High Resolution JPEG Quality and Sagelight

caesium-color-0

Introduction

This article discusses the high quality of saving with JPEGs in Sagelight.  I recently wrote a blog article about how you can edit images with most JPEG images (i.e. images coming from your camera as JPEGs) without fear of creating results that don’t compare to RAW images, and showed how you can easily (more easily, in fact) get the same overall results as many RAW images – as long as the JPEG quality was very high.

This discussion is just about that: High JPEG Quality in Sagelight, what it is doing, why Sagelight does it, and most importantly, the differences between the utmost quality (as practiced in Sagelight) and saving for lower file sizes.

I want to point out that this issue is not about Sagelight.  I am sure Lightroom and other high-end image editors save out in the same quality.  This is about photographic editing vs. utilitarian saving for file-sizes.

This post is about being educational about what a photographic editor like Sagelight does with saving your JPEG image vs. various utilities out there.  There are reasons to do both – save for higher quality with the higher file sizes that come with it, and to also save for lower file sizes that causes loss to your image quality (but often not enough to care about for such purposes).

For storage, internet, and overall editing, it is important to save with higher quality.  However, this is not always the case, and this tends to be outisde the scope of a “Photographic” or “Digital Darkroom” editor, at least in the main settings, which is why it is great that so many great and wonderful utilities exist outside of editors like Sagelight.

This discussion came up on the discussion board recently, and I thought it was worthhwhile to discuss it as a blog post.

High Quality vs. Low Quality

Let’s return to this image:

caesium-color-0

To save this image in the best JPEG quality Sagelight or any other photograhic/digital darkroom editor should always look visibly identical — at the pixel level — to the original image when it is reloaded.  It’s not technically identical, but visually we shouldn’t be able to see any detectable differences with most images.

For example, there really is no point in showing a before-and-after image for a highest-quality JPEG image, because it would and should look exactly the same as the image above!

Color Loss and File Sizes

Some editors and utilities save with less color definition to keep the file size small.  This is called 4:1:1 or 4:2:2 vs 4:4:4, explained below. Sagelight and other photographic editors like Lightroom save in 4:4:4 JPEG to maximize the color quality.  This leads to larger file sizes than some other editors that don’t do this, but the quality difference is clear”:

caesium-color

The above image was saved in non-4:4:4 (probably 4:2:2), and the color loss in the image is clear (the image was gamma adjusted to be more visible).  The above is the color lost by not saving in high quality color, and the color kept by editors like Sagelight, Lightroom, and others.

By now, you might be asking why I keep mentioning Lightroom and other editors.  This is because this issue is not related to Sagelight specifically, but editors made for photographic quality vs. saving jpegs for filesize and utility purposes.

What is 4:4:4, 4:2:2, and 4:1:1?

4:4:4 is the highest quality.  This means for every Light and Color element (there are 2 color channels and one light channel) a corresponding value is saved in the JPEG – it might be lossy, but these values are considered and kept in the JPEG file.

jpeg444

4:2:2 simply means that only every other color channel pixel is kept, and the rest is simply thrown out, as seen in the diagram below.

jpeg422

4:1:1 means that for every 4 color elements, only 1 is kept, and 3 out of 4 color elements is thrown out.

jpeg411

4:2:2 and 4:1:1 will lead to smaller file sizes, and since color distortions are harder for the human eye to detect than luminance values (which is why the Y/Luminance channel always has 4 values, one for each pixel), the result can often can look the same as a higher quality (4:4:4) image.

However,  there are certainly problems associated with lower color quality.

Color Sub-sampling example

When a process samples only some of the pixels, rather than all of them as with 4:4:4, it is called sub-sampling.  Sub-sampling in the color channels (i.e. 4:2:2 and 4:1;1) causes visible problems, even at the highest quality JPEG level — this is because some color data has been destroyed prior to compressing the image for the JPEG.

jpegsub1

4:4:4 example

jpegsub2

non-4:4:4 example (probably 4:1:1)

In the above example, you can see how the colors start to bleed from box to box.  If you’ve ever wondered why reds and other bright colors become so blurry on televison, this is why – it’s usually 4:1:1.

The above is an example of how the image starts to deteriorate when non 4:4:4 is used.  Even though it tends to look good, it is actually not working well for the image, which can cause noise and other problems. When other things happen to your image, such as sloppy resizing, further edits, crops, and then further resaving, this can cause more and more problems for your image.

 

Representing your Image Well after the Save

Resizing and Saving as a JPEG: Resize Utilities vs. Photographic Editors, Lanczos and other Resize Methods

Sagelight is about representing your image well at all times, whether it is saved in lossy JPEG or resized.  At first, some of the little things that happen with low color, resize, or overall JPEG quality may not seem like an issue.  But, they do make a difference, even when subtle.   Little color problems, blurriness, and artifacts all come together to make your image less powerful and evocative – it might not be completely visible, but an image can come out a little more dull or less clean-looking with small problems subtly getting into your image.jpegdiff

The above example is very subtle.  In many ways, it is hard to tell the difference. But if you look closely, you can see color bleeding and blurry details.

This is for two reasons:

1. Resizing

Resizing with methods that aren’t as accurate or sharp can lead to smaller file sizes, but can also create details not nearly as sharp as the original.  Sagelight uses Bicubic, Bilinear, and Lanczos resizing.  Sagelight defaults to Lanzcos because it tends to be sharper and more accurate, representing your original image much better even when it is resized to smaller dimensions.

If you step back a little from your monitor, you can see how the bottom image is a little blurry.  This is because it was resized with a method that does not keep details – this lends itself to smaller file sizes,  but, even when it is smaller, it does not represent the image well – and Sagelight is all about making sure your image is represented in the highest quality.

2. Color bleeding.  You can see the color bleeding in this image.  They eye might not notice this right away, but it does make a difference when you’re looking at it even from a distance.  It doesn’t necessarily register on the eye, but it does make an overall difference with your image.

Re-Editing

Saving in higher quality also means you can re-edit the image.  For example, the above images were actually reloaded from the discussion board, cropped and re-saved because it was just easier than reloading the originals.  This was possible because the images were saved in 4:4:4 high quality – even when you are not using the ‘best’ quality (i.e. 7,8, or 9), you can still re-edit the image for cropping and small touch-ups.

Conclusion

Saving JPEG images with 4:4:4 high quality also means higher file sizes. In today’s world, this means a minimal difference between each file size.  In the above example, the difference was 117k vs 200k, which is no longer an issue when Internet bandwidth is very high, Flickr offers a terabyte, and the standard hard drive is now about 4 Terabytes.

Sagelight, along with other photographic/digital darkroom editors, choose 4:4:4 as the highest quality so that your image doesn’t degrade and presents itself well in any situation.  Small nuances of color bleeding, artifacts, and blurry/soft edges make your image look duller – and when you resize it and save it to put out to the web or your personal viewing,

Sagelight wants your image to look the best possible.

Various utilities work to keep smaller file sizes that also sacrifice quality.  Such utilities are very useful.  The purpose of this blog post is to point out the differences and to be more educational so that you can know what is going on with Sagelight and other editors vs. various programs out there, so you can decide what is best for your images.

There are also some great utilities out there, and this isn’t to denigrate any such product, but to help in the understanding of photographic editing and saving vs. more utility-based programs out there that do a wonderful job – for what they mean to do vs. what Sagelight means to do.

 

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s