How To Convert Images Using Linux

How To Convert Images Using Linux


This guide will show you how to manipulate images using the Linux command line.

You will find out how to resize an image both in terms of file size and in scale. You will also learn how to convert between multiple file types such as from JPG to PNG or GIF to TIF.

The Convert Command

The convert command is used to convert an image. The format is as follows:

convert [input options] input file [output options] output file.

How To Resize An Image

If you are going to include an image on a webpage and you want it to be a particular size then you could use some CSS to resize the image.

It is actually better though to upload the image as the correct size in the first place and insert it into the page.

This is of course just one example why you might want to resize an image.

To resize an image use the following command

convert imagename.jpg -resize dimensions newimagename.jpg

For example to convert an image to be 800×600 you would use the following command:

convert imagename.jpg -resize 800x600 newimagename.jpg

If by converting to the specified dimensions theaspect ratio will be messed up the image will be resize to the closest ratio.

To force the conversion to be the exact size use the following command:

convert imagename.jpg -resize 800x600! newimagename.jpg

You don’t have to specify the height and the width as part of the resize command. For example if you want the width to be 800 and you don’t care about the height use the following command:

convert imagename.jpg -resize 800 newimagename.jpg

To resize an image to be a specified height use the following command:

convert imagename,jpg -resize x600 newimagename.jpg

How To Convert From One Image Format To Another

If you have a JPG file and you wish to convert it to a PNG then you would use the following command:

convert image.jpg image.png

You can combine many different file formats. For example

convert image.png image.gif

convert image.jpg image.bmp

convert image.gif image.tif

How To Adjust The File Size For An Image

There are a number of ways to change the physical file size of an image.

  1. Change the aspect ratio (make it smaller)
  2. Change the file format
  3. Change the compression quality

Reducing the size of the image will make the file size smaller. In addition using a file format that includes compression such as JPG will enable you to reduce the physical file size.

Finally adjusting the quality will make the physical file size smaller.

The previous 2 sections showed you how to adjust the size and file type. To compress the imagetry the following command:

convert imagename.jpg -quality 90 newimage.jpg

The quality is specified as a percentage. The lower the percentage the smaller the output file but obviously the final output quality is not as good.

How To Rotate Images

If you have taken a photo in portrait but you want it to be a landscape image you can rotate the image using the following command:

convert imagename.jpg -rotate 90 newimage.jpg

You can specify any angle for rotation.

For example try this out

convert imagename.jpg -rotate 45 newimage.jpg

Convert Command Line Options

There are dozens of command line options that can be used with the convert command as shown here:

Options are processed in command line order. Any option you specify on the command line remains in effect for the set of images that follows, until the set is terminated by the appearance of any option or -noop. Some options only affect the decoding of images and others only the encoding. The latter can appear after the final group of input images.

For a more detailed description of each option, see Imagemagick.


join images into a single multi-image file


drawing transform matrix


remove pixel aliasing


append a set of images


average a set of images


the background color

-blur x

blur the image with a gaussian operator

-border x

surround the image with a border of color


the border color


set the color of the annotation bounding box


megabytes of memory available to the pixel cache


the type of channel


simulate a charcoal drawing

-chop x{+-}{+-}{%}

remove pixels from the interior of an image


apply the clipping path, if one is present


merge a sequence of images


colorize the image with the pen color


preferred number of colors in the image


the type of colorspace


annotate an image with a comment


the type of image composition


the type of image compression


enhance or reduce the image contrast

-crop x{+-}{+-}{%}

preferred size and location of the cropped image


displace image colormap by amount


enable debug printout


break down an image sequence into constituent parts


display the next image after pausing

-density x

vertical and horizontal resolution in pixels of the image


depth of the image


reduce the speckles within an image


specifies the X server to contact


GIF disposal method


apply Floyd/Steinberg error diffusion to the image


annotate an image with one or more graphic primitives


detect edges within an image


emboss an image


specify the font encoding


specify endianness (MSB or LSB) of output image


apply a digital filter to enhance a noisy image


perform histogram equalization to the image


color to use when filling a graphic primitive


use this type of filter when resizing an image


flatten a sequence of images


create a “mirror image”


create a “mirror image”


use this font when annotating the image with text

-frame x++

surround the image with an ornamental border

-fuzz {%}

colors within this distance are considered equal


level of gamma correction

-gaussian x

blur the image with a gaussian operator

-geometry x{+-}{+-}{%}{@} {!}{}

preferred size and location of the Image window.


direction primitive gravitates to when annotating the image.


print usage instructions


implode image pixels about the center


use this type of rendering intent when managing the image color


the type of interlacing scheme


assign a label to an image


adjust the level of image contrast


the type of list


add Netscape loop extension to your GIF animation


choose a particular set of colors from this image


Specify a clipping mask


store matte channel if the image has one


apply a median filter to the image


vary the brightness, saturation, and hue of an image


transform the image to black and white


morphs an image sequence


create a mosaic from an image sequence


replace every pixel with its complementary color


add or reduce noise in an image


NOOP (no option)


transform image to span the full range of color values


change this color to the pen color within the image

-page x{+-}{+-}{%}{!}{}

size and location of an image canvas


simulate an oil painting


specify the pen color for drawing operations


efficiently determine image characteristics


pointsize of the Postscript, OPTION1, or TrueType font


image preview type


process a sequence of images


add ICM, IPTC, or generic profile to image


JPEG/MIFF/PNG compression level

-raise x

lighten or darken image edges

-region x{+-}{+-}

apply options to a portion of the image

-resize x{%}{@}{!}{}

resize an image

-roll {+-}{+-}

roll an image vertically or horizontally

-rotate {}

apply Paeth image rotation to the image


scale image with pixel sampling

-sampling_factor x

sampling factors used by JPEG or MPEG-2 encoder and YUV decoder/encoder.


scale the image.


set scene number


pseudo-random number generator seed value

-segment x

segment an image

-shade x

shade the image using a distant light source

-sharpen x

sharpen the image

-shave x

shave pixels from the image edges

-shear x

shear the image along the X or Y axis

-size x{+offset}

width and height of the image


negate all pixels above the threshold level


displace image pixels by a random amount


color to use when stroking a graphic primitive


set the stroke width


swirl image pixels about the center


name of texture to tile onto the image background


threshold the image


tile image when filling a graphic primitive


transform the image


make this color transparent within the image


tree depth for the color reduction algorithm


trim an image


the image type


the type of image resolution

-unsharp x

sharpen the image with an unsharp mask operator


use the pixmap


print detailed information about the image


FlashPix viewing parameters

-wave x

alter an image along a sine wave


write an image sequence [convert, composite]


For more information read the manual page for the convert command:

man convert



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