Monthly Archives: March 2017

Image Histogram

An image histogram is a type of histogram that acts as a graphical representation of the tonal distribution in a digital image. It plots the number of pixels for each tonal value. By looking at the histogram for a specific image a viewer will be able to judge the entire tonal distribution at a glance. Image histograms are present on many modern digital cameras. Photographers can use them as an aid to show the distribution of tones captured, and whether image detail has been lost to blown-out highlights or blacked-out shadows. This is less useful when using a raw image format, as the dynamic range of the displayed image may only be an approximation to that in the raw file. The horizontal axis of the graph represents the tonal variations, while the vertical axis represents the number of pixels in that particular tone. The left side of the horizontal axis represents the black and dark areas, the middle represents medium grey and the right hand side represents light and pure white areas. The vertical axis represents the size of the area that is captured in each one of these zones. Thus, the histogram for a very dark image will have the majority of its data points on the left side and center of the graph. Conversely, the histogram for a very bright image with few dark areas and/or shadows will have most of its data points on the right side and center of the graph.

Image editors typically have provisions to create a histogram of the image being edited. The histogram plots the number of pixels in the image (vertical axis) with a particular brightness value (horizontal axis). Algorithms in the digital editor allow the user to visually adjust the brightness value of each pixel and to dynamically display the results as adjustments are made. Improvements in picture brightness and contrast can thus be obtained. In the field of computer vision, image histograms can be useful tools for thresholding. Because the information contained in the graph is a representation of pixel distribution as a function of tonal variation, image histograms can be analyzed for peaks and/or valleys. This threshold value can then be used for edge detection, image segmentation, and co-occurrence matrices.

Histogram vs LCD

Now that you know what a histogram is, you might be thinking to yourself that it would be easier to evaluate the exposure by looking at your LCD screen. This is a mistake! LCD screens have adjustable brightness that you can set yourself, so they’ll never give you a truly accurate rendition of your exposure. You’ll be able to tell if the shot is massively under or over exposed but the screen is really only useful for checking your composition. For accurate results, the histogram is your best friend!

Using The Histogram

The horizontal axis of your histogram goes from white through mid grey to black; from left to right. This is married to a vertical axis, which I always think looks a little like a mountain range, with various peaks and troughs. What this is actually representing is the relative quality of light for the given luminance of the scene. So, a perfectly balanced exposure will show a ‘hump’ in the middle, which tailors off on each side towards black or white. A digital camera that uses 8-bit sampling has 255 shades of grey, meaning that the histogram goes from 0 (black) to 255 (white). The arches on your histogram essentially show the brightness of an image. So, if you take a shot and see that the majority of your vertical arch is to the right of the image you will have a high-key image, which could be overexposed. Reverse this so that most of your data is on the left and you’ll have a low-key shot, which may be underexposed. Remember though that it’s not always a big fat negative to have a spike on one side of your histogram. For example, if you’re shooting with bright sunlight, it would be totally normal to see a sharp right-hand spike. A completely balanced histogram isn’t always going to be your goal. What you have to bear in mind is how to read the histogram, what’s in your scene in terms of brightness, darkness and contrast, and your desired result. With these elements taken into account, you can view your histogram and make adjustments – e.g. adjusting your exposure by changing your aperture, shutter speed or ISO or even recomposing your shot to change the amount of light or dark areas in your image.

Calibrate Photoshop

First things first, you’re going to want to make sure Photoshop is calibrated properly. This will allow you to view your photo at actual print size on the screen. To do this, you’ll want to find out what your screen resolution is, and then make the change in Photoshop’s settings.

Step 1: Measure the width of your screen

Measure your laptop or pc screen horizontally in inches. You can find this information in the owner’s manual, on the manufacturer’s website, or you could even just measure it yourself.

Step 2: Find your screen’s resolution

Next, make sure your monitor is in native resolution (if you have a retina display, make sure it’s set to the native resolution and not scaled up or down).

Step 3: Do the Math

Take the length of your screen horizontally in inches and divide it by the number of pixels horizontally.

Step 4: Change the Settings in Photoshop

Now, head over to Photoshop, and find your “Units & Rulers” section. This should either be under Photoshop > Preferences, or Edit > Preferences. Next to “Screen Resolution,” put in the PPI that you just calculated.Hit save!

Step 5: Check It Out

Now, open a photo in Photoshop, and view the print size to see what it will look like. To view the current print size go to View > Print Size. Make sure it’s in inches. This is what your image will look like when it’s printed. If you don’t see a ruler, enable it by going to View > Rulers and selecting it. The inches on the ruler that appear on the screen should represent an actual inch – you can verify this with an actual ruler to make sure. If everything lines up, congratulations! You’ll be able to view your images in actual print size now.

Change the Image Size

Ok! We’ve calibrated Photoshop. Now, let’s see how we can resize an image for print.

Here’s a look at how you can resize an image to a 6×4 print

You want to make sure the images that you’re printing will work for the frame that you have, or the photo album that you’ll be using.

Head to Image > Image Size. Make sure the box for “Resample” is unchecked. Find the Resolutionfield, highlight the number, and enter in 300. Once you’ve changed the resolution, the physical dimensions of the image, the width and height should change too. By unchecking the Resample box, and changing the resolution, you can make the image smaller, without losing any valuable data in the process.

Now, recheck the Resample box. Go to width, and enter in 6. The height box will probably read something like 3.979 – which is close enough for more cases when you’re printing, but in order to ensure absolute accuracy, you’ll want to take things a step further.

After hitting OK, navigate to the Marque Tool, located in the top left-hand corner, and select the rectangular marquee. Go up to the style drown-down dialogue and select Fixed Ratio. If your picture is in landscape orientation, you’ll want to input 3 for width and 2 for height at the top of the menu.

Now, go to the upper left-hand corner, click on the corner of the image, and drag open the box. You can drag the box around to position it. Once you’re happy with it, go to Image > Crop.Now go up to Image > Image Size, and, making sure the Resample box is checked, click the width to change it to 6. The height should automatically change to 4. Your picture should now be a perfect 6×4. Save your image to your desktop, and it’s ready to go for print!

Photographic Mosaic

In the field of photographic imaging, a photographic mosaic, also known under the term Photomosaic, a portmanteau of photo and mosaic, is a picture (usually a photograph) that has been divided into (usually equal sized) tiled sections, each of which is replaced with another photograph that matches the target photo. When viewed at low magnifications, the individual pixels appear as the primary image, while close examination reveals that the image is in fact made up of many hundreds or thousands of smaller images. Most of the time they are a computer-created type of montage. There are two kinds of mosaic, depending on how the matching is done. In the simpler kind, each part of the target image is averaged down to a single color. Each of the library images is also reduced to a single color. Each part of the target image is then replaced with one from the library where these colors are as similar as possible. In effect, the target image is reduced in resolution (by downsampling), and then each of the resulting pixels is replaced with an image whose average color matches that pixel.

In the more advanced kind of photographic mosaic, the target image is not downsampled, and the matching is done by comparing each pixel in the rectangle to the corresponding pixel from each library image. The rectangle in the target is then replaced with the library image that minimizes the total difference. This requires much more computation than the simple kind, but the results can be much better since the pixel-by-pixel matching can preserve the resolution of the target image. There is debate over whether Photomosaics are an art or mere technique. The making of a photomosaic is sometimes paralled and compared to forms of artistic appropriation, like literary assemblage. Artists such as David Hockney, Christopher Kates and Pep Ventosa have pioneered their own photographic mosaic techniques where multiple photographs are taken of a scene and then pieced together again to create a cohesive image.

Photographic mosaics are typically formed from a collection of still images. A more recent phenomenon, however, has been video mosaics which assemble video clips rather than still images to create a larger image. The closing credits of the 2005 PlayStation 2 game God of War, for example, incorporates a still image of the main character, Kratos, formed from a number of in-game videos. The term “video mosaic” also describes a large still image made from adjacent frames of video, such as those from video shots of geographic features like roads or cities. A mosaic of the video’s relevant frames replaces the full video, saving time and bandwidth, since the stills are much smaller.

Long Exposure Photography Tips

To help you start out, here are quick tips you should follow and keep in mind. These do not assure that you’ll become a master long exposure photographer, but they can help you do things right. These can help you make the proper start to your long exposure practice. Follow all these tips so you won’t wonder where you went wrong or why the shot didn’t come out the way you expected it to.

1. Avoid vibration of any kind

Make sure that your camera and tripod are on a steady, balanced surface. Some photographers even put something heavy on the tripod (like sand bags) to add some weight to it. The extra weight will make the tripod and camera sturdier. In addition to the extra weight, it will help if you use a remote shutter so there won’t be a need to press the shutter manually. Pressing the shutter can cause some vibration.

2. Be mindful of the weather

Days before the shoot, get all the information you can about the weather. Find ways to monitor the weather, especially if it has been raining for days or if it’s the rainy season. Do not schedule a shoot when the sky is cloudless or when the rains are pouring heavily. But pay attention to the weather forecast because conditions can change in a matter of minutes or hours. Do a location inspection several days before the shoot – study and familiarize it. This will give you ideas on how to set up the shoot and which shots to take. Likewise, an ocular inspection will give you the opportunity to study your concept, as well as to determine whether the location is perfect for what you want to achieve.

3. Visualize and compose your photo

Pay attention to the surroundings of your location and try to visualize how they can be incorporated into the shot or photo. This is important because you need to find a way to improve the scene or location for the long exposure shot. It is essential to pay attention to the total picture and not just the ones that are your focal interest.

4. Lock the focus and look for leaks

Make sure that your photo is well-composed. Do not lose your focus on the subject. You can manually lock the focus or use the shutter button if you are on autofocus mode. Be sure to lightly press (not full press) the button until the focus you want is achieved. Be mindful of the leaks. If there are leaks on the camera’s viewfinder (or anywhere else), you need to seal them off. To do this, you need to bring with you a black tape and any opaque material that you can use to cover the leaks. Even if the leaks are tiny ones, they can still affect the outcome of your long exposure shot.

5. Pay attention to the light

Whether you shoot in the daytime or at night, it is important to be mindful of the light. Is there ambient lighting? How much light can I get if I shoot at night? What man-made light sources can I use? Asking these questions will help you determine how much of your light requirement need to be improved and which ones should be utilized.