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A quick definition of stock photography might be helpful here. The wikipedia entry says that it consists of existing photographs that can be licensed for specific uses. Book publishers, specialty publishers, magazines, advertising agencies, filmmakers, web designers, graphic artists, interior decor firms, corporate creative groups, and others use stock photography to fulfill the needs of their creative assignments.

There are many big stock photography sites online. A quick search on google returns popular names like corbis, fotosearch, comstock. The businesses prosper by selling photos at different sizes, as the client specifies. The prices for these sizes vary to suit everyones needs: for small images the price is low, but these can mainly be used only on websites and other mediums that don’t require great resolution. The expensive large sizes are suited for printing, displays, posters etc.

We’ll talk more about this price - size dependence. Here’s a plot depicting this:

The blue line represents a plot of the price of an image found on stock photography sites (average price for the mentioned sites) versus the image size (in megabytes). The red line represents the best linear fit. This gives a trend for estimating larger size prices. The megapixels of the photo can be calculated by dividing the size in megabytes by 3.

A more detailed view of the data used

The resolution of the photos can be derived from their size (in MB) like this:

640 KB - approx. 640 x 480 pixels; 8.9″ x 6.7″ at 72 ppi
2 MB - approx. 1024 x 1280 pixels; 14.2″ x 17.8″ at 72 ppi
14 MB - approx. 1700 x 2550 pixels; 5.7″ x 8.5″ at 300 ppi
32 MB - approx. 2800 x 4200 pixels; 9.3″ x 14″ at 300 ppi
50 MB - approx 3400 x 5100 pixels; 11″ x 17″ at 300 dpi

Using the linear estimator from the figure we can calculate the price for a 150% and 200% times larger image. These factors are considered in the zoom column from the table below. The megabytes have a quadratic dependence on the zoom factor: Let’s take the 200% zoom (from 8 to 16, respectively from 60MB to 240MB). This means that the new size will be 200% the width * 200% the height of the photo. This gives a 4 times larger photo (60*4 = 240 MB).

I’ll describe several features related to the gallery display, image details page and the post option. These vary depending on whether you are logged in or not.

When logged out

Gallery

Contains pictures sorted and filtered by several criteria. You can choose from ordering the images by their rating (voted by users) or by their freshness (how recently added). Above every picture in the gallery there are several icons that allow voting and quick-view of any image. When moving the mouse over an image a zoomed portion is displayed. This allows you to get a quicker appreciation for the strongest details in the image. You can choose to see image from several categories (collections) that are displayed at the top of the page.

Details page

Clicking on an image in the gallery will show a page with more details. You can see the name, author and the author’s home page displayed below the picture. By clicking on the author you can see more images from the same artist. Also the collections that the picture is part of are shown on the left panel. You can vote for the image here too. Another important feature is the resize panel. Here you can select a resolution (your monitor size is chosen automatically but you can select another if you like), part of the image (crop), activate a sharpen level and resize the image.

Some of the features are enabled only for logged in users. Creating an account is free and fast. This is necessary because some restrictions have to be made regarding the processing time used when cropping, and also making possible equal rights when voting. Every user can only vote once (up, down or not do anything).

When logged in

Add & resize page

Here you can post your own images to reshade.com to use with the online image resizer. This will give you the option to enlarge and reshade your favorite pictures.

Gallery

Now you can click on the vote icons. The action will be attributed to the current user. The other things that change are the available options for your own posted pictures. By default images are posted public. This means that everybody can see them in the public gallery. You can make them private by clicking on the red-eye-with-a-cross icon above your images. To delete an image click on the red-cross icon.

You can now select to see your own images (my pictures from the top menu, these include the ones marked as private) or all images in the online image gallery.

Details page

Here you can crop pictures displayed on reshade.com including your own. The crop option is enabled only when logged in. Other options that become active are mainly available for you own posts. You can choose a name for your images and edit the collections they appear in (enter a custom name or choose from the default collections).

There are also other options that I didn’t mention like quick add. But the most important ones I did point out.

There are a few situations when resizing images on reshade.com won’t give the expected results. Here’s why:

Compression artifacts

First, very small images are also highly compressed (jpeg for example). The compression leaves artifacts in the image. They appear like out of place rectangles mostly around edges. These are mostly poorly visible in a small image. They can be taken as background noise or possibly even over-sharpening side-effects. When enlarged they become a lot more apparent. Reshading reduces their influence most of the time. But, there are of course plenty of very strongly compressed images out there. This implies lots of artifacts. If also using strong sharpening when reshading they become more apparent than usual.

Noise-like details

Small images are usually created from some larger versions of photos or other works. By shrinking an image more detail is gathered in a tighter space. This means that many noise-like effects will be created. Reshade tries to make sense of edges only above a threshold, considering the rest as noise. And noise is not a good thing, so reshading removes it. Because of this, enlarging very small images sometimes doesn’t work perfectly.

Sub-optimal sharper value

In most situations, a value of 100(%) for the sharper setting when resizing will be the best choice. Some images may require less of more depending on the situation. Try not to use too large a value. Sometimes this will create very unpleasant effects. If this happens reduce the sharper value or un-check the corresponding box (this will set sharpening to 0%)

Big blurry originals

Reshading will work only for up-sizing images. When down-sizing another method is used. This will not de-blur the image as it is currently implemented. If you would like reshade.com to use deblurring on the original please tell me.

Upsize limits

Reshade.com allows only resizes up to approximately a maximum of 1920×1200 pixels. But, because cropping is enabled the actual zoom factor spans from 0% to 300%. There is a limit to the number of crops/day (about 50).