If you are like me that keep a detailed trading journal in a blog or in
a computer, then capturing technical analysis charts (assuming you use
TA) is an essential historical record of your trades. I was saving my
charts in JPG format for many years because that's also what my digital
camera used. So I used it without giving much thought. It wasn't until
one day when I realized my saved charts were slightly blurry that I gave
the issue of image format more thought. After some research, I found out
that not all image formats are created equal. Not only do they differ in
compression level, they also differ in their quality and intended use.
This post is intended to summarize my conclusion about why PNG format is
the best for saving stock chart captures. In addition to the popular
JPEG image format, I have often seen other technical analyst bloggers
use GIF to post their charts. As such, I'll compare the 3 formats in
this article. The criteria for judging image format for stock charts are
obviously quality and file size. Quality is definitely what matters the
most because stock charting relies heavily on the points and lines for
comparison and analysis. If you can't figure out the resistance/support,
for example, from looking at the image, then that chart couldn't provide
you with in-depth analysis later. Which would render it useless for the
purpose of reviewing your trades. As for file size, it depends on if
you're posting it online. If that the case, then it's arguably as
important as the quality of the image. Waiting for images to load is an
unnecessary waste of time. Before digging deeper in this topic. I
figured that it's best to just present a real case trading journal
example. Here's what I did for the figures attached below. I captured a
chart of crude oil futures with my trading screen. Moving averages,
channels, volume, and a couple more separate indicators. A pretty
typical setup. The first image is saved in JPG format. It is 213 KB in
size. Click on it to see the full size image. Notice the compression
artifacts. In particular, the distorted colours and pixels. You couldn't
really make out some lines because it's blurred. The second image is in
PNG format. It is only 68 KB in size, a 1/3 of the JPG. You can see that
it's perfectly clear and sharp. If you're interested in more
explanation, continue reading. But be forewarned that this could get
confusing. According to Wikipedia, .PNG images are generally smaller
than GIF but bigger than .JPG. However, PNG images produce sharper
quality than JPG if all else remain equal. Thus, for a clear technical
analysis chart image capture, PNG's file size is smaller than JPG (and
GIF) if the quality and resolution (height and width) are the same. That
is because PNG (and GIF) uses a lossless compression technique.
Meaning that the compressed image looks exactly the same as the
original. Whereas JPG uses a lossy compression technique. Meaning
the compressed image is merely close enough with the original. JPG would
lose out its advantage of smaller file size because it needs to increase
the quality (by reducing compression rate) to keep up with the quality
of PNG. And why the quality setting needs to be high for charts? Because
of the high contrast and non-uniform nature of stock charts. You can
rarely guess what a pixel is like from its neighbours. That is why
lossless image compression is highly preferred. Out of the commonly
supported trading platform export image formats out there, PNG is the
best there is. PNG is also widely supported by web browsers and
operating systems, so it's almost impossible that you will find a
computer that can't read it. In summary, here's a ranking in terms of
file size (for the same resolution and quality of image), #1 being the
best:
- PNG
- GIF
- JPG
Then a ranking for the quality at the same resolution and file size, #1
being the best:
- PNG
- GIF
- JPG
(Sorry, I couldn't do a table in this blog) Also note that PNG was
designed to be an improvement of GIF. So in most cases, PNG beats
GIF. Lastly, there's also BMP bitmap format. Some people may use it
because it's the default for Windows Paint and some other software.
Although, BMP is lossless too, it has no compression at all. For
example, the samples below were 213 KB and 68 KB for JPG and PNG,
respectively, but the BMP file is 3,319 KB for exactly the same image!
Using BMP is a waste of hard drive space for saving stock charts when
you can use PNG for the same image quality. [caption id=""
align="aligncenter" width="580" caption="JPG sample (213 KB)"][
]JPG sample (213 KB)[/caption] [caption id=""
align="aligncenter" width="580" caption="PNG sample (68 KB)"][
]PNG sample (68 KB)[/caption]