it to won’t just treat it like a regular car.
What I found with RAW Converters
After going through this with a number of users privately, I decided to look into a number of RAW converters — some free and some very expensive. In many cases, I found some significant issues that contradict the entire reason we use RAW in the first place.
I will be discussing 5 different programs in this article, Program A, Program B, Program C, Program D, and Sagelight. All of these are retail programs (some expensive and well-known), except for one which is a free but, surprisingly, scored better than the other A-D retail programs in the list. For the record, I did not test Adobe products, mostly because many people who use other editors, including Sagelight, do so to find an alternative to Adobe or because Adobe Photoshop just costs too darn much.
The RAW portions of Sagelight were written with the old-school mentality of not doing anything more than is necessary to the image, and then giving you the control to back out of it or change whatever Sagelight is doing.
RAW images start in life as very dark pictures, and it’s necessary to do some operations — like Gamma curves and some levels adjustment — before you see the picture. After that, with a RAW image, an editor should be doing nothing. It’s your picture, and your options should not be limited by destructive behavior.
First, let’s look at the two pictures I was sent plus another editor that was referred to in the letter. The first from Program A:
A little dark, but realistically, this is more typical of what a RAW image really looks like before it a gamma curve is applied — most RAW images look very dark natively.
Now, that’s a pretty good looking picture. It has fairly nice contrast. Maybe a little dark, but definitely better — from a visual perspective than Program A
Well, this doesn’t look nearly as nice as the picture from Program B, does it? Nor should it!
Let’s see why. Let’s take a look at the histograms:
Programs A& B have damaged this image in a significant manner. On both the histograms for programs A & B, the black points have been cut off completely. This can cause problems. The low point data, especially when at 16-bits per-channel, is very valuable, and this data is now gone in the RAW conversions from Programs A & B.
Let’s look at what can be recovered here:
In this image, since Sagelight kept this data, we can recover a lot of the shadow information to make a nice even picture. This data is either lost or so highly compressed as to be essentially unrecoverable with programs A & B.
I will get to this in the next example, but as you can see Sagelight has preserved the upper highlights. It’s just a little red line, but sometimes this can make all of the difference in a picture. Much of the time, since the histogram represents the entire picture, this data is fairly meaningless.
However, in other cases, this also represents a focal point — a specular reflection that will become completely flat.
In this case, visually, the sample from Program B looked the best. It may have damaged the picture for some editing, but since it looks better, how much will it take to get Sagelight to look as good or better? Simple: One slider movement in the RAW editing mode (the contrast slider):
After one slider movement, we have the same picture as Program A — but better. Notice that the background, though dark, is still visible. It was cutoff in both program A and B. You can’t see it here, but the textured board of the background is completely visible in this image. Also, we can still recover the dark areas near the scarf to create an image with a much broader dynamic range.
RAW pictures have much more dynamic range than you would think, especially after the treatment with some RAW conversion programs. Here are two samples, one from Sagelight, and one from Program A, which happens to be a very well-known, expensive package:
The image to the right represents the blown highlights in this image based on the each color channel. As you can see, its quite extensive. In the orange banner to the left-center of the picture, for example – it looks fine, but is actually blown out in the reds. if you wanted to change the texture of this area you would run into problems,
This was the impetus for writing this article. This RAW conversion would normally make you think these areas were blown out in the RAW image when they are perfectly intact:
Here, the Sagelight version — again looking less visually interesting for the moment — has absolutely no blown highlights, as shown in the image to the right.
Program B also had similar blown highlight problems, but not as many as Program A.
Let’s look at a side-by-side comparison:
As you can see, in the picture to the left, the brownish tiles above the doors and windows are completely blown out and unrecoverable — they are simply gone and blown out from the image data. You can also see that the upper sky area, nice and blue in the Sagelight image, is also blown out and white. Even areas that are still blue suffer from a range-compression issue making them basically unrecoverable. The highlights on the girl’s shirt are also becoming blown out.
I leave it as an exercise that the Sagelight image can be made into the more visually impressive image — sans blown highlights on the wall and in the sky — with a simple Contrast Slider movement in Sagelight.
Highlights and Range Compression
Let’s look at the histograms for Programs A, B, and Sagelight for this image:
With Program A, it’s clear that the highlights are blown in this histogram and that this data is unrecoverable. With Program B, it’s also clear that some highlights are blown (but not as many as Program B).
With the Sagelight image, you can see two things: The right edge of the histogram has a nice, natural slope downward showing that this image has a full range of highlights that don’t need to be cut off.
Also, you can see that the histogram is moved inward a little on both sides. This is because there are some low-level shadows and highlights that are too minimal to be displayed in the histogram.
Sagelight is preventing two things here:
1. Cutting off Specular Reflections
By not cutting off the very top of the unseen — but, nevertheless, existing — highlights, Sagelight is preventing what could be a specular highlight from becoming flat. This can be a reflection off of a window, sunglass, or somewhere else — one of the major elements that gives a picture depth, or, conversely, makes a picture seem flat.
2. Range Compression
Range Compression is not a subject that is generally discussed with image editing, but this is a problem that makes it difficult to deal with highlights that are still present in the image. First, non-16-bit-per-channel editors have little chance here. Second, this is where terms like “Highlight Recovery” come from — the idea of getting this compressed data uncompressed in the histogram.
It’s better to just avoid it in the first place, at least where possible.
Even though most of the highlights are present in the histogram of Picture B, it’s still very difficult to deal with the compressed highlights. In many cases, it’s just not practically possible and where it is possible, it’s a lot of work — and it’s still hard (if not impossible) to get the same results you’d get if they weren’t compressed in the first place.
Coming in Part II
In part II, I show more destructive tendencies of some RAW conversion editors, which were even more surprising to me than what I’ve showed here in part I. I will show where some conversion programs smooth, sharpen, and otherwise modify your image in ways that are not only destructive, but once again contradict the reason you’re using RAW in the first place.
RAW editors have become somewhat sacrosanct in our minds, because RAW images are properly sacrosanct. Until recently, I thought that was true (with the RAW editor part). But, I found that many RAW converters — some very expensive and popular — aren’t treating your images they way you might think and, in many cases, are actually damaging your image and limiting what you can achieve.