Archivi categoria: color

What’s a Red Pixel? Explaining Why These ‘Red’ Strawberries Aren’t Red

It’s all over Internet by now: the baffling picture of ‘red’ Strawberries, and the claim it does not contain any ‘red’ pixel.

There are a few versions going around the Internet, but for this post I downloaded the image that was originally posted by Akiyoshi Kitaoka‏ on twitter (with gamma: 1.0). Below you can see other images at different gamma levels. Clearly one can perceive the strawberries to be red in color; however, it is claimed that there are no ‘red’ pixels in the image. What does that statement mean?

A lot of people are claiming that this image has a lot of pixels with ‘R’ > 0 (meaning the red channel of the RGB image). Some others take a more strict definition of red and find many pixels with ‘R’ > 127. Still others are giving a counter argument that for pixels to be red, ‘R’ should be greater than both the ‘G’ and ‘B’ channel, i.e. ‘R’ > ‘G’ and ‘R’ > ‘B’.

Well I have a question for all these RGB thinkers: what color is the pixel with RGB values of [255, 254, 254]? It satisfies both ‘R’ > 127 and ‘R’ > ‘G’, ‘B’.

Its ‘white’… if you are still wondering.

So, how do we define ‘red’ pixels. One way is, instead of looking at the RGB values of pixels, to think in the language of ‘hue’, ‘saturation’, and ‘value’ or HSV. In the language of HSV, we need to find pixel with a ‘hue’ of ‘red’. Wikipedia gives a rather complicated definition of ‘hue’ as “the degree to which a stimulus can be described as similar to or different from stimuli that are described as red, green, blue, and yellow”.

Mathematically hue is defined as:

where hue (‘h’) then ranges from [0, 360] with both 0 and 360 implying ‘red’, 120 being ‘green’ and 240 being ‘blue.’

In simple language, hue captures the color of the pixel. Below you can see both the ‘R’ values and the ‘hue’ values (color coded to show the exact hue color) for the colorpicker image on the left (with hues mapped to 0-180 instead of 0-360). We can see that hue captures the colors accurately even if it is faded out, except when saturation is very low (look at the bottom of the image, which is almost white) where the hue estimates are a little off.

Now, given the understanding of hues, let’s see what hues are present in the strawberry image by Akiyoshi (gamma:1.0), again showing the true hue colors for each pixel (with hues mapped to 0-180 instead of 0-360).

Clearly, with the exception of a few pixels here or there all the pixels have a hue between ‘green’ and ‘blue.’ Those few pixels with red hue (hue < 20, or hue > 160 in the above image) are due to the poor estimation of hue when saturation/value is very low, mostly white like pixels in this particular case as highlighted in the figure below.

In other words, they are not influencing our perception in any significant way.

Finally, below we can see the same for all the four different gamma levels along with the ‘R’ value of all pixels. Although in some cases ‘R’ is close to 200, nevertheless the hue only ranges between 60 and 120, which is mostly green-blue range.

And finally, to really drive home the point, do you see any red tone in this image:

I bet not, unless you’re so determined to see a red pixel you’re imagining them. Well, this image consists of the same pixels as the strawberry image, just rearranged as per a magic function.

I hope this really drives the point home that its the positioning of the pixels that gives a ‘red’ perception—the pixels themselves are not ‘red’. In fact, I checked, and there are no pixels where ‘R’ is greater than both ‘G’ and ‘B’. I hope this clears any doubts that there are ‘red’ pixels in the images. There are no ‘red’ pixels. The image is indeed a masterpiece, making us perceive ‘red’ without any pixel being ‘red.’

About the author: Nikhil Rasiwasia is the Principal Research Scientist at Snapdeal. He has previously worked for Microsoft, UC San Diego, and Yahoo. This post was also published here.

How Color Filters Affect B&W Photos

If you’re new to film photography, chances are that you’ll get into shooting black and white sooner or later because you have been inspired by the masterpieces of old masters. But before you become the next Henri Cartier-Bresson or Sebastião Salgado, there are a few introductory things you should know.

Seeing the world in black and white is the main struggle for everyone at the beginning, but like with everything else, it can be learned and practiced with a simple understanding of how colors are translated into B&W. The human eye can distinguish approximately 500 shades of gray (well, some are limited to 50, but that’s another story). On the other hand, the scope of colors feels almost unlimited by comparison.

Why are some colors identical when turned into B&W?

Imagine a bus with only 50 seats (and no standing space) that has to carry 200 hundred people at the same time. If they all want to get in, some people will have to share the same seat. It’s the same with colors turned into B&W, there are too many to fit into the 500 shades of gray, so they must be compressed to all fit in the bus. To put this into an image, I’ve turned the 6 basic colors into gray so you can see how they translated in B&W.​

We can see that some share the same seat. Look at the yellow and orange: they are nearly identical, so that affects sunset pictures. Another interesting comparison is the red and green: they are almost identical, which makes pictures of poppy field look like a muddy gray landscape… how disappointing!

Picture by Friederike Hiepko

Does that mean that I can’t take a good B&W picture of a poppy field?

Hopefully not! There are ways to change the way B&W film responds to colors. For this, you will have to rely on colored filters. Let me briefly introduce each of them:

Yellow filter: The classic among black and white photographers. Blue skies are darkened, which helps to increase the separation with the clouds. Other colors like green, red, orange and yellow will appear brighter.

Orange filter: It comes right after the yellow in terms of strength. Blues will become even darker for a more dramatic effect. Most warm colors will also show brighter than greens.

Red filter: This one is the strongest. Red will turn into white and foliage appear very dark. If you want your poppy flowers to pop out that’s the one but pay attention to the background. We can see at the horizon the light green turned also into white. It works best with darker shades of green like in the foreground.

Green filter: The opposite of the previous one. Red will turn darker and green brighter. It’s not very popular because of its limited span of action, but it can give very interesting effect when used on the correct scene.

Blue filter: Another uncommon filter but if you want to brighten blues it’s the one! Warm colors will be darkened and red turned into black, which can help to separate elements in a mixed colored scene. It also increases fog and haze which can help to emphasize a moody landscape.

One important thing about using filters is that they all reduce the amount of light by 1 or more stop. So you must compensate this loss of light when exposing. It varies depending on the filter so refer to the manufacturer’s product information.

Considering contrast when shooting B&W

Now that we know how to manipulate each color, the other element to consider when shooting B&W film is contrast.

Depending on which style you are going for, contrast will play a major role. There are no colors to define the mood of your image so the type of light is probably the most important element to create the ambiance you want to achieve. Direct sunlight can be a nightmare for color photographers, but not in B&W. If you want to shoot street photography, for example, it’s exactly what you are looking for as it will create contrast and harsh edges in your image. It will help to detach the subject from its environment and re-enforce your composition.

If you prefer a softer ambiance, look for an atmosphere with low contrast. Cloudy or foggy days are perfect for this type of images. The light is evenly distributed which result in a mellower ambiance. It’s also the ideal situation for shooting female portraits, as it makes skin looks softer and more pleasing.

Another crucial element that affects contrast is the type of film you shoot with. B&W films don’t react the same way and it’s important that you choose the proper one based on what you are looking for. This is really a matter of personal tastes and there is no right or wrong film here, just the one you like.

If I want to go for a contrasty image, Ilford HP5 or Kodak Tri-X are my go to films. If I’m aiming for a softer image, Fomapan 200 or 400 is the one I prefer.

“There are so many films, which one is the best?”

Choosing film can be overwhelming when beginning so if you are not sure about which one you should use, check out the “Film Dating” quiz I created. It helps to find the right film for you in just a few clicks.

The last point that will influence the result of your image is the development technique or chemicals you will use. There are many ways to go when developing and the combinations of film/developer can completely change the look of a negative.

I’ll take the example of stand development, as that’s the one I’m more familiar with. Depending on the film and developer you are using, it can completely change the contrast of your photo. I have tried this approach with Fomapan 400 (low contrast) and Kodak Tri-X (high contrast).

When developed using the stand technique using Ilfotec DD-X developer, Fomapan 400 turned into a super contrasty film. On the opposite, Kodak Tri-X, which is known for being contrasty, turned into a flatter image with this process. These are just examples and combinations are infinite when developing. The best is to experience yourself with the chemicals and films you have at home. If you want more information about developing time for each film and chemical, check out this Massive Dev Chart.

We’ve now seen that many factors can influence a B&W image, but the most important point is your ability to see the world in monochrome. That’s what requires the most practice but with experience, you’ll become better — it’s just a matter of training your imagination.

If you are just starting out, forget about everything else and just concentrate on imagining a scene in B&W. Once you’ve gained more experience, it’ll be easier to apply what you’ve read above.

About the author: Vincent Moschetti is an Ireland-based photographer who is in the middle of a year-long experiment where he’s shooting only film photography. You can find more of his work or follow along on this adventure by visiting his website or following him on Facebook and Instagram. This post was also published here.

This Simple Video is the Perfect CMYK Demo: See Subtractive Color in Action

CMYK—which stands for Cyan, Magenta, Yellow, and Key (or Black)—is the color model used in most printing. It’s called a subtractive color model, and if you don’t understand what that means or how it works, this brilliant little demo should help.

The video was posted by the Instagram account @physicsfun, and it shows how each subsequent color after the Key below subtracts brightness from the background to create a final color image. In CMYK, all the colors together overlap to create black, compared to the additive RGB model where white is the result of combining Red, Green, and Blue.

All @physicsfun had to do was stack four CMYK coasters on on top of the other, and Vermeer’s painting “Girl with a Pearl Earring” emerges. Check out the video below:

A video posted by physicsfun (@physicsfun) on

(via Retouchist)

Macro Photos of Backlit Autumn Leaves Explode with Color and Texture


In the Autumn of 2015, I decided to try and capture the beauty of autumn leaves in a different way. My idea was to highlight the leaves from beneath to emphasize the lines and the color of decaying parts.

For more accurate sharpness, I taped the leaves onto a white sheet of paper to make them more flat, and set them on a glass tabletop.



I used 2 speedlites for this process, one under the glass and the other at twelve o’clock, half a meter from the leaf. To my surprise, the results were amazing! The colours just exploded with contrast, providing chaotic textures.

Unfortunately, I was lacking a good tripod so I had to shoot the images hand-held, and all I had to do is snap the image with the texture in focus and the light will do the rest, which is how I ended up with 18 macro texture images.



















As for gear that I used, it’s actually really simple and cheap. My camera was a Canon 550D (T2i), the lens an old Russian Zenit Helios 58mm f/2 44M-6 reversed using a Reverse m42 adapter and extension tubes, and the lights 2 yongnuo YN460II flashes.

All of the photos were taken at f/8 and 1/200 of a second hand-held, then edited in Lightroom and Photoshop.


I hope to inspire others and prove that you can do almost anything you imagine, even with low-cost equipment. Autumn of 2016 has just begun, good luck!

About the author: Neven Krcmarek is a Croatia-based photographer and editor. You can find his product, portrait, and landscape photography on his website or by following him on Unsplash where all of these Autumn leaf photos are available to download for free.